Advanced Engineering Tech - What makes more torque................

I saw this section and had a question.

What makes more torque....ci's or longer strokes.

Like if you had two 454 cubic inch engines, everything equal except different stroke and bore: Both N/A engines.

1) 4.250 stroke x 4.125 bore = 454

2) 4.125 stroke x 4.185 bore = 454

Will engine #1 have more torque???????

choice 1.....stroke wins over bore, for low end power.

I saw this section and had a question.

What makes more torque....ci's or longer strokes.

Like if you had two 454 cubic inch engines, everything equal except different stroke and bore: Both N/A engines.

1) 4.250 stroke x 4.125 bore = 454

2) 4.125 stroke x 4.185 bore = 454

Will engine #1 have more torque???????

Where in the rpm range you will make those numbers is what will be different. Engine #1 will make the power lower in the rpm range than engine #2 because of the larger stroke. Engine #2 will require more rpm to produce the same numbers as engine #1.

"There is no replacement for displacement" The bigger the better.

There is way more to this which has been argued for a long time . A longer stroke does have more leverage , but a larger bore has a greater surface area for the pressure to act upon plus you can put more cylinder head on it . Do a search and you'll find tons of info ranging from simpleton to in depth science . I'd pick the larger bore and turn some rpms .

http://ls1tech.com/forums/showthread.php?t=1006863

in simple terms...

a naturally aspirated engine can achieve 12-13 bar bmep (without going to extreme lengths)

BMEP effectively Torque/displacement.. which means bore and stroke are used to optimize cylinder filling, friction/piston side load forces, combustion, mixture motion, rpm capability, etc.. but at the end of the day.. displacement is the only way to make torque NA, but Power can be made through RPM or Torque

Where in the rpm range you will make those numbers is what will be different. Engine #1 will make the power lower in the rpm range than engine #2 because of the larger stroke. Engine #2 will require more rpm to produce the same numbers as engine #1.

"There is no replacement for displacement" The bigger the better.

Ok, so the answer is the engine with the longer stroke will make more torque, both being 454ci, right?

Reason I ask is: I know a guy with 422ci, its got a 4.125 stroke x 4.030 bore. Another guy has a 428ci, but he has 4.0 stroke x 4.125 bore.

The 422 makes considerably more torque everywhere.
Both are LS6 headed and LS6 intake. Same compression.

NO!

that is incorrect, please re-read my statement above.

NO!

that is incorrect, please re-read my statement above.

I read it, but I guess I'm missing something.

Because the 422 makes alot more torque than the 428....only difference in the two engines (which BTW, were both built by the same man) is the stroke. Both built as N/A engines for the street. So, unless I'm not getting something, that longer stroke seems like its the reason for more torque.

Also, the 422 makes more power, 535 RWHP M6. Not sure of the rpm.

One other thing: 422 is iron block and the 428 is aluminum. Don't think that can make a difference though.


.

Ok, so the answer is the engine with the longer stroke will make more torque, both being 454ci, right?

Reason I ask is: I know a guy with 422ci, its got a 4.125 stroke x 4.030 bore. Another guy has a 428ci, but he has 4.0 stroke x 4.125 bore.

The 422 makes considerably more torque everywhere.
Both are LS6 headed and LS6 intake. Same compression.

Same cam?? Same exact heads?? On relatively equal displacement engines like you have listed here, the topend is the variable. Unless they are exactly the same, it is a moot point.

Same cam?? Same exact heads?? On relatively equal displacement engines like you have listed here, the topend is the variable. Unless they are exactly the same, it is a moot point.

Yes. The same shop built both engines, the same guy. They have the same exact parts. LS6 ported heads and LS6 intakes were done by the shop that built both engines, stock ported TB's. Same exact cr. Both cams are in the 230's. M6's. 428 has no A/C and aluminum block. Only difference is the longer stroke for the 422ci.

Oh well, I guess it has to be the stroke. Some questions just can't be answered.

:chug:

Stroke does not = torque.

Cubic inches is where it's at. :)

I think this has been said, but here it goes again.
The longer stroke will make torque sooner in RPM. This is due to two things, increased leverage, and piston speed. If you have a longer arm spinning at X RPM, it will have to be moving the piston faster than the shorter stroke.
So, yes, the PEAK torque number should be higher on the longer stroke because of the two matters spoke about earlier.
Now, the other argument comes up with the larger surface area on the piston. This is correct. I have made a spreadsheet that shows increasing piston size will do a greater amount of work due to increased area. This however does not take piston speed in to account.

Hope this helps. If it were me, I would build the big bore combo because the CR will be a bit higher and the cylinder head will flow better making greater horsepower potential.

I think this has been said, but here it goes again.
The longer stroke will make torque sooner in RPM. This is due to two things, increased leverage, and piston speed. If you have a longer arm spinning at X RPM, it will have to be moving the piston faster than the shorter stroke.
So, yes, the PEAK torque number should be higher on the longer stroke because of the two matters spoke about earlier.
Now, the other argument comes up with the larger surface area on the piston. This is correct. I have made a spreadsheet that shows increasing piston size will do a greater amount of work due to increased area. This however does not take piston speed in to account.

Hope this helps. If it were me, I would build the big bore combo because the CR will be a bit higher and the cylinder head will flow better making greater horsepower potential.


Thanks. Sometimes it just takes another way to explain it.

Schwanke has it right! The most accurate description describing torque increase due to either increasing stroke or increasing bore I've read (besides my own posting about two weeks ago on the same topic :D). On deciding which way to go, decide what you want your usable rpm range to be. If you want a high winder, go with the large bore/short stroke combo. If you want a low puller, go with the smaller bore/long stroke combo.

Ok, so the answer is the engine with the longer stroke will make more torque, both being 454ci, right?



There is obviously more than 1 variable that will change the output numbers of an engine. Increased stroke in any engine brings the max torque number down in the curve so you have more low RPM grunt. In a perfect situation the only difference should be WHERE the max torque is produced, not how much.

If the heads, cam, compression, ring tension, etc are all the same on both engines, the engine with the longer stroke will end up making more power because you have the same amount of pressure from the air/fuel being burned pushing down on the piston. The difference, however is the increased leverage of the longer stroke is multiplying that force from the power stroke more than the shorter stroke.

One thing I didn't see mentioned is that if both heads are the same, then the big bore motor is handicapped with heads that are not big enough to take advantage of the increased surface area, thus hurting cylinder filling. The smaller bore motor is taking full advantage of the heads because the heads are sized for the bore size, and maximum cylinder filling is taking place. If you used the same heads but with wider combustion chambers to fit the bigger bore, torque and hp figures would be closer with the 2 engines. However, with the slower piston speed of the bigger bore motor, you'll still have to spin it higher than the long stroke engine to achieve the same numbers.

For the bigger bore motor to achieve the same numbers with the same power band as the longer stroke motor, you'll need heads with smaller ports but with the same flow to achieve the higher velocity needed to fill the cylinders at the same rate but with lower piston speeds. Only then will the big bore motor equal the long stroke motor in midrange torque.

Jason

If the heads, cam, compression, ring tension, etc are all the same on both engines, the engine with the longer stroke will end up making more power because you have the same amount of pressure from the air/fuel being burned pushing down on the piston. The difference, however is the increased leverage of the longer stroke is multiplying that force from the power stroke more than the shorter stroke.

One thing I didn't see mentioned is that if both heads are the same, then the big bore motor is handicapped with heads that are not big enough to take advantage of the increased surface area, thus hurting cylinder filling. The smaller bore motor is taking full advantage of the heads because the heads are sized for the bore size, and maximum cylinder filling is taking place. If you used the same heads but with wider combustion chambers to fit the bigger bore, torque and hp figures would be closer with the 2 engines. However, with the slower piston speed of the bigger bore motor, you'll still have to spin it higher than the long stroke engine to achieve the same numbers.

For the bigger bore motor to achieve the same numbers with the same power band as the longer stroke motor, you'll need heads with smaller ports but with the same flow to achieve the higher velocity needed to fill the cylinders at the same rate but with lower piston speeds. Only then will the big bore motor equal the long stroke motor in midrange torque.

Jason

I just couldn't let this post go.

Truly unbelievable! I've never seen all of these erroneous ideas in one post before. It boggles the mind!

I don't mean to single you out, Jason, because others have said much of the same bovine scat but never all in one post. Your post is a "target rich enviornment." Tell me you were just picking out various buzz words and other folks ideas and stringing them together. Please don't believe what you posted.

I suggest you stick to your day job selling rather than advise on engine design. If you want to delete your post, I'll delete my quote of it. You probably won't because you don't believe what I'm saying. More's the pity.

Jon

I guess people get this info from magazines?!

The leverage statement really cracks me up! :lol:

I guess people get this info from magazines?!

The leverage statement really cracks me up! :lol:

Umm, that is how torque is multiplied. If you put a 50lb force on a 1 foot arm, you have 50 foot pounds of torque. If you have the same force with a 2 ft arm, you have 100 foot pounds of torque. So that statement is accurate.

Sorry to pop your bubble.

Mr. Sanderson and V8pwr are correct, you get more torque from the added leverage.

To increase stroke, you move the rod journal out farther from the centerline of the crank. In doing so, you increase the amount of torque placed on the crank. (Think: what exerts more force? 50lbs on a 1-foot breaker bar or 50lbs on a 5-foot breaker bar.)

But, it isn't the only reason you get such a nice increase in torque.

With the longer stroke, you also get a longer distance in which the combustion gasses are exerting force on the power stroke. This means each cylinder has more time to exert force on the crank during each power stroke.

Combine these two effects and enjoy a very nice torque monster.

It should be noted:

With a longer stroke you add more torque, but you also exert more force on the rod bolts on the upstroke due to the increased speed at which the piston is travelling at any given rpm. This limits your max rpm a little more unless you upgrade rod bolts.

Umm, that is how torque is multiplied. If you put a 50lb force on a 1 foot arm, you have 50 foot pounds of torque. If you have the same force with a 2 ft arm, you have 100 foot pounds of torque. So that statement is accurate.

Sorry to pop your bubble.


Yep, if you are tightening a bolt, you are correct.

However to relate this to engines, with a given displacement a longer stroke engine will necessarily have a smaller bore and less area for the expanding combustion gasses to push on. That means less force pushing on the longer lever arm. It equals out. *

OK, I'm assuming both engines get the same combustion pressure because they breathe in the same amount of air. Usually the larger bore engine breathes better with the same heads, but let's say they are the same. We also don't need to go into more friction from a longer stroke, but I'm not telling you anything you don't already know as a professional engine buiilder.

I just don't like to see less knowledgeable folks misled.

*Do the math for a 4.000 bore x 4.000 stroke 402 then figure the bore for 4.250 stroke 402, and then compare areas of the pistons and the stroke ratio. Or you could just take my word for it. :)

Theres no school like old school!
Right stroker?

HOW ABOUT THIS ONE, STROKER!
Biggest stroke the block will take.
Biggest bore the block will take w/out compramising wall strength.
Maximum compression of desired fuel{street most likley}
1.63-1to 1.7-1 r/s ratio
w/good heads w/highvelocity/hi-volume ports
the right cam for the combo!

Theres no school like old school!
Right stroker?

Old School and Old Fool...I resemble both of those.

Umm, that is how torque is multiplied. If you put a 50lb force on a 1 foot arm, you have 50 foot pounds of torque. If you have the same force with a 2 ft arm, you have 100 foot pounds of torque. So that statement is accurate.

Sorry to pop your bubble.


The only bubble needing popped is yours. :) Old SStroker said it best.

Mr. Sanderson and V8pwr are correct, you get more torque from the added leverage.

To increase stroke, you move the rod journal out farther from the centerline of the crank. In doing so, you increase the amount of torque placed on the crank. (Think: what exerts more force? 50lbs on a 1-foot breaker bar or 50lbs on a 5-foot breaker bar.)

But, it isn't the only reason you get such a nice increase in torque.

With the longer stroke, you also get a longer distance in which the combustion gasses are exerting force on the power stroke. This means each cylinder has more time to exert force on the crank during each power stroke.

Combine these two effects and enjoy a very nice torque monster.


totally wrong... while the statement about 50lbf on a 2 foot lever arm making more torque than 50lbf on a 1 foot lever arm is CORRECT, you completely missed the fact that you dont have a constant force because for a given displacement, your bore is changing as well (i.e. decreasing the force in a porportional rate to the increase in lever arm)

What makes torque? Increasing the amount of chemical energy that can be released and utilized efficiently during a combustion event. So..

A. you can work on adding more air and fuel per event
B. you can work on increasing the efficiency of the event

WOW , this keeps going and going . An example some of you might respect is the C5R program which was a 427 and a rev limit under 7k if I remember . They choose a larger bore shorter stroke combo than the usual 4.125x4.0 for some odd reason , and obviously it worked .

WOW , this keeps going and going . An example some of you might respect is the C5R program which was a 427 and a rev limit under 7k if I remember . They choose a larger bore shorter stroke combo than the usual 4.125x4.0 for some odd reason , and obviously it worked .

larger bore allows larger valves..

but yes, there are tradeoffs going extreme in either direction

good engine design usually takes full advantage of the regulations... thats why limited displacement class engines usually have large bore and spin fast.

Displacement = torque (in a very general sense)
Power = torque x rpm

selection of bore, stroke, valvetrian design, materials, etc.. are all to optimize the engine for its operating environment..

pretty simple really.. but it seems we have an unlimited supply of people who only made it through the first week of statics class.. and only know force x distance = torque... and assume large stroke means more torque.

O.K. - the math tells all people.

Engine Torque = (hm ) (hc ) (ht) (hv) (ra) (Vd) (N/2) (F/A) (Qhv) (1 / 4pi)


Where hm = Engine mechanical efficiency (power in / power out)

hc = Engine combustion efficiency

ht = Engine thermal efficiency

hv = Engine volumetric efficiency

ra = Air density

Vd = Engine displacement volume

N = Engine speed in radians per second

F/A = Mass of fuel divided by mass of air

Qhv = Heating value of engine fuel

pi = 3.14

If you are comparing engines with the same efficiencies, F/A ratios, fuel, and air density, then there are only two variables left: RPM and Displacement.

Raise and lower RPM and/or displaced volume in the equation and you can see the impact on torque. Stroke is a direct impact on displaced volume, so the advantages are clear.

I believe that stroker engines may also have an impact on the hv (volumetric efficiency) term in the above equation. Stroker engines often have longer piston dwell times at the top and bottom of the cylinder, which allows more time for air and fuel to enter/exit the cylinder. This provides a better A/F charge and contributes to the power gains.

.. but it seems we have an unlimited supply of people who only made it through the first week of statics class.. and only know force x distance = torque... and assume large stroke means more torque.


That made me ROFL, DanO. Thanks!

Unfortunately, the "one-weekers" are preaching to those who never had the opportunity to take those kind of classes. I'm not trying to be a snob about having a physics or engineering background, but it surely helps one understand how the world works.

I hate to see bad info passed on as gospel. That just keeps dumbing down the understanding level of many car enthusiasts. The torque wrench idea is easy for most folks to grasp, while the force resulting from combustion pressure/piston area is not as intuitive. It can be taught however. IMO, that's what "Advanced Engineering Tech" forums should be about.

Jon

Wow, still chatting about this topic.

All I know is a 422 and a 428 built by the same guy, using the identical top end, the cams were almost exactly the same and they both have the same compression 11:1 and are M6's in F-Bodies.

Only difference is the 422 has a longer stroke and is an iron block. (we know iron/aluminum have no bearing on power output). It makes more power and torque everywhere. Don't have both dyno sheets, but I do know that the 422makes 535 RWHP and the 428 makes 515 RWHP, both at 6,400 rpm, same chassis dyno. The torque was more on the 422 everywhere.

Increased Cubic Inches obviously will keep making more power than the smaller engine, doesn't take a class to tell a person that. But its pretty clear that a longer stroke, all else being equal, and in this case all else is pretty much identical right down to the man who built them both using the same exact brand parts......makes more Torque, period. Even more than an engine with a little more cubes than another, if again, all else is held close to equal.

So the argument is over I guess, I can tell these few guys that were arguing about it, stroke is what causes more torque to be made, compared to a shorted stroke being used in a given cube engine.

:chug:

i always heard that stroke makes the torque while the advantages of a small stroke but big bore is for high rpms and hp, thats why small engine cars like Ferraris DONT have big long strokes, because with a long stroke it would have to move too deep, but if you have a small stroke you can even it out with a really big bore, so that now you dont move so deep so you can go much faster, hence low torque but higher peak hp due to being able to rev much faster.

Ok i tottally over complicated it the way i explained it but hopefully you get my point. Im so done talkin about deep long strokes lol.

i always heard that stroke makes the torque while the advantages of a small stroke but big bore is for high rpms and hp, thats why small engine cars like Ferraris DONT have big long strokes, because with a long stroke it would have to move too deep, but if you have a small stroke you can even it out with a really big bore, so that now you dont move so deep so you can go much faster, hence low torque but higher peak hp due to being able to rev much faster.

Ok i tottally over complicated it the way i explained it but hopefully you get my point. Im so done talkin about deep long strokes lol.

Yeah, F1 and CART type engines that have tiny strokes and spin to the moon make huge HP, but not much TQ, comparitively.

ugh.. yet again..


"i know this guy who built two engines"

"there is this engine builder who"


please, i dont mean to be a jerk but this is an advanced engineering forum.

Wow, still chatting about this topic.

All I know is a 422 and a 428 built by the same guy, using the identical top end, the cams were almost exactly the same and they both have the same compression 11:1 and are M6's in F-Bodies.

Only difference is the 422 has a longer stroke and is an iron block. (we know iron/aluminum have no bearing on power output). It makes more power and torque everywhere. Don't have both dyno sheets, but I do know that the (smaller) 422makes 535 RWHP and the (larger) 428 makes 515 RWHP, both at 6,400 rpm, same chassis dyno. The torque was more on the 422 everywhere.

Increased Cubic Inches obviously will keep making more power than the smaller engine, doesn't take a class to tell a person that. But its pretty clear that a longer stroke, all else being equal, and in this case all else is pretty much identical right down to the man who built them both using the same exact brand parts......makes more Torque, period. Even more than an engine with a little more cubes than another, if again, all else is held close to equal.

So the argument is over I guess, I can tell these few guys that were arguing about it, stroke is what causes more torque to be made, compared to a shorted stroke being used in a given cube engine.

:chug:

How can one dispute such well documented facts especially when run in two different cars? You asked the original question, but you really already had your mind made up. Too bad.

The chugging smilie seems apt for you. You do that a lot? Reread your own post.

One probably had a 10 bolt and the other a 12 bolt. :)

How can one dispute such well documented facts especially when run in two different cars? You asked the original question, but you really already had your mind made up. Too bad.

The chugging smilie seems apt for you. You do that a lot? Reread your own post.

Its the closest thing I see for this comparison.

Unless someone wants to build two identical engines, one with a longer stroke, and put them in one car and do tests for us. Doubt anyone will waste their money and time.

Everything is identical except the stroke in these two engines, as already I said. When one makes considerably more torque.....what would you say is the reason????

Do you think the 428 car has cement in the drive shaft or something and its a trick.

Its plain to see why the 422 makes more torque. Whats the big deal. I asked here to settle an agrument between some people. Everyone is wondering why the 422 has the 428 beat pretty good.

STROKE!!!!!

ugh.. yet again..


"i know this guy who built two engines"

"there is this engine builder who"


please, i dont mean to be a jerk but this is an advanced engineering forum.


Only by its title, DanO. Too many zero-weekers with closed minds...a deadly combination if ever there was one. ;)

Only by its title, DanO. Too many zero-weekers with closed minds...a deadly combination if ever there was one. ;)


Old SStroker,

You guys are fighting a losing battle. I post very little in here just because of the overwhelming amount of MIS-information being spread. Unfortunately, with the state of the educational system in this country being what it is and the total lack of a fundimental understanding any of the hard sciences, even your explainations which make total sense to me and for the most part match up perfectly with many years of real world hands on experience I have, are falling on deaf ears...

Too bad.

Thanks for trying. :cheers:

Shane

I just couldn't let this post go.

I don't mean to single you out, Jason, because others have said much of the same bovine scat but never all in one post. Your post is a "target rich enviornment." Tell me you were just picking out various buzz words and other folks ideas and stringing them together. Please don't believe what you posted.


Stroker,

I'm all ears if you care to explain in a few sentences where I'm wrong. I will say that when I finished the post, I was pretty unsatisfied with how clearly I worded everything, but I decided to click "Post" thinking it was adequate. obviously not... :lol:


In a nutshell, what motivated me to make the post is I have seen a number of big bore/short stroke motors with carefully matched combos put out very flat torque curves right in line with a regular stroker motor. All had heads that flow well with the smallest ports possible (AFR seems to be the best at this for out-of-box heads), about as much compression possible on 93 octane, generally a tight valve overlap to not bleed off as much compression as a wider overlap, and intakes ported to flow-match the heads. There's more to it, but these are the obvious factors.

I do understand the concept of leverage with longer strokes, but I think my point can be at least somewhat supported when you compare a Ford 5.4 2V and a 350 Vortec, both truck engines. One is a long stroke/small bore, and the other a big bore/small stroke, but they both have identical torque curves with the Chevy even having a slight advantage.

I'm leaving out alot of things and probably missed some, but do you get where I'm coming from?

Jason

Stroker,

I'm all ears if you care to explain in a few sentences where I'm wrong. I will say that when I finished the post, I was pretty unsatisfied with how clearly I worded everything, but I decided to click "Post" thinking it was adequate. obviously not... :lol:


In a nutshell, what motivated me to make the post is I have seen a number of big bore/short stroke motors with carefully matched combos put out very flat torque curves right in line with a regular stroker motor. All had heads that flow well with the smallest ports possible (AFR seems to be the best at this for out-of-box heads), about as much compression possible on 93 octane, generally a tight valve overlap to not bleed off as much compression as a wider overlap, and intakes ported to flow-match the heads. There's more to it, but these are the obvious factors.

I do understand the concept of leverage with longer strokes, but I think my point can be at least somewhat supported when you compare a Ford 5.4 2V and a 350 Vortec, both truck engines. One is a long stroke/small bore, and the other a big bore/small stroke, but they both have identical torque curves with the Chevy even having a slight advantage.

I'm leaving out alot of things and probably missed some, but do you get where I'm coming from?

Jason

A parallel universe?

Its the closest thing I see for this comparison.

Unless someone wants to build two identical engines, one with a longer stroke, and put them in one car and do tests for us. Doubt anyone will waste their money and time.

Everything is identical except the stroke in these two engines, as already I said. When one makes considerably more torque.....what would you say is the reason????

Do you think the 428 car has cement in the drive shaft or something and its a trick.

Its plain to see why the 422 makes more torque. Whats the big deal. I asked here to settle an agrument between some people. Everyone is wondering why the 422 has the 428 beat pretty good.

STROKE!!!!!

My, what a huge sample size you have..

Since this thread is going nowhere 'intellectually', i'll list some of my favorite (most comical) arguments thus far

1. The same engine builder built both engines using the same parts (yet somehow they have different bore/stroke and displacement)

2. The larger stroke engine made more power on a chassis dyno (mind you, no information about the driveline or vehicle... and using a chassis dyno is comical in itself for developing theories about bore/stroke)

3. 50lbs on a 1ft lever makes less torque than 50lbs on a 2ft lever (while this statement is true.. it has negligable relation to anything that should be discussed in this thread, not to mention the fact that he changed stroke, yet kept force constant!)

4. Comparing Ford 5.4L to a Chevy 350 vortec engine.. ( Were these built by the same builder as well? same parts? maybe...)

5. And in general... reading the proven statements on engine design... then resorting to Torque = force x distance...

Anymore that we care to add?

Seems some people don't understand that the art of engineering is in modeling the real world as accurately as possible, and then using that insight to PREDICT and EXPLAIN what has happened, what can happen, and what will happen under various combinations of circumstances.

Do you think it was just luck that all those Apollo moon trips ( particularly the first one ) got to the right place at the right time? ENGINEERING ! ! !

A parallel universe?

No, but I bet you were accused by some old fart once upon a time for being there before with this hobby. Haven't we all been there in some way? ;)

Jason

I can't beleive that for three pages of discussion there has been no mention of rod length and the effect it (and the stroke) has on dynamic compression ratio of the two engines. One of the two engines needs a different camshaft for optimal performance.

totally wrong... while the statement about 50lbf on a 2 foot lever arm making more torque than 50lbf on a 1 foot lever arm is CORRECT, you completely missed the fact that you dont have a constant force because for a given displacement, your bore is changing as well (i.e. decreasing the force in a porportional rate to the increase in lever arm)

What makes torque? Increasing the amount of chemical energy that can be released and utilized efficiently during a combustion event. So..

A. you can work on adding more air and fuel per event
B. you can work on increasing the efficiency of the event

Here is a copy of the chapter "Making Stroker Power" from the book "How to Build Big Inch Ford Small Blocks" by George Reid (his 6th published book out of 8, to date):
http://www.cartechbooks.com/cartech/contentfiles/204.pdf

For those who don't wish to read all of it:

"Stroking an engine does more than
just increase displacement. It increases
torque by giving the engine more of an
internal mechanical advantage. When we
increase stroke, we increase the engine’s
crankshaft arm or lever, which makes the
most of a combustion cycle. The longer
the stroke, the greater the torque or twist." pg.8

I eagerly await any replies disputing what Mr. Reid (an accomplished and respected author, as well as engine builder) has stated in one of his multiple books on the subject of engine theory and construction. I guarantee you he is well past his "one week".

I can't beleive that for three pages of discussion there has been no mention of rod length and the effect it (and the stroke) has on dynamic compression ratio of the two engines. One of the two engines needs a different camshaft for optimal performance.

Well first off Dynamic compression ratio is significantly "over played" on this website

Secondly, this thread cant get past Torque = Force x distance.. what make you think we could have a real discussion about engine design

and finally, rod length has much more impact on piston side load forces and rotating assembly inertia than it does on dynamic compression ratio.

Well first off Dynamic compression ratio is significantly "over played" on this website

Secondly, this thread cant get past Torque = Force x distance.. what make you think we could have a real discussion about engine design

and finally, rod length has much more impact on piston side load forces and rotating assembly inertia than it does on dynamic compression ratio.

I understand DCR is blown way out of proportion, but my point is that there is definitely a change in the characteristics of each engine other than the bore and stroke.

What? Torque = Force x Distance !!!! :bang:

Here is a copy of the chapter "Making Stroker Power" from the book "How to Build Big Inch Ford Small Blocks" by George Reid (his 6th published book out of 8, to date):
http://www.cartechbooks.com/cartech/contentfiles/204.pdf

For those who don't wish to read all of it:

"Stroking an engine does more than
just increase displacement. It increases
torque by giving the engine more of an
internal mechanical advantage. When we
increase stroke, we increase the engine’s
crankshaft arm or lever, which makes the
most of a combustion cycle. The longer
the stroke, the greater the torque or twist." pg.8

I eagerly await any replies disputing what Mr. Reid (an accomplished and respected author, as well as engine builder) has stated in one of his multiple books on the subject of engine theory and construction. I guarantee you he is well past his "one week".

Well.. the books i refer to for engine design are authored by Heywood and Taylor... NOT Mr Reid... Engines should be talked about in terms of BMEP, IMEP, PMEP, FMEP, BSFC, etc.. NOT "strokers do more than just increase displacement.. they increase torque becasuse of mechanical advantage.." If that is what Mr. Reid uses to explain engine design will stay away from his books..

and i'll be the first to say the statement made by Mr ried are misleading. He is correct, increasing the stroke of an engine does increase its torque. And YES the mechanical advantage is working. BUT what he did not mention is that he is also increasing displacement by increasing the stroke.

I will state that displacement is the reason for increased torque. If he decreased bore and increased stroke (i.e. keeping displacement the same) the torque should remain relatively unchanged.

Now the problem you run into with stroker engines is that the displacement to valve size ratio is becoming unfavorable. Which is why stroker engines usually have torque curves that are biased towards the low rpm range. If your looking for power for a given displacement a larger bore short stroke combination will always win. Why? because it can make equal torque to the stroker motor, but it makes that torque at a much higher rpm.. And in racing.. i'd rather have my torque at high rpm than low rpm..

No, but I bet you were accused by some old fart once upon a time for being there before with this hobby. Haven't we all been there in some way? ;)

Jason

Funny that you should mention that. I was extremely fortunate enough to hang around with, work with and be mentored by some very savvy OEM automotive engineers, many of whom were also into racing outside of the Company Super Duty programs.

At that time I mostly kept my mind open and my mouth shut. I like to think my mind is still open...and I learn a lot from my son about engines, but it's obvious my mouth is not shut. One of my mentors is quoted in my siggy. Hint, it's not Bo Darville (The Bandit) nor Bob Lutz who is only a few years older than I. I would dearly liked to have worked for him.

OK, when I was very young (about 12-13) and was taking apart my Dad's lawnmower engine to "soup it up", I could not understand how the flywheel magneto which rotated at engine speed of course, could create a spark only every other revolution. There was no internet where I could ask, and no one I knew to ask, so I struggled with it. I had never heard of "wasted spark", and it wasn't until years later that the Aha! moment occurred. That's about as far out as I ventured from the reality of how things actually work.

I'm all ears if you care to explain in a few sentences where I'm wrong.

Jason, no offense, but it would take volumes and many hours of teaching by someone who knows how engines work, and lots of studying by you to correct your ideas. First of all, you really don't think you are wrong, so you have no motivation to learn. Secondly, my read is that you want simple, spoon-fed answers to very complex concepts. It just doesn't happen that way, in spite of what many folks want to believe. To really understand the concepts, you need to know the "language" being used. That "language" is (primarily) physics which also involves math, statics, dynamics, fluid dynamics, thermodynamics, etc.

Not everyone understands those diciplines, which is perfectly fine. What's not fine is believing the incorrect bovine scat regularly dropped into forums such as this often by folks who have heard and believed the same scat from others. What is even worse is preaching that drivel to naive, gullible FNGs who hang out at places like this in an attempt to learn something. Their biggest challenge is determining who they should believe.

I offered you the opportunity to save some face in my first post, which you have not chosen to do. That's ok by me. I'm rarely a nice guy. You continue to step on your err....tie, so I guess you really don't give a scat what folks think of your knowledge.

FWIW: "tie" and "scat" are just nice ways to say "d!c&" and "sh!t" and not offend the mods or trip the "badword software". I told you I wasn't a nice guy.


You asked.


Jon

Extra credit homework question: Would you rather have an extra 20 horsepower at 2600 rpm or an extra 20 lb-ft of torque at 2600? Why?

Extra credit homework question: Would you rather have an extra 20 horsepower at 2600 rpm or an extra 20 lb-ft of torque at 2600? Why?


I'd rather have more stroke... because it increases power and torque EVERYWHERE




(sorry.. i could not help myself..:D)

I'd rather have more stroke... because it increases power and torque EVERYWHERE




(sorry.. i could not help myself..:D)

Let go of it for a minute and answer the question. :)

I can't beleive that for three pages of discussion there has been no mention of rod length and the effect it (and the stroke) has on dynamic compression ratio of the two engines. One of the two engines needs a different camshaft for optimal performance.

I posted this in post #31:

Engine Torque = (hm ) (hc ) (ht) (hv) (ra) (Vd) (N/2) (F/A) (Qhv) (1 / 4pi)

I believe that stroker engines may also have an impact on the hv (volumetric efficiency) term in the above equation. Stroker engines often have longer piston dwell times at the top and bottom of the cylinder, which allows more time for air and fuel to enter/exit the cylinder. This provides a better A/F charge and contributes to the power gains.

So while I may not have actually mentioned the rod length and/or camshaft specifically, the topic has been mentioned. The volumetric efficiency of the engine is indeed impacted.

The displaced volume term is the one most impacted by the increased stroke, which is the main focus here.
:nod:

So let's sum it all up and see if we can all come to some understanding:

Given bore does not change....(apples to apples)

1. Increasing stroke increases displacement of an engine.
2. Increasing displacement will always increase the torque output of an engine.
3. Lengthening moment on the rod journal is one method torque is multiplied.
4. Increasing distance of piston travel where an equal combustion force (pressure) is applied to the crank rod journal as compared to a shorter stroke multiplies torque.
5. Power is dependent on amount of torque created multiplied by rpm (divided by rpm constants for whichever you prefer, kw or hp)
6. Longer strokes move the effective powerband lower in the rpm range while increasing peak torque.

If anyone cares to add or delete or edit this list? Feel free to do so!

Now, changing bore completely changes all of this except for the fact that any increase in displacement increases torque output.

comments? (keep them civil, please.)

I posted this in post #31:



So while I may not have actually mentioned the rod length and/or camshaft specifically, the topic has been mentioned. The volumetric efficiency of the engine is indeed impacted.

The displaced volume term is the one most impacted by the increased stroke, which is the main focus here.
:nod:

You are correct, I missed your post.

Also, displacement of the two engines in post #1 are the same, so this is not the main focus.

I think that comparing the two engines with ONLY a different bore and stroke is wortless. Who says that the heads/cam used in the example engines are suited for both. I'm sure that you would see differences in power characteristics of a stock ls1 if you put a shorter rod in it. Same bore, same stroke, same cam and yet you will see a different power curve.

1. The same engine builder built both engines using the same parts (yet somehow they have different bore/stroke and displacement)

You need to read threads a little closer before you waste time posting.

Same brand parts you idiot, not the exact specs of each part. That would mean the engines would be exactly the same and this thread wouldn't be here. Top end is IDENTICAL though. What a clown.

2. The larger stroke engine made more power on a chassis dyno (mind you, no information about the driveline or vehicle... and using a chassis dyno is comical in itself for developing theories about bore/stroke)

I said they are both M6's. Both F-Bods. I don't know if one of them has a Moser 12 bolt, but one of them does. Gears are the same in both though, thats what matters.

Noone is trying to develop theories about anything, when 2 cars dyno differently there's always a reason. When a smaller cubed engine makes MUCGH more power and torque then another one that is bigger cubed....its interesting to know why, especially when there is only one thing different about the two engines. STROKE!

Anymore that we care to add?

Yes, just because the thread didn't stop at your first post because you think you're GOD and answered the question clearly, don't take it so personal that others explain things so much better than you do.

I can't beleive that for three pages of discussion there has been no mention of rod length and the effect it (and the stroke) has on dynamic compression ratio of the two engines. One of the two engines needs a different camshaft for optimal performance.

Too many people here think they know the answers, but really its just BS coming out of their mouths.

Thats the problem.

and i'll be the first to say the statement made by Mr ried are misleading. He is correct, increasing the stroke of an engine does increase its torque. And YES the mechanical advantage is working. BUT what he did not mention is that he is also increasing displacement by increasing the stroke.

You rode the short bus to school didn't you. He did mention it, first damn sentence in the quote. Jeezus Kee-Riced.

"Stroking an engine does more than
just increase displacement. It increases
torque by giving the engine more of an
internal mechanical advantage.

Holy shit!! Did I call it, or what?! :lol:




One probably had a 10 bolt and the other a 12 bolt. :)

I don't know which one of them has a Moser 12 bolt, but one of them does. Gears are the same in both though, thats what matters.





:D

Holy shit!! Did I call it, or what?! :lol:

:D

Not really, the other one has a Strange 12.

That doesn;t make a difference in hp/tq anyway, so who cares.

How is it that someone who is obviously wasting their time in this section was able to get so much more information replied than many I've seen who can actually comprehend at least some of what has been typed? :lol:

I'm glad some of you wasted your time, because it's always good to read, but it's an exercise in futility.

Old SStroker- I'll take the 20 hp please :D

Old SStroker- I'll take the 20 hp please :D


You get partial credit. Answer the "Why" for full credit. :)

You rode the short bus to school didn't you. He did mention it, first damn sentence in the quote. Jeezus Kee-Riced.

"Stroking an engine does more than
just increase displacement. It increases
torque by giving the engine more of an
internal mechanical advantage.

Well you telling me that i rode the short bus is quite comical...

I really should not dignify this with a response.. but i will.

What i should have said is that he leads you to believe that the displacment increase is not as important as the "mechanical leverage" This statement gives all the readers the wrong impression as to why the torque is increasing. Thus leading to the argument in this entire thread.

His statement (based on how i read it) leads me to belive that Displacment increases torque.. but Stroke increases torque EVEN MORE! like some sort of torque multiplier (which is wrong). So the average joe reading it.. says, "hey i understand, if i have a wrench that is 1 ft long.. i have more leverage with a 2 ft long wrench.. by golly.. i get it!!"

When people try to simplify the world to the mental capacity that they have.. A LOT of things get assumed... and many of those things are WRONG!!

HP = torque x RPM/5250

So to make 20 more HP at 2600 RPM requires an RCH over 40 ft-lb of torque.

Getting 20 ft-lb more torque at 2600 RPM yields only an RCH (:confused:) under 10 HP.

Hence: I will take 20 HP at 2600 RPM, please.


Extra extra credit: Identify the unit "RCH" :devil:

HP = torque x RPM/5250

So to make 20 more HP at 2600 RPM requires an RCH over 40 ft-lb of torque.

Getting 20 ft-lb more torque at 2600 RPM yields only an RCH (:confused:) under 10 HP.

Hence: I will take 20 HP at 2600 RPM, please.


Extra extra credit: Identify the unit "RCH" :devil:

Correctamundo, Kid!

In measurement lab in college, we did a scientific study of the actual size of a RCH. .0014 +/- .0001 in. dia, if I recall. Obtaining samples to measure was the fun challenge. Real redheads were few and far between in Flint Michigan. ;)

The youngsters here STILL don't know what the RCH unit is. When one of my college profs at Case Tech in Cleveland told us that the modulus of elasticity of steel was just an RCH under 30,000,000 psi, we cracked up that he would use it in a lecture.

OK, in 1965 this was a big deal :nod:.

The youngsters here STILL don't know what the RCH unit is. Some do but probably only if they hang around with us old fossils.

OK, in 1965 this was a big deal :nod:.

GMI '66

We went to different schools together.

Jon

:lol: I've heard the unit of CH used many times, but never red

I used 2626 rpm instead of 2600 so, no CH needed....

HP = torque x RPM/5250

So to make 20 more HP at 2600 RPM requires an RCH over 40 ft-lb of torque.

Getting 20 ft-lb more torque at 2600 RPM yields only an RCH (:confused:) under 10 HP.

Hence: I will take 20 HP at 2600 RPM, please.


Extra extra credit: Identify the unit "RCH" :devil:

I am assuming this RCH "Measurement" is something similar to the "Pube" measurement? lol

"H" in ANY color is rare these days, with the younger generation. :)

ok so.. different engine parts.. different rear ends.. but everything is the same and only the stroke is different..gotcha..

so it's GOT to be the stroke says the guy who can't even tell when there's an increase in frictional loss in a bigger gearset (typically)..

maybe the "top end" that both share is more advantageous to the smaller bore/longer stoke.. maybe the head starts to stall out a bit on the bigger bore..

so many variables.. there is no way to take this one example and say it applies in every case.

Not really, the other one has a Strange 12.

That doesn;t make a difference in hp/tq anyway, so who cares.

ok so.. different engine parts.. different rear ends.. but everything is the same and only the stroke is different..gotcha..

so it's GOT to be the stroke says the guy who can't even tell when there's an increase in frictional loss in a bigger gearset (typically)..

maybe the "top end" that both share is more advantageous to the smaller bore/longer stoke.. maybe the head starts to stall out a bit on the bigger bore..

so many variables.. there is no way to take this one example and say it applies in every case.

We are talking about engine torque, where and how, stroke and bore have effect on it. The ring gear friction would be a good variable in a drivetrain loss arguement but is irrelevent in this thread.

We are talking about engine torque, where and how, stroke and bore have effect on it. The ring gear friction would be a good variable in a drivetrain loss arguement but is irrelevent in this thread.

There is a heck of a lot more irrelevant stuff in this thread. :)

I wrote a bunch of it.

Subscribing for entertainment value... ;) ...is it ok for me to do that...

Subscribing for entertainment value... ;) ...is it ok for me to do that...

You better ask Patrick G., your friendly neighborhood moderator.

Anyone know why his name is always in red?

"LS1 Tech Administrator"

"LS1 Tech Administrator"

A-hah! The "Head MFWIC"?

Hey all,

I was bored and reading this thread and it caught my attention.

I laugh at the people here that say because it has a bigger stroke it will make more torque period... in a static world that would possibly be true.

Now I know NOTHING about engine design. I'm a degree'd engineer from Purdue, but specialized and work in the Hydraulic industry so i'm not going to sit here and claim I know jack shit about engine design. But I thought I would throw out a few things as I have recently taken a interest in the field: (and wish I would have taken those engine design classes... :()

1) At the instantaneous combustion "time", it doesn't matter if you have a 3.48" stroke or a 5' stroke; as you technically have no leverage at this point. If you have a given cylinder bore the downward force will be the same no matter the stroke. But in the example of a "fixed" displacement the larger bore will have a larger force at that "moment" then the smaller bore.

2) As the cylinder travels down the bore the pressure will decrease and the force exerted on the piston will decrease as well. But the larger piston will still have a greater force then the smaller piston.

3) As the cylinder travels down the bore the longer stroke engine will gain more "leverage" in a larger moment arm then the smaller stroke.

4) More of an interesting point of conversation... at the point of the next cylinder firing (90 deg); the moment arm of the "stroke" will be at it's greatest point even though the pressure in the cylinder is at its lowest. How does this torque compare to the cylinder that is firing at that exact same moment?

5) What is the frictional losses of moving the piston faster down the bore compare to a slower speed?

To these answers I will admit I have NO CLUE. I would have to do countless hours of research, testing, etc... to even give somewhat of a "educated" estimate. I just thought I would throw some of these out there to people that believe this is a cut and dry "longer stroke=more torque" static type of situation. This is a VERY dynamic system, and not just dynamic on one front; but multiple fronts.

So I suggest listening to the people that have the knowledge AND the experience in giving the best answer for this type of a question as this is nothing that can be even remotely explained on an internet message board.

few things that caught my attention reading this,

#1 454cid 4.125" bore 4.250" stroke
#2 454cid 4.185" bore 4.125" stroke
#3 422cid 4.030" bore 4.125" stroke iron block more tq/hp than #4
#4 428cid 4.125" bore 4.000" stroke alum block

a#1) the comparison made between the 2 engines 422 and 428 cid. the main focus was on bore & stroke and a general statement of everything else was the same was made. Everything else was not the same... the cam specs were never mentioned and only the statement was made that they were both in the 230's duration range.

b#2) And i'm assuming it was a chasis dyno giving the output numbers of the 422 vs the 428 since you mentioned both had M6 transmissions. Biggest problem I have with going off any kind of dyno numbers is they are not accurate and almost never comparable, there are too many variables never accounted for, oil temps can be a big factor and they are never monitored, no mention was made to when the dyno's of the 2 motors happened, if they weren't back to back then what was the temperature, humidity, barometer difference? Was the 428 done in the afternoon, the 422 in the evening after the temperature dropped?

c#3) the engine tune get's it's own line, the tune was never mentioned and do you know what the a/f ratio was for each engine? At this point I simply can't put any faith in your claim the 422 (greater stroke) made more power than the 428, and I certainly would not draw the conclusion the stroke was the cause of the extra power !

d#4) disputing Mr. Reid and Making Stroking Power page 8, yeah theoretically there's an increase in leverage so you can say a greater torque or twist. Does he bother to do the math and show that a 1/8" increase in stroke is only 1/16" an increase in moment arm? tq = f * d means it's a linear relationship, on a 4" stroke vs a 4.125" stroke that's a moment arm change of 2" vs 2.0625", only 3.125% and 3% of 400 lb-ft is only 12 lb-ft ! sad, i don't think i'll be buying that book, this just goes to show how nobody thinks anymore. In fact, if you do the math comparing this change to the change is piston surface area (bore change) you will find another linear relationship happening: pressure (pounds per square inch). Using a 4" bore and 4" stroke, going up X" in stroke and decreasing same X" of bore (neglecting actual piston surface area) they cancel out, how about that! Hmm, maybe other things are happening influencing power output and it's not just about stroke and bore?

e#5) the engine with the longer stroke will end up making more power because you have the same amount of pressure from the air/fuel being burned pushing down on the piston. completely neglects the whole point of mean effective pressure (keyword mean) because as the piston moves downward volume increases and pressure decreases, also see d#4.

f#6) the iron vs aluminum block may very well matter, I don't know how relevant it is at 500 hp levels which was stated, but if you get cylinder distortion you will definitely lose power and I think it would be more likely in an aluminum block with liners vs an iron block.

g#7) and 20 more horsepower @ 2600 rpm being a RCH over 40 lb-ft of torque is correct, however 20 lb-ft of tq @ 2600 rpm is a BCH under 10 hp. A red hair is thicker meaning greater, a blonde is thinner meaning smaller.... you fag :lol:

I'm no engine builder, but we can look at this from a math/physics POV:

- always keep in mind that force = pressure x area where pressure is proportional to displacement and VE (is that right...?) and varies as combustion progresses;

- the force component along the connecting rod may be less than the force on the piston because the rod may be at an angle from vertical; when the rod is vertical, the force component along the rod equals the force on the piston; when the rod is angled, the rod's force component quickly reduces as the crank turns further from TDC;

- when the force on the piston peaks, the rod is not perpendicular with the crank arm, which means the crank moment arm is effectively shortened; when the rod is vertical, the moment arm has zero length; when the rod is angled, the effective moment arm increases with crank angle, but the force component has already reduced quite a bit;

- increased stroke produces greater peak piston velocity (and mean pistion speed also) (see my example graph derived from applying calculus to crank-rod geometry), which improves VE if the heads can flow (would you agree...?); and improved VE produces greater peak combustion pressure; this would be greater than the pressure produced by displacement alone (i.e. same stroke or bigger bore).

- something to consider is that increased piston velocity means increased frictional losses since friction increases with velocity, but as you can see in the graph the increase is more substantial closer to the velocity maxima/minima (i.e. when velocity is furthest from zero crossings) and is not as substantial near TDC/BDC;

What can we conclude: torque is not influenced by crank radius moment arm [stroke] as it is by displacement [stroke x area] and VE.


(I can also graph for offset pistons, those are interesting.)

http://img300.imageshack.us/img300/2668/crankradiusvariestn5.png


Angular velocity (omega) [rad/s] = w = 2 * pi * rpm / 60

To convert velocity [inch/rad] to velocity [inch/s] mulitply by w.
To convert acceleration [inch/rad^2] to acceleration [inch/s^2] multiply by w^2.

:zzz:

You mentioned piston offset, I was wondering why it is seldom talked about?
so in your example;

if L=6.125" the 4.125x4.25" stroke, with a .25" offset

how would that compare to

L=6.125" the 4.185x4.125" stroke, no offset.

Does piston offset have any benefit for power/slap/friction, ??

Here's a graph I previously made showing what offset does to piston velocity and acceleration (+/- 0.5" is a bit extreme):


http://img296.imageshack.us/img296/6171/l6r2kxai6.png


K > 0 is toward "after TDC" (i.e. same direction crank spins);
K < 0 is torward "before TDC" (i.e. toward major thrust side);

I'll make you a set of graphs tomorrow.

Yep the biggest thing to remember is power is a function of the stroke length, bore size, RPM, and the average cylinder pressure during the combustion stroke. The longer stroke has a greater influence on the average cylinder pressure.

Also don't forget, if you double the power a motor makes you'll only increase the peak cylinder pressure by about 20% so that's some food for thought. As the piston travels downward it's still burning the fuel mixture. Timing and the type of fuel used can greatly alter these charicteristics

displacement = torque /more displacement = more torque

If 2 engines have the same displacement but stroke is different , both engines will make the same torque.

displacement = torque /more displacement = more torque

If 2 engines have the same displacement but stroke is different , both engines will make the same torque.

Wow, just wow. Did you read any of the posts before yours? That statement is a little simplified, don't you think?

Wow, just wow. Did you read any of the posts before yours? That statement is a little simplified, don't you think?

Nope. It's pretty damn close, and summarizes things quite well.

You are a big-ender as Jonathan Swift would say. Sorry for the obscure literary reference, but I think it applies. Gulliver's Travels (big hint) is one of my favorite stories.

Jon

Nope. It's pretty damn close, and summarizes things quite well.



I agree.... but will add that displacment = torque... or basically the ability to make torque.

Bascially just because you have a certian displacement doenst mean you will make a certain torque value.. but you only have the abilty to make so much torque NA per displacemnt.

Most engine builders dont have the ability to achive maximum torque vs. displacement.. but there is a limit.. and its around 13 bar bmep.. i have seen more and i have seen less...

I agree.... but will add that displacment = torque... or basically the ability to make torque.

Bascially just because you have a certian displacement doenst mean you will make a certain torque value.. but you only have the abilty to make so much torque NA per displacemnt.

Most engine builders dont have the ability to achive maximum torque vs. displacement.. but there is a limit.. and its around 13 bar bmep.. i have seen more and i have seen less...

I think it's higher than that, DanO. Current F1 NA engines have a BMEP about 15.1 bar at power peak rpm, and somewhat higher at torque peak. The real stars are the 500 cube ProStock NA engines with over 16.5 bar BMEP at power peak rpm. Even Engine Masters Challenge engines achieve about 14 bar @ 6500 almost every year.

Maximum NA BMEP (@ power peak rpm) hasn't improved a lot in the fairly recent past even as hp/L (or per cubic inch for those of us who don't think metric) continues to improve as engine folks are able to hold the BMEP at ever higher rpm. That indicates (pun intended) to me that IMEP is being improved, or at least friction and pumping losses continue to be reduced.

There is a considerable gap between the theoretical ability to produce torque (BMEP) and that actually produced by most builders.

I think we are preaching to the choir here, however. The rest aren't buying it. More's the pity.


Jon

I think it's higher than that, DanO. Current F1 NA engines have a BMEP about 15.1 bar at power peak rpm, and somewhat higher at torque peak. The real stars are the 500 cube ProStock NA engines with over 16.5 bar BMEP at power peak rpm. Even Engine Masters Challenge engines achieve about 14 bar @ 6500 almost every year.

Maximum NA BMEP (@ power peak rpm) hasn't improved a lot in the fairly recent past even as hp/L (or per cubic inch for those of us who don't think metric) continues to improve as engine folks are able to hold the BMEP at ever higher rpm. That indicates (pun intended) to me that IMEP is being improved, or at least friction and pumping losses continue to be reduced.

There is a considerable gap between the theoretical ability to produce torque (BMEP) and that actually produced by most builders.

I think we are preaching to the choir here, however. The rest aren't buying it. More's the pity.


Jon

Agreed... thats why i said i have seen more.. but more often i see less than 13bar. You are talking about engines that are well made, there arent alot of average engines above 13bar

and yes all of the advancements are trying to get that high BMEP at higher RPM.. those F1 guys always amaze me. although, personally, i wish they would go back to boosted engines... maybe drop down to 1.0L? but i digress..

anyways.. we need to keep in mind the fuels being used... many different energy contents and air fuel ratios... cant really engines if one is running nitromethane and the other is running 87 octane.. For sake of this discussion, i'd stick to 93 pump gas

How in the hell are we still arguing about this?! :lol:

You guys are racing calculators. Kind of like racing dynos.