XtraCajunSS

iTrader: (2)

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.

Shane

Camaro99SS

iTrader: (4)

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...


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

Old SStroker

A parallel universe?

KMS.1320

iTrader: (1)

My, what a huge sample size you have..

DanO

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?

Clevite Kid

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 ! ! !

Camaro99SS

iTrader: (4)

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

speed_racer

iTrader: (2)

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.

Dan Stewart

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/...tfiles/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".

DanO

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.

speed_racer

iTrader: (2)

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 !!!!

DanO

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..

Old SStroker

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.

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 "****" 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?

DanO

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




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

Old SStroker

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

JohnnyC

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.

Dan Stewart

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.)

speed_racer

iTrader: (2)

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.

spoolit

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.

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!

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.

spoolit

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

Thats the problem.