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.

 

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 .

 

https://ls1tech.com/forums/advanced-engineering-tech/1006863-ic-engine-power-torque-equations.html

 

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

 

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.

 

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.


.

 

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.

 

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.

 

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 ). 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.

 

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

 

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!

 

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.