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Re: short stroke vs long stroke [Re: Sport440] #1129946
12/09/11 02:25 AM
12/09/11 02:25 AM
Joined: Jul 2010
Posts: 2,091
Delray beach, Florida
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Performance Only Offline
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Joined: Jul 2010
Posts: 2,091
Delray beach, Florida
Quote:

Your right Cab, Coomer mispoke, that will happen.

To the original question, in most cases, with the same CI, The bigger bore is the way to go.

Technically, with the same PSI combustion pressure, both equal CI engines would produce the same output if the A/F intake charge would remain the same.

But typically the heads are always shrouded by the bores with the production motors that we use for racing. Therefore, the bigger bore will always rule VS longer stroke Same CI.

It will have a lessor effect on a smaller HP motor say 500 HP and a much larger effect on say a 900 HP motor.

Dogday, and others good posts.




i have to agree.
aside from that, in the real world nobody would build one of each with identical parts anyway, would they?


machine shop owner and engine builder
Re: short stroke vs long stroke [Re: MR_P_BODY] #1129947
12/09/11 03:02 PM
12/09/11 03:02 PM
Joined: Jan 2003
Posts: 27,421
Balt. Md
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383man Offline
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Joined: Jan 2003
Posts: 27,421
Balt. Md
Quote:

For racing I would go with bore... but for the street
I would go stroke due to the rpm factor and the leverage






I agree with this alot on street/strip cars. I mean cars in the 3600 to 4200 lb class where you need to get alot of weight moving fast. Seems most favor the longer stroke engines for the low rpm torque. One reason I went with a longer then the stock 3.75 stroke as I wanted my 3700 lb car to tap 10's without pushing 7000 rpm. Ron

Re: short stroke vs long stroke [Re: Performance Only] #1129948
12/09/11 04:11 PM
12/09/11 04:11 PM
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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BradH Offline
Taking time off to work on my car
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Taking time off to work on my car
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Val-haul-ass... eventually
Quote:

... in the real world nobody would build one of each with identical parts anyway, would they?



Does a Chevy-oriented magazine count? IIRC, I may still have copy of one where they actually built two versions of the same SBC engine, one as a 383 (3.75" stroke + stock bore) and the other as a 377 (stock stroke + big bore) to see the outcome. (Even the same cam was used, which IMO means if it was "right" for one of them, then it was also "wrong" for the other. )

The two engines performed pretty much as people would expect w/ the 383 making more torque and the 377 pulling a little more peak HP. From what I recall, the differences weren't major, yet fairly predictable.

Re: short stroke vs long stroke [Re: Cab_Burge] #1129949
12/09/11 04:24 PM
12/09/11 04:24 PM
Joined: Nov 2003
Posts: 6,293
Rock Springs
Bob_Coomer Offline
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Bob_Coomer  Offline
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Joined: Nov 2003
Posts: 6,293
Rock Springs
Quote:

Quote:


I turn a 4.5 stroke 8K with a set of 440-1's. I know a 4.15 stroke will go that too. The 4.5 stoke has way way more cycles per minute, which wears out parts though.
I know this to be true, despite what the text book racers may think.


Bob, are you sure that what you wrote is what you meant? RPM are RPM regardless of stroke, 5000 RPM is 5000 RPM with two inch stroke or a four inch stroke The ring and piston travel, distance traveled, is more on a long stroke motor than a short stroke motor 5000 RPM on a two inch stroke motor equals 10,000 inches per minute, the four inch stroke motor rings will travel 20,000 inches in the same minute Not trying to start or make a war, just trying to make sure what we are discussing is accurate and understood the same by all readers



Yea thanks for clarifying, I got it backwards guys... I get into a hurry and dont proof read none..
Just to clarify my point.
Stroke or Bore size has little effect on peak rpm, compared to the impact of head volume. People do NOT select bore size in reguards either...
Most go with the largest bore size possible cause we know it helps. I think Bore Vs stroke, bore is the clear winner. We usually start with 3.75" of stroke as a baseline. Stroker cranks are had now it just doesnt cost hardly any more to build a bigger engine, so...
I think the engine I outlined before is relevant, there is lots of guys with flat tappet cams and Indy heads, lots and lots more than larger- big bore, long stroke engines.
It falls back on the availability and cost of a aftermarket block. 90% of Mopar bracket racers are still using stock blocks. So figure bore size range from 4.32-4.375.. Which leaves stroke to increase cubic inches. I think the 4.25 stroke is "Best" along with the largest bore size possible.
This coming from a guy who's last two engines where 4.5 stroke, large bore aftermarket block engines. So Im not exactly speaking out of my butt here. These engines arent dyno queens, or test beds for bolt on parts....
matter of fact they were NOT dyno tested at all. Only numbers that matter to me is the ones they generate shortly after they are first fired at the local track.
The engine Im slowly slapping together will be the largest bore possible with a aftermarket block, and a 4.25 bottom end..
I believe it to be more effective than my previous setups, when you look at HP per cubes.

Last edited by Bob_Coomer; 12/09/11 04:28 PM.

[color:"red"]65 Hemi Belvedere coming soon [/color]
[color:"#00FF00"]557" Indy engine 1.07 60ft 144mph in the 8th 2100 lbs package [/color]
Re: short stroke vs long stroke [Re: BradH] #1129950
12/09/11 04:39 PM
12/09/11 04:39 PM
Joined: Nov 2003
Posts: 6,293
Rock Springs
Bob_Coomer Offline
master
Bob_Coomer  Offline
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Joined: Nov 2003
Posts: 6,293
Rock Springs
Quote:

Quote:

... in the real world nobody would build one of each with identical parts anyway, would they?



Of coarse not, thats the point... This is the type of engine that 90% of the racers are building though, so it matters plenty...
.
Quote:


Does a Chevy-oriented magazine count? IIRC, I may still have copy of one where they actually built two versions of the same SBC engine, one as a 383 (3.75" stroke + stock bore) and the other as a 377 (stock stroke + big bore) to see the outcome. (Even the same cam was used, which IMO means if it was "right" for one of them, then it was also "wrong" for the other. )





The two engines performed pretty much as people would expect w/ the 383 making more torque and the 377 pulling a little more peak HP. From what I recall, the differences weren't major, yet fairly predictable.




Thats why I think lots of the magazine articles are for entertaining purposes only. Fact is you probably couldnt tell one engine from the other on the time slip, in the same car, same day. The dyno is a good tool, but really doesnt tell how the car will perform at the track.

Last edited by Bob_Coomer; 12/09/11 04:40 PM.

[color:"red"]65 Hemi Belvedere coming soon [/color]
[color:"#00FF00"]557" Indy engine 1.07 60ft 144mph in the 8th 2100 lbs package [/color]
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