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Old 08-11-2016, 02:48 PM   #1
George Bryce
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Default How much power per inch can you make with...

There are many good, talented and accomplished engine builder/designers on this forum. This is my "go to" place for good answers.
As title asks, how much power per cubic inch do you think could be made with a 2 cylinder, stay with me here, a 640 cubic inch "Pro Stock" version, BUT, the front two cylinders, only, no 8 cylinders helping, just two pistons.???

Right now we use two 5.127 bore pistons, 3.875 stroke, 2.75 intake valves, 2.00 exhaust valves, .600 lobes with 1.85 rocker ratio. 8.6 long pushrods.
We turn it 10,000 rpm. We run EFI. We are allowed one injector per cylinder.
We run it from 8,000 to 10,000 rpm.

I believe we can get to 400 HP, not there yet. But when we do get there, that will only be 2.5 HP per inch. I think it is because there is not much help to rotate the crank with only two cylinders firing. If the rotation load was shared by 8 cylinders, it could make a lot more per inch.

This NHRA two cylinder is 160 cubes.....if it was a V 8, it would be a 10,000 rpm 640 cubic inch engine. I would love to hear and see your ideas and comments....this will be a technical sharing forum please.

Thanks!!!!
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Last edited by George Bryce; 08-11-2016 at 02:49 PM.
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Old 08-11-2016, 03:08 PM   #2
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Default Re: How much power per inch can you make with...

Are you limited to 10,000? How much does your piston and rod combo weight? Do you have a common plenum or individual runners and throttle bodies?

Last edited by E.R. Racing; 08-11-2016 at 03:09 PM.
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Old 08-11-2016, 03:49 PM   #3
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Default Re: How much power per inch can you make with...

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Are you limited to 10,000? How much does your piston and rod combo weight? Do you have a common plenum or individual runners and throttle bodies?
Great questions.
We can rev it till it blows.
Individual runners with 3.3 throttle bodies, like F1 cars
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Old 08-11-2016, 04:22 PM   #4
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Default Re: How much power per inch can you make with...

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Originally Posted by George Bryce View Post
Great questions.
We can rev it till it blows.
Individual runners with 3.3 throttle bodies, like F1 cars
Would more RPM not produce an opportunity for more hp?
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Old 08-11-2016, 04:36 PM   #5
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Default Re: How much power per inch can you make with...

On Jon Kasse's web site they advertise his 820 Ford hemi as making 1900 plus hp at what rpm (?) and that's a little over 2.3 hp/cuin, so if you can source the parts to be able to run the same bore stroke as you are along with the same size valve sizes, 2.5hp/cuin is not out of the question. But with a smaller bore/valve size and longer stroke it would be harder to do so. Most of RM's larger standard type engines are around 2 hp/cuin, some a little more or little less.

4 times the cyl's friction start to add up fast at 10000 rpm.
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Old 08-11-2016, 04:38 PM   #6
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Default Re: How much power per inch can you make with...

Absolutely, we are trying to be able to turn it more.....we run over parts over 10200, so far.
We are addressing the weakest links everyday. But 65875 average piston speed at 10200 is hard on parts
With 600 gram pistons.....over 5 and an eight inches bore.
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Old 08-11-2016, 04:50 PM   #7
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Default Re: How much power per inch can you make with...

lol 5-1/8" bore ... great thread something i have always wondered myself .......
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Old 08-11-2016, 04:59 PM   #8
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Default Re: How much power per inch can you make with...

This older 730 Hemi head nitrous build (no nitrous) made 2.2 hp/cuin at 8000 rpm.

http://www.maxracesoftwares.com/foru....php?f=5&t=246
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Old 08-11-2016, 05:01 PM   #9
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Default Re: How much power per inch can you make with...

George saw the prior post on the bottom end.

Are you guys required to run the pickle fork rod or is it just a function of the rule requiring the cylinders to be inline?

I am not an engineer/engine builder and this may be a stupid question but.... If the rule is the latter, has anyone ever tried run conventional rods with an offset to allow a one piece crank and to get rid of the pickle rod?
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Old 08-11-2016, 05:21 PM   #10
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Default Re: How much power per inch can you make with...

That's a lot of bore to get a flame front to run across at 10,000 rpm

Plug location....I am sure you are central located
Fuel....am sure you are restricted to blend
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Old 08-11-2016, 05:30 PM   #11
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Default Re: How much power per inch can you make with...

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That's a lot of bore to get a flame front to run across at 10,000 rpm

Plug location....I am sure you are central located
Fuel....am sure you are restricted to blend
Yes Sunoco SR-18 by rules.
We run 2 plugs per cylinder.
We do have to run the Knife and Fork/ Male and female rod set up.
Because S&S thought it needed to be a version of the Harley engine, XLCH.
Harley team runs automotive side by side rods, I think.
Our engine is inline front to rear....
The new Victory engine that is up for approval is side by side, again I am told.
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Old 08-11-2016, 06:31 PM   #12
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Default Re: How much power per inch can you make with...

Quote:
Originally Posted by George Bryce View Post
Absolutely, we are trying to be able to turn it more.....we run over parts over 10200, so far.
We are addressing the weakest links everyday. But 65875 average piston speed at 10200 is hard on parts
With 600 gram pistons.....over 5 and an eight inches bore.
600 grams seems unusually heavy.... To me.
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Old 08-11-2016, 06:36 PM   #13
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Default Re: How much power per inch can you make with...

Quote:
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600 grams seems unusually heavy.... To me.
For 5-1/8" bore? I was thinking it was pretty light, and still stays together.
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Old 08-11-2016, 06:37 PM   #14
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Default Re: How much power per inch can you make with...

If you had a firing order which you could build a scavenging ex system, how much more do you think it would help"?
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Old 08-11-2016, 06:58 PM   #15
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Default Re: How much power per inch can you make with...

2 Cylinders,Very little power overlap,lots of time between firing cycles.Its pretty impressive what George has accomplished and his relentless pursuit to find more.Bill C.
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