Ideal compression ratio for Centri setup

[eLeSthree]

I cant really swing a new short block having just bought a new house and the remodeling that comes with it. So in order to crank this thing up a notch, I'm going the least expensive route, and gonna drop some pistons and rods into my stock block/crank.

I'm pretty sure I'm going with Wiseco, but I don't know what compression to shoot for.

I'm looking for a reliable weekend/street/track car that makes around 1000whp.

My options in 4.07 bore are -3.2cc and -11cc. Where will those pistons land me compression wise?

Which is most ideal for a centrifugal supercharger setup?

Since I have a tight budget, should I go with an H beam, or even a Scat I beam?

[hou30guy]

Probably some where around 10.3 to 10.5 depending on cam bleed ofd to around 10.0

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[Omega]

What kind of fuel?

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[eLeSthree]

Originally Posted by Omega

What kind of fuel?

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E85. Its about 77% locally and easy to access.

[eLeSthree]

Originally Posted by hou30guy

Probably some where around 10.3 to 10.5 depending on cam bleed ofd to around 10.0

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So dont give up much. Will the -3cc piston get me there?

[Omega]

10.5 will be fine.

There is a little more to it than the piston dish CC. Heads and gasket thickness are two pretty big factors. A good shop will be able to make/order pistons to give you the exact CR you want rather than having you select two options that yeild a pretty substantial difference in CR.

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[eLeSthree]

Originally Posted by Omega

10.5 will be fine.

There is a little more to it than the piston dish CC. Heads and gasket thickness are two pretty big factors. A good shop will be able to make/order pistons to give you the exact CR you want rather than having you select two options that yeild a pretty substantial difference in CR.

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Shop? You’re looking at him. I have a machinist, and a tuner, but everything else is on me. I was basing the compression off the stock ls3 head and gasket. Should have mentioned that. I figured this has been done 100 times already.

Ill find a calculator and the ls3 head specs. Thanks.

[realcanuk]

Don't want to sound like a dick, but a reliable 1000 hp street /track car on a tight budget doesn't really exist.

[eLeSthree]

Originally Posted by realcanuk

Don't want to sound like a dick, but a reliable 1000 hp street /track car on a tight budget doesn't really exist.

I can accept that. Ill be happy with 900whp street car that doesnt see much track time. If it breaks, I’ll fix it. The stock motor has taken 800whp so far, so with forged pistons and rods, 900 is feasable.

I found a compression calculator. With a 4.07 bore, 4.08 gasket hole, .051 gasket thickness, 68.5cc head, 3.622 stroke, and a -3.2cc piston sticking out .005, I’ll be at 10.46. The -11cc piston yielded 9.6.

Going with -3.2cc. Thanks

[hillshooter]

Originally Posted by eLeSthree

I can accept that. Ill be happy with 900whp street car that doesnt see much track time. If it breaks, I’ll fix it. The stock motor has taken 800whp so far, so with forged pistons and rods, 900 is feasable.

I found a compression calculator. With a 4.07 bore, 4.08 gasket hole, .051 gasket thickness, 68.5cc head, 3.622 stroke, and a -3.2cc piston sticking out .005, I’ll be at 10.46. The -11cc piston yielded 9.6.

Going with -3.2cc. Thanks

I have been playing with this question for 2 years. I built an engine with around 11.3:1 compression, turbo. Made stupid power on low boost and had sick midrange. Almost unbelievable power for Boost numbers, like 900HP on 12-13 pounds. Problem is I would get to the track and actually load the car and it wouldn't rev out, tons of detonation issues, tried plugs all the way to an 8 heat range, changed several fuels and eventually went to Ethanol, none of that solved it, could pull timing and get it to live but would be noticeably down on power.

This year I have a new motor I am running and it will be 10:1. of course I am convinced its going to work better but we will see!

To sum up and answer your question, I would say if I was building an application for the street and wanted to run 8-10 pounds of boost I would try for 11:1. However if you wanted to see some RPM and some serious boost like 15-20 then lower is better.

PS: LS9 gasket is .054 thick and that's what I run, also stock ls3 chamber should be 68. I have as close to a zero deck height as possible.

[Ajax2112]

Originally Posted by hillshooter

I have been playing with this question for 2 years. I built an engine with around 11.3:1 compression, turbo. Made stupid power on low boost and had sick midrange. Almost unbelievable power for Boost numbers, like 900HP on 12-13 pounds. Problem is I would get to the track and actually load the car and it wouldn't rev out, tons of detonation issues, tried plugs all the way to an 8 heat range, changed several fuels and eventually went to Ethanol, none of that solved it, could pull timing and get it to live but would be noticeably down on power.

This year I have a new motor I am running and it will be 10:1. of course I am convinced its going to work better but we will see!

To sum up and answer your question, I would say if I was building an application for the street and wanted to run 8-10 pounds of boost I would try for 11:1. However if you wanted to see some RPM and some serious boost like 15-20 then lower is better.

PS: LS9 gasket is .054 thick and that's what I run, also stock ls3 chamber should be 68. I have as close to a zero deck height as possible.

Very good advice!!

I would go with the -11 cc. At 9.6 your in a safer area to add more boost. If your ever wanted to step up the compression a little you could always deck the heads or go with thinner gaskets to raise the compression which is a lot less work and cheaper option then having to change pistons. I have had bad experiences using thicker gaskets to lower compression.

[mrimpala02]

This has been discussed many times before.

From all of my research I would suggest the 10-10.5:1. I think less than that is leaving too much on the table and more than that can cause too many issues as Hillshooter pointed out.

[Slowhawk]

10.5-1 is good. Most of our boost motors run that.

[SSE 4 2SS]

My motor is 10.5-1, 3.9 stroker. Twin 76/75 CEA turbos... As hillshooter mentioned, it makes stupid power, 1200 RWHP at 12 lbs (spring pressure), 2000 RWHP at 27 lbs of boost, and we can go to 35, just haven't put all the pieces together at the track yet.... We do spin this motor to 9000 RPM.... she starts making power at 6000 rpm....