Optimal FI compression ratio
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 5,786
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From: Lafayette Colorado
Optimal FI compression ratio
What you be a good optimal for a S/C application? I am planning on runing a 408 LQ4 block with with -15cc pistons and LQ4 heads with 75cc chambers. This should give a static compression ratio of 9.3:1. With this compression ratio and having the stroker, would it still give somewhat 'ok' performance under non boost conditions, aka low rpms? Lastly, would this be able to run about 13 psi of boost using ARP head studs?
Keith
Keith
Drifting
Joined: Oct 2002
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From: If you can see the car behind you, your not going fast enough
Re: Optimal FI compression ratio (kromberg)
ok... i am pretty good w/ car stuff but DAMN! I could barely undersatnd what you typed:crazy: ... Try and contact Chris at ECS or andy at A&A
Melting Slicks
Joined: Apr 2002
Posts: 3,159
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From: Hail 2 Da Victorz!
Re: Optimal FI compression ratio (kromberg)
I would say a C.R. of about 9:1 would work out pretty good, you don't want to go too low because your off-boost performance will be sluggish, your 9.3:1 should work great and give you solid off-boost performance. :yesnod:
Melting Slicks
Joined: Jun 2002
Posts: 3,060
Likes: 3
From: Dublin CA
Re: Optimal FI compression ratio (kromberg)
Andy typically builds 9.8:1 with a -2cc piston dish. He pointed me to an online compression calculation tool at http://www.Rosspistons.com.
Stock motor is 3.905" bore & 3.622" stroke. Head chamber (A&A S2 CNC heads) is 71cc, I'm not sure what stock is. Gasket thickness is .050" but type in .040" since the piston sticks up .010". Zero deck on the calculator is .0001. My pistons have a -8.6cc dish. For me this works out by hand to 8.9:1, but the online calculator has me at 9.1:1
Stock motor is 3.905" bore & 3.622" stroke. Head chamber (A&A S2 CNC heads) is 71cc, I'm not sure what stock is. Gasket thickness is .050" but type in .040" since the piston sticks up .010". Zero deck on the calculator is .0001. My pistons have a -8.6cc dish. For me this works out by hand to 8.9:1, but the online calculator has me at 9.1:1
Le Mans Master
Joined: Apr 2000
Posts: 7,248
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Re: Optimal FI compression ratio (blu00rdstr)
Better calculator here: http://www.csgnetwork.com/compcalc.html
Watch gasket compressed thickness and pistons, in/out of the hole above deck. Also gasket bore.
.010 out of the hole will give you good quench, but may be dangerous depending on the compressed gasket thickness. Also if you ever have to deck the block in the future, the pistons will be too high.
My current 9.5:1 setup:
3.910 (honed)
3.62
.051 Cometic (compressed thickness)
3.925 Gasket Bore
66.5cc Stock LS1 Heads
-8cc dished
-.005 (out of the hole)
Watch gasket compressed thickness and pistons, in/out of the hole above deck. Also gasket bore.
.010 out of the hole will give you good quench, but may be dangerous depending on the compressed gasket thickness. Also if you ever have to deck the block in the future, the pistons will be too high.
My current 9.5:1 setup:
3.910 (honed)
3.62
.051 Cometic (compressed thickness)
3.925 Gasket Bore
66.5cc Stock LS1 Heads
-8cc dished
-.005 (out of the hole)
