Find my CR please!
Thread Starter
TECH Regular
Joined: Jul 2006
Posts: 452
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From: Sacramento, CA
Find my CR please! 
Im trying to keep the CR below 11.5:1
355, .030 over, 5.7 rods, pistons are flat tops with 4cc valve reliefs,
http://www.summitracing.com/parts/PBP-12334-030/
^^ link to the pistons
Heads are LE ported w/ 55cc chambers..
Heres where the confusion sets in. Machine shop says that stock head gasket .051 will yield ~11.1 CR and probe says a .039 HG will get ~11.1 CR.
My main concern is detonation in CA with 91 octane and HOT summers.
Preventative measures being taken are 160 thermostat and NGK TR6 plugs gapped at .045.
I really need help deciding on what size HG to get 11:1-11.4:1 CR I really can't afford to F this up.
1) Your concerns are unfounded.
2) Your machinist is full of ****
3) If you cant figure this out you shouldnt be working on your own ****
4) Its impossible to accurately find your compression ratio because we need to know deck height
5) Dont really know which head gasket spec you're asking someone to find the CR with, but here are a few guesses just for fun, and assuming your block has not been decked....
Assuming the block does not get decked:
.051 head gasket = 10.58 : 1
.041 head gasket = 10.85 : 1
2) Your machinist is full of ****
3) If you cant figure this out you shouldnt be working on your own ****
4) Its impossible to accurately find your compression ratio because we need to know deck height
5) Dont really know which head gasket spec you're asking someone to find the CR with, but here are a few guesses just for fun, and assuming your block has not been decked....
Assuming the block does not get decked:
.051 head gasket = 10.58 : 1
.041 head gasket = 10.85 : 1
Thread Starter
TECH Regular
Joined: Jul 2006
Posts: 452
Likes: 0
From: Sacramento, CA
Just my opinon man. Take it or leave it.
Now for the real questions:
Are you having the block decked?
Who is assembling the engine?
Why on earth do you think you will have detonation issues if you dont keep the CR below 11.5:1 ?
Is this an N/A project or will it ever see nitrous, and if so how much?
Is your machinist familiar with LT1's?
Now for the real questions:
Are you having the block decked?
Who is assembling the engine?
Why on earth do you think you will have detonation issues if you dont keep the CR below 11.5:1 ?
Is this an N/A project or will it ever see nitrous, and if so how much?
Is your machinist familiar with LT1's?
Thread Starter
TECH Regular
Joined: Jul 2006
Posts: 452
Likes: 0
From: Sacramento, CA
short block is already assembled. Unfortunately deck clearance was not checked before i picked it up. ( I am pissed about this) However, deck height came out to be ~9.011 and stock is ~9.025 if I am not mistaken. I am assembling the top end and a few more pieces on the bottom end. Nitrous is an option but is not a priority.
Put a .026 or .028 or whatever the impala gasket is on it. What are the cam specs? You're stuck with whatever compression the pistons and heads give you, now run the thinnest head gasket you can to promote even combustion. You're hit or miss spraying on CA crap gas, so don't bother.
short block is already assembled. Unfortunately deck clearance was not checked before i picked it up. ( I am pissed about this) However, deck height came out to be ~9.011 and stock is ~9.025 if I am not mistaken. I am assembling the top end and a few more pieces on the bottom end. Nitrous is an option but is not a priority.
at that point your piston is .011 down the hole at TDC.....if you run a run of the mill felpro at .039 compressed your compression will be at 11.4.........which IMO is perfect for what you are doing...........your quench will be a bit large at .050 but its not the end of the world for your application...........hope this helps!!
fyi also.....if you do plan on spraying the car I'd reccomend a MLS gasket such as a cometic.......and dumping a couple of gallons of race gas in with that 91 would give you some added detonation suppression over the CA gas for when ur using the baby bottle
good luck!!
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Thread Starter
TECH Regular
Joined: Jul 2006
Posts: 452
Likes: 0
From: Sacramento, CA
IF that is your deck height it sounds like you got about .014 chopped off the deck......usually a 9" deck will put the piston at 0.....depending on compression height of course.......but im making that assumption based off of a standard compression hieight.....
at that point your piston is .011 down the hole at TDC.....if you run a run of the mill felpro at .039 compressed your compression will be at 11.4.........which IMO is perfect for what you are doing...........your quench will be a bit large at .050 but its not the end of the world for your application...........hope this helps!!
fyi also.....if you do plan on spraying the car I'd reccomend a MLS gasket such as a cometic.......and dumping a couple of gallons of race gas in with that 91 would give you some added detonation suppression over the CA gas for when ur using the baby bottle
good luck!!
at that point your piston is .011 down the hole at TDC.....if you run a run of the mill felpro at .039 compressed your compression will be at 11.4.........which IMO is perfect for what you are doing...........your quench will be a bit large at .050 but its not the end of the world for your application...........hope this helps!!
fyi also.....if you do plan on spraying the car I'd reccomend a MLS gasket such as a cometic.......and dumping a couple of gallons of race gas in with that 91 would give you some added detonation suppression over the CA gas for when ur using the baby bottle
good luck!!
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