Optimal Compression?
Optimal Compression? In your opinion what would be optimal compression for a forged 347ci LS1 at 12-13psi w/ a procharger? Will this engine have serious issues with stock compression, or am I going to have to go with the 6.0L heads?
How tough is 12-13psi going to be on the forged bottom end? I will probably run different pulleys for the street and run about 7psi or so of boost, but I will swap pulleys to up compression for some drag strip duty.
Thanks!
How tough is 12-13psi going to be on the forged bottom end? I will probably run different pulleys for the street and run about 7psi or so of boost, but I will swap pulleys to up compression for some drag strip duty.
Thanks!
depends on the octane fuel you are running...
if you run 100 octane then u could get away with 10.0 CR
but more then likey...u will run 91-93 octane..so i would say 9.0 - 9.5
if you run 100 octane then u could get away with 10.0 CR
but more then likey...u will run 91-93 octane..so i would say 9.0 - 9.5
TECH Senior Member
Joined: Nov 2001
Posts: 11,603
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From: Chi-Town, IL
I'm running a 9:1 setup on my motor, runs just fine N/A.....I should of gone 8:1 or 8.5:1 so I can run pump gas....
I'm shooting for 15-17psi, not sure where its going to be at yet, but I'm running 100 octane for it
I'm shooting for 15-17psi, not sure where its going to be at yet, but I'm running 100 octane for it
Originally Posted by Ralph L
In your opinion what would be optimal compression for a forged 347ci LS1 at 12-13psi w/ a procharger? Will this engine have serious issues with stock compression, or am I going to have to go with the 6.0L heads?
How tough is 12-13psi going to be on the forged bottom end? I will probably run different pulleys for the street and run about 7psi or so of boost, but I will swap pulleys to up compression for some drag strip duty.
Thanks!
How tough is 12-13psi going to be on the forged bottom end? I will probably run different pulleys for the street and run about 7psi or so of boost, but I will swap pulleys to up compression for some drag strip duty.
Thanks!
I am running 17lbs of boost, 746rwhp with an unlocked T400, so it would be like 800rwhp thru an M6.
I am running ported 6.0 heads. Mine were cut a bit so they are 69cc's, stock LS1's are 67cc's. Realistically that's not a huge difference but I wanted heads that flow around 300/225 @.600 and that's what I have.
Denz what blower car do you have experience with? How is Norm these days.
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Thank you very much for the responses, gentlemen. I will try and get the compression down as low as possible, hopefully around 9:1 compression, as I want to use 93 octane, and since this is a street car, race fuel is not an option at this point. This may be a stupid question, but is there a weight difference between the LQ9 (6.0L) truck heads, and the 5.7 heads?
Thanks again!
Thanks again!
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6.0 heads can be 70/71 cc's stock, so you can decrease compression by about .3/.4 with them over LS1 heads which are 67cc. 6.0 heads are basically LS6 heads with larger combustion chambers. -8.6cc Diamond FI pistons + 6.0 heads can be around 8.9:1 on the optimal side, my setup is around 9.1:1.
All of the aluminum heads are within an ounce of each other.
If I could do it all over again I would have gone 8.5:1 to see about doing 700rwhp on 93 pump gas.
All of the aluminum heads are within an ounce of each other.
If I could do it all over again I would have gone 8.5:1 to see about doing 700rwhp on 93 pump gas.
I'm running 9.1 to 1 on my setup.. With 11psi of boost at max rpm, I'm fine. But if I ever step up and buy the ATI F1 head unit and see 15psi of boost. I will be running better gas than the 93.5 i'm running right now. I would say 9 to 1 is fine up to 13 or 14psi with a little better octane. But if you know for a fact you will be seeing 15psi. I would go to 8.5 to 1 like PSJ stated, and be on the safer side and be able to run pump gas.
clint
clint
i run 11psi every day with my car and 93 octane, liquid intercooler with ambient temp water... can probably squeeze another psi out of it if i back the timing down from the 24.5* its at.
Thanks again, guys! I will go with the 6.0L heads, and since I'll probably be going with a forged short block, I will talk with the builder about the Diamond Pistons and hopefully can drop compression slightly below 9.0:1, maybe even get down to 8.5:1.
TECH Regular
Joined: May 2003
Posts: 404
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From: Jacksonville, FL
I believe to drop the compresson lower than 9:1 with a stock (3.9/3.905) bore you'll have to get a custom set of pistons made.
Anyone know of an off the shelf piston that will lower the compression to 8.5:1 or lower with 71cc heads?
Anyone know of an off the shelf piston that will lower the compression to 8.5:1 or lower with 71cc heads?
