Boost vs compression ratio
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Re: Boost vs compression ratio (Phil97SVT)
I miscalculated my CR (used the wrong Head Volume for LS6 Heads) when I setup my last motor. I ran -7.77 cc Ross Pistons with stock LS6 Heads. My compression ratio was 10.2 instead of 9.8. I was running 13-15lbs of boost. When I took the procharger off and disassembled the motor..1200 miles the pistons looked brand new and were inspected by the engine assembler. No damage to anything on a forged motor running that much boost..However I would not intentially do it that way. I think 9.5:1-9.8:1 for a ProCharger pushing 12-15lbs and 9.1-9.5 CR for LS1 Turbo Applications and forged internals of course. My new motor came in at 9.66:1. Had a little more deck height than stock.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Re: Boost vs compression ratio (Shinobi'sZ)
I miscalculated my CR (used the wrong Head Volume for LS6 Heads) when I setup my last motor. I ran -7.77 cc Ross Pistons with stock LS6 Heads. My compression ratio was 10.2 instead of 9.8. I was running 13-15lbs of boost. When I took the procharger off and disassembled the motor..1200 miles the pistons looked brand new and were inspected by the engine assembler. No damage to anything on a forged motor running that much boost..However I would not intentially do it that way. I think 9.5:1-9.8:1 for a ProCharger pushing 12-15lbs and 9.1-9.5 CR for LS1 Turbo Applications and forged internals of course. My new motor came in at 9.66:1. Had a little more deck height than stock.
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Re: Boost vs compression ratio (SpinMonster)
Why is the higher compression bad for the set-up if there is no motor damage. Wouldn't it simply give you more power down low? I don't really understand the reason for lower compression if 10.5 can work.
I will say the biggest problem of high compression ratio and forced induction is detonation.
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Drifting
Joined: Feb 2002
Posts: 1,314
Likes: 2
From: san diego ca
Re: Boost vs compression ratio (OCMike)
The Viper Jeff????? :smash: :smash: :smash:
So I see you have your eye on the C6 ..VERY NICE :thumbs:
:cheers:
Jeff
Le Mans Master
Joined: Mar 2002
Posts: 7,179
Likes: 1
From: Honolulu Hawaii
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
Re: Boost vs compression ratio (BLUTHUNDER)
YES!...because Andy told me he already has the Turbo Kit for the C6 all figured out.... :crazy: :crazy:
Safety Car
Joined: Mar 2002
Posts: 3,556
Likes: 2
Re: Boost vs compression ratio (OCMike)
I had this very same question for FI in the future.
I've been told that high compression like mine at 11.2-1 with even 5lbs of magnacharger boost would create too much heat, negating a good chunk of power even with an octane adder. This also takes into account stressing the engine internals.
Even with an intercooler, it would not be worth it at 11.2.
I however, am far from an expert.
I feel if I keep my coolant temp below 195 degrees, and run an octane adder giving me a real 96 octane-don't think I'll experience detonation and my engine should live with 5lbs of non intercooled boost.
Everyone tells me no though :nono:
I've been told that high compression like mine at 11.2-1 with even 5lbs of magnacharger boost would create too much heat, negating a good chunk of power even with an octane adder. This also takes into account stressing the engine internals.
Even with an intercooler, it would not be worth it at 11.2.
I however, am far from an expert.
I feel if I keep my coolant temp below 195 degrees, and run an octane adder giving me a real 96 octane-don't think I'll experience detonation and my engine should live with 5lbs of non intercooled boost.
Everyone tells me no though :nono:
Pro
Joined: Aug 2002
Posts: 570
Likes: 1
From: Las Colinas, Texas
Re: Boost vs compression ratio (SpinMonster)
Why is the higher compression bad for the set-up if there is no motor damage. Wouldn't it simply give you more power down low? I don't really understand the reason for lower compression if 10.5 can work.[/QUOTE]
SpinMonster- Another way to look at it is: how many particles of fuel/air can you compress into a combustion chamber of, say 80cc's as opposed to 60cc's? The more fuel and air the more bang. ALSO The longer the fuel/air charge will continue to burn during the power stroke the greater the push on the crank. The HIGHER CR motor is spent early in the power stroke with a smaller fuel/air charge while the LOWERED CR motor is still burning and pushing well beyond. It is really simple when you think about it. Also another enemy is spark/knock retard and anything done to prevent or delay it will help power. Hence lowered C.R. Maybe not the perfect primer but others may post additional ways to look at the F.I. advantage. Hope this helps a little and good luck.
Pro
Joined: Jun 2002
Posts: 501
Likes: 82
From: Woodland Hills CA
Re: Boost vs compression ratio (BLUTHUNDER)
10.6:1 running 12PSI
Car runs awesome ! Haven't burnt a drop of oil since Andy rebuilt my internals :cheers:
Car runs awesome ! Haven't burnt a drop of oil since Andy rebuilt my internals :cheers:
Anxious to see that Snake!
[Modified by AWSM_06, 5:36 PM 12/1/2003]
Melting Slicks
Joined: Oct 2002
Posts: 2,855
Likes: 0
Re: Boost vs compression ratio (AWSM_06)
I think stock ls1 is 10.2, I've run 6lbs on 10.7 to 10.8 with no probs, I don't know how long the pistons would last if I had the chance to run it hard more often, I would rather be at 9.6 with 12 lbs, if the new systems work who knows maybe 6 or 7 lbs on the 436, it will be at 11.15cr but very strong forged motor and not sure how much boost I can get to it, maybe the F1 blower would maintain 6 or 7 I think Andy is going to be running at least that on his 409ci--BTW past 6000rpm the ATI spools up and by 6800 you will be over 8lbs, with my CR and stock bottom we set the rev at 6000 to keep the boost down, however it was a trip to see over 600rwhp at least once on the dyno, this was one of the first ATI package and it scared the s$%^ out of us when it spooled up as we had no idea what to expect--Less than a year earlier I hydo'd a new H/C motor in a deep puddle in a sudden downpour and did not want to go through another short block--
