Higher Compression Ratios= More HP?
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Originally Posted by bobmic93
What do you guys think? Any HP gains by going with the Cometic? How does higher compression change the characteristics of the car?
11.3 is fine on pump gas with an LT1.
Personally I wouldn't shave the heads for compression.
Thread Starter
Melting Slicks
Joined: Jul 2004
Posts: 2,695
Likes: 0
From: Chicago Illinois
Static/dynamic compression, quench space are all things Im not up to par on and I will have to rely on my porter( Phil from Advanced Induction and my installer from LS1 Speed INC. ) Both have good reputations in the industry. But on this issue there on different pages. I have confidence in Phil(porter) knowledge on the topic butt my decesion will be 90% influenced from you guys. My time is running out. Which ratio would you shoot for? 50,000 miles and I always run 93 octane with 160 stat. Thanks fellas 
Race Director
Joined: Feb 2004
Posts: 12,517
Likes: 19
I am going to go against the grain and say"don't do it". You are talking 1/2 point of compression.
"If" a full point is worth a true 3%. We are talking about 6 horse power, assuming a 400 hp motor. Even if we are talking 500 horses, 7 1/2 hp possibility does not seem, to me, worth the possible problems. .
"If" a full point is worth a true 3%. We are talking about 6 horse power, assuming a 400 hp motor. Even if we are talking 500 horses, 7 1/2 hp possibility does not seem, to me, worth the possible problems. .
Burning Brakes
Joined: Jun 2003
Posts: 937
Likes: 0
From: Bedford Tx
after thinking about this for awhile,
it is not clear to me that high compression
is even desireable.
consider this thought experiment...
the same fuel is used, say pump93, or whatever
smog is not an issue
spark advance can be set as needed
....................
Case 1, goal is max power at WOT at some high, but reasonable RPM.
Case 2, goal is improved efficiency at part throttle,
some loss of max WOT power is acceptable
......................
I would think this might be possible,
going from case 1 to case 2, the engine designer
would increase the CR, to get more efficiency at part throttle, then at WOT, being forrced to back off
of the spark advance to get knock under control,
resulting in less WOT power than in case 1.
............................
meaning, possibly, if something came from the factory,
optimised for part throtle efficiency, you
would not even want higher CR.
would anyone like to comment?
it is not clear to me that high compression
is even desireable.
consider this thought experiment...
the same fuel is used, say pump93, or whatever
smog is not an issue
spark advance can be set as needed
....................
Case 1, goal is max power at WOT at some high, but reasonable RPM.
Case 2, goal is improved efficiency at part throttle,
some loss of max WOT power is acceptable
......................
I would think this might be possible,
going from case 1 to case 2, the engine designer
would increase the CR, to get more efficiency at part throttle, then at WOT, being forrced to back off
of the spark advance to get knock under control,
resulting in less WOT power than in case 1.
............................
meaning, possibly, if something came from the factory,
optimised for part throtle efficiency, you
would not even want higher CR.
would anyone like to comment?
Safety Car
Joined: Dec 2004
Posts: 4,088
Likes: 0
From: Poop land
I know that I put 87 octane gas when I went to race on the 1/8th mile dragstrip. I ran an 8.8 @ 84 mph. The next time I went to the strip, I used 93 octane gas and I ran a 9.1 @ 82 mph. That is on the stock timing of 6 degrees BTDC, same chip that Alvin burnt me. Strange how higher octane gas made my car run slower. When I did a WOT scan, I noticed only 3 knock counts on 87 octane gas and 2 knock counts on 93 octane premium gas.
What would make my car perform better with 87 octane?
What would make my car perform better with 87 octane?
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Race Director
Joined: Feb 2004
Posts: 12,517
Likes: 19
Originally Posted by kopbet89c4
I know that I put 87 octane gas when I went to race on the 1/8th mile dragstrip. I ran an 8.8 @ 84 mph. The next time I went to the strip, I used 93 octane gas and I ran a 9.1 @ 82 mph. That is on the stock timing of 6 degrees BTDC, same chip that Alvin burnt me. Strange how higher octane gas made my car run slower. When I did a WOT scan, I noticed only 3 knock counts on 87 octane gas and 2 knock counts on 93 octane premium gas.
What would make my car perform better with 87 octane?
What would make my car perform better with 87 octane?
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
You folks are putting far too much thought into this...compression is free horsepower...not running as much as possible (for the gas) is like leaving HP on the table.
Read any high performance book/magazine and this is one of the basics. Why reinvent the wheel???
Why would 87 run better than 93 octane...probably because the air was not as good or the launch was not as good or your trans is going south or countless other items. Two runs do not make a good 'sample.'
Read any high performance book/magazine and this is one of the basics. Why reinvent the wheel???
Why would 87 run better than 93 octane...probably because the air was not as good or the launch was not as good or your trans is going south or countless other items. Two runs do not make a good 'sample.'
Safety Car
Joined: Dec 2004
Posts: 4,088
Likes: 0
From: Poop land
Originally Posted by No Go
You folks are putting far too much thought into this...compression is free horsepower...not running as much as possible (for the gas) is like leaving HP on the table.
Read any high performance book/magazine and this is one of the basics. Why reinvent the wheel???
Why would 87 run better than 93 octane...probably because the air was not as good or the launch was not as good or your trans is going south or countless other items. Two runs do not make a good 'sample.'
Read any high performance book/magazine and this is one of the basics. Why reinvent the wheel???
Why would 87 run better than 93 octane...probably because the air was not as good or the launch was not as good or your trans is going south or countless other items. Two runs do not make a good 'sample.'
