compression ratios
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
compression ratios
on a fresh/rebuilt motor, what are the octane approximations versus compression ratio? Let's assume a mild cam (no serious overlap) and aluminum heads- iron heads demand about a point less right?
I'm specifically looking for 89 & 91 octane recommendations; will 10:1 avoid detonation?
I'm specifically looking for 89 & 91 octane recommendations; will 10:1 avoid detonation?
Drifting
Joined: Mar 2001
Posts: 1,351
Likes: 1
From: Kingwood TX
Re: compression ratios (Ramanstud)
If I remember correctly my '91 which is a TPI L98 has a 10.25:1 compression ratio. If you always run premium you could easily bump that .25 to 10.5 and not have a problem. But since you are looking at 89 or 91 octane I guess stay at 10 like you suggested. On my car even if compression was a little lower I would not go with 89 octane but thats just me...
Instructor
Joined: Dec 2001
Posts: 147
Likes: 0
From: Riverside CA
Re: compression ratios (Ramanstud)
Just go with the 91 octane and, if you don't have detonation try the 89. But remember, not all 91 is the same, even from batch to batch. It's like using syn oil, only the best will do... But stay below 10.1 at all costs. :)
[Modified by myblack864+3, 6:20 AM 10/23/2002]
[Modified by myblack864+3, 6:20 AM 10/23/2002]
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
Re: compression ratios (Ramanstud)
thanks for the advice, guys. It's my daily and I'd like to save a few pennies at the pump! And God know's what 91 will run once we give up on the beurocratic BS and get some sand in our combat boots.
:flag:
:flag:
Melting Slicks
Joined: Apr 2002
Posts: 3,019
Likes: 0
From: down that one road next to that big tree
Re: compression ratios (Ramanstud)
mild cams are worse than aggressive cams, low duration cams build cylinder pressure early. i can run the engine on my sig on 92 quite well, seems to do really good with just a cheap $3 can of octane booster. if i only ran pump gas i would have went more around 10:5-1. the higher duration cams and low deck height also promote high compression with pump gas
Team Owner
Joined: Apr 2001
Posts: 22,267
Likes: 3
From: Dallas TX
Re: compression ratios (gtsyellow)
my 11.5:1 needed about 95 octane, stock LT4 which is 10.8:1 says it needs 91 minimum. (for reference) So i'd say with 10:1 you could get away with about 90 or so. Depends on a LOT of variables though! :yesnod:
Instructor
Joined: Dec 2001
Posts: 147
Likes: 0
From: Riverside CA
Re: compression ratios (Ramanstud)
Sorry to reply again
But if we could turn the clock back to when Oldsmobile built lots of engines with 10.5 compression, you could buy Chevron Custom Supreme for $.42 a gallon and it was 101 octane at the pump, tetraeythel lead included!
But if we could turn the clock back to when Oldsmobile built lots of engines with 10.5 compression, you could buy Chevron Custom Supreme for $.42 a gallon and it was 101 octane at the pump, tetraeythel lead included!
Team Owner
Joined: Sep 2001
Posts: 62,182
Likes: 1,740
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: compression ratios (myblack864+3)
There are alot of other things to think about, but its good to keep compression below 10.5:1 to run pump gas
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Le Mans Master
Joined: Feb 1999
Posts: 9,959
Likes: 40
From: South Carolina
St. Jude Donor '03 & '05
Re: compression ratios (GlockLT4)
Think about this, they run Superchargers on cars with LT-1/4 compression ratios. I have a 396 with about 10.6 to 1, and I could very easily run a supercharger, HMM ATI, VOrtech, HP gain. Will my bank allow this. Be right back.. :yesnod:
Le Mans Master
Joined: Feb 1999
Posts: 9,959
Likes: 40
From: South Carolina
St. Jude Donor '03 & '05
Re: compression ratios (GlockLT4)
Think about this, they run Superchargers on cars with LT-1/4 compression ratios. SO 11.0 to 1 is reasonable. It all in the tuning too. I have a 396 with about 10.6 to 1, and I could very easily run a supercharger, HMM ATI, VOrtech, HP gain. Will my bank allow this. Be right back.. :yesnod:
Racer
Joined: Aug 2002
Posts: 432
Likes: 0
From: Lancaster CA
Re: compression ratios (steve40th)
keep in mind that part of the reason that LTx engines can run such high comp ratios is due to their reverse flow cooling keeping those heads nice and cool. (reducing detonation)