9.5:1 Compression ratio???? - Third Generation F-Body Message Boards

Tech / General Engine Is your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!

9.5:1 Compression ratio????

Thread Tools Search this Thread
Old 11-17-2009, 07:33 PM   #1
Thread Starter
servo2055chevy's Avatar
Join Date: Feb 2009
Location: New Jersey
Posts: 305
Car: 1988 Camaro Base model
Engine: 305 LO3 5.0L V8 TBI
Transmission: 700R4
Axle/Gears: 10Bolt Rear, Not sure the gearing

9.5:1 Compression ratio????

I have th 83 Camaro CFI That has the cam from a 350 and gives it a 9.5:1 Compression ratio and i heard it runs best on 92-94 Octane. Is that true, and where can i get 94 octane at, its not pump gas, and would 95 octane from vpracefuel be fine in the engine. It is stock except for an exhaust and the airfilters but the 305CFI in '83 came with the 350 L69 Cam or something giving it a "high performance" 9.5:1 Compression ratio as they said. Please Let me know, I know that i can run reg 93 pump gas but I want to just see how much better it does on 94 or 95 if y'all think it is safe
servo2055chevy is offline vBGarage Page   Reply With Quote
Old 11-17-2009, 07:59 PM   #2
Supreme Member
iTrader: (5)
one92rs's Avatar
Join Date: Jan 2009
Location: league city
Posts: 2,928
Car: SOLD!!!!!

Re: 9.5:1 Compression ratio????

i thought it was cylinder volume that gave an engine compression. not the cam. although the wrong cam can bleed off compression. most cars today run 9-5-1 compression and they can run on 87 octane. 94 not sure on that. i know there is 93 here in texas. i run it all the time.
one92rs is offline vBGarage Page   Reply With Quote
Old 11-17-2009, 11:17 PM   #3
Join Date: May 2009
Location: Marseilles, IL
Posts: 117
Car: 91 RS, 89 IROC
Engine: 305 TBI, still deciding
Transmission: 700R-4, still deciding
Axle/Gears: stock, 3:73 IROC

Re: 9.5:1 Compression ratio????

You wont notice a difference from 93 octane to 94 or 95. You won't hurt anything either except your wallet. Only need to run high enough octane to stay out of detonation.
DJ_91RS is offline vBGarage Page   Reply With Quote
Old 11-18-2009, 12:10 AM   #4
Supreme Member
Join Date: Jan 2009
Location: belle fourche,s.d.
Posts: 1,679
Car: '82 z28
Engine: L83 5.7
Transmission: 700r4-1985
Axle/Gears: 3.42 posi

Re: 9.5:1 Compression ratio????

it is the heads and pistons that determines the C/R
The CFI engines have electronic spark control with a
knock sensor-if pinging is detected the ECM will pull
back the timing advance,reducing power until no more
pinging or"knock"is detected. the L69 carbed engine
also had electronic spark control and GM rated that
engine at 190HP,200HP if high octane gas used.
8t2 z-chev is offline vBGarage Page   Reply With Quote
Old 11-18-2009, 02:01 PM   #5
Supreme Member
iTrader: (1)
Sonix's Avatar
Join Date: Jul 2004
Location: Calgary, AB, Canada
Posts: 10,763
Car: 1982 Trans-Am
Engine: 355 w/ ported 416s
Transmission: T10, hurst shifter
Axle/Gears: 10 bolt, true-trac, 3.73

Re: 9.5:1 Compression ratio????

Depends on your gas stations. Mohawk sells 94 octane at the pump here in Calgary.

9.5:1 CR does NOT need any more then 87-89 octane. I doubt you have more than 9.5:1 CR anyway, and yes, a cam does not determine CR, the heads and pistons and crankshaft do.

What on earth engine do you actually have??
Sonix is offline vBGarage Page   Reply With Quote
Old 11-18-2009, 02:52 PM   #6
iTrader: (14)
five7kid's Avatar
Join Date: Mar 2000
Location: Littleton, CO USA
Posts: 43,036
Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89

A cam, in combination with the cylinder and combustion chamber volumes, affects the dynamic compression ratio. But, 9.5:1 is the static compression ratio.

FWIW, I'm running 9.7:1 on 85 octane (high altitude regular unleaded). At the track, it does slightly better on 87 octane.
five7kid is offline vBGarage Page   Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Using GM drac instead of SGI-5 box? InfernalVortex Electronics 9 12-22-2016 12:56 PM
Was I too Optimistic ? TPI L98 Power FormulasOnly TPI 54 02-07-2016 05:01 PM
Diff sugestions Vincent135 Transmissions and Drivetrain 9 09-28-2015 10:50 PM
Running stock small cap CC-HEI as a cheap "locked timing" distributor? Damon Tech / General Engine 8 09-26-2015 04:29 PM
Where To Get A Factory Style Close Ratio Steering Box? 83 Crossfire TA Suspension and Chassis 0 09-08-2015 12:06 PM

Go Back   Third Generation F-Body Message Boards >

350, 355, 95, 951, cam, compress, compression, engine, gas, octane, premium, pump, ratio, recommended, run

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 09:33 PM.

All content copyright 1997 - 2014 ThirdGen.org. All rights reserved. No part of this website may be reproduced without the expressed, documented, and written consent of ThirdGen.org's Administrators.
  • Ask a Question
    Get answers from community experts
What's your question?