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Old 11-17-2009, 07:33 PM   #1
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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
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Old 11-17-2009, 07:59 PM   #2
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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.
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Old 11-17-2009, 11:17 PM   #3
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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.
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Old 11-18-2009, 12:10 AM   #4
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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.
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Old 11-18-2009, 02:01 PM   #5
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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??
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Old 11-18-2009, 02:52 PM   #6
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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.
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Old 11-18-2009, 02:52 PM
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