Compression Ratio and Forced Induction - Pontiac G8 Forum: G8 Forums - G8Board.com
 
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post #1 of 6 (permalink) Old 05-18-2017, 08:28 PM Thread Starter
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Compression Ratio and Forced Induction

Today I was laying out a plan for turbocharging my G8 V6. Finding the right parts and installing the turbo system does not seem like that difficult a process, but I have a question that could make or break my plans.

With a stock compression ratio of 10.2:1, how is it possible to run any amount of boost without having to run with racing gas or higher? I know some people that run 6 to 9 psi on C.A.P.A Raptor Superchargers and can still run on pump 91/93 octane. From my calculations though, running that much boost would shoot the compression ratio far above a "safe" 12.0:1. (About the max for pump gas, so I have heard). Anyways, there is no way I am going to buy lower compression ratio pistons for the V6 just to turbocharge.

How is it possible to run 6-9 psi of boost on the V6 Alloytec without blowing the engine immediately? I know tuning is necessary and will help with preventing knock but even with a tune if your compression ratio is to high it wont matter anyways.

I have everything else pertaining to this subject basically understood but I can not wrap my mind around this one.

Godspeed my friends.

Current Upgrades In Order Of Installation:
12mm Intake Manifold Insulators (MACE)
K&N, Cold Air Intake
20% Underdrive Power Pulley Kit. (Powerbond from MACE)
Possible Future Upgrades. (Suggestions Welcome):
Ported Stock Exhaust Manifolds. 76mm Throttle Body. Ported Intake Manifold. Tune.
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post #2 of 6 (permalink) Old 05-18-2017, 09:17 PM
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Les on the board may be able to help you, the only other people would be the Aussies on here, pir4te or Nick Ash. Haven't heard much from Nick lately but pir4te is extremely knowledgable about these cars and engines.
From the peanut gallery, I'd lean more towards a supercharger than turbo, but there both so far out of my league to worry about.
Good luck, your build will be interesting.
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post #3 of 6 (permalink) Old 05-18-2017, 09:37 PM
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I run 10.3:1 on a forged LS3, with E85, meth and mild timing. Not knowing anything about the internals of a stock V6, I assume they're garbage. It would probably be easier and cheaper to swap a junkyard 5.3 and turbocharge that than to make decent, reliable power on the V6.
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post #4 of 6 (permalink) Old 05-18-2017, 10:23 PM Thread Starter
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The only reason I was leaning towards a turbo is because of cost. A supercharger kit would be easier to install but it seems to be way more expensive.

Current Upgrades In Order Of Installation:
12mm Intake Manifold Insulators (MACE)
K&N, Cold Air Intake
20% Underdrive Power Pulley Kit. (Powerbond from MACE)
Possible Future Upgrades. (Suggestions Welcome):
Ported Stock Exhaust Manifolds. 76mm Throttle Body. Ported Intake Manifold. Tune.
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post #5 of 6 (permalink) Old 05-18-2017, 10:31 PM Thread Starter
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Quote:
Originally Posted by MGMGXP View Post
I run 10.3:1 on a forged LS3, with E85, meth and mild timing. Not knowing anything about the internals of a stock V6, I assume they're garbage. It would probably be easier and cheaper to swap a junkyard 5.3 and turbocharge that than to make decent, reliable power on the V6.
I am not very familiar with E85 gas. Its sort of a cheap alternative to race gas that is a mix between ethanol and gas? Also, with the compression ratio you are running why is it necessary to run E85? Couldn't you stick to standard pump gas and be ok? Maybe I have this completely wrong, but from what I have researched if I boost my 10.2:1 LY7 V6 engine even with 3 to 4 psi, the compresssion ratio will be so high that I would have to run on nothing but race (or maybe E85) gas.

Anyways, thanks for the replies, I really needed some personal experience input. Keep the info coming if you have anything else for me.

Current Upgrades In Order Of Installation:
12mm Intake Manifold Insulators (MACE)
K&N, Cold Air Intake
20% Underdrive Power Pulley Kit. (Powerbond from MACE)
Possible Future Upgrades. (Suggestions Welcome):
Ported Stock Exhaust Manifolds. 76mm Throttle Body. Ported Intake Manifold. Tune.
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post #6 of 6 (permalink) Old 05-19-2017, 04:45 AM
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If you're boosted, e85 is your friend.

things are not as they appear to be.........

2009.5 LiquidRed/OnyxRed, Premium Package
e85 Surprise Package
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