Thread: Engine Performance Question

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  1. #1 Engine Performance Question 
    GT Level Member Hurricane87's Avatar
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    The LS4 in my GXP generally performs much better than the one in my Monte Carlo SS, with one notable exception. Giving it premium fuel produces absolutely no performance difference over regular. Any ideas as to why?
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  2. #2 Re: Engine Performance Question 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    What you feel and what is actually happening are two different things.

    If you did back to back dyno sessions with pump 87 and pump 93, the 93 octane is going to produce stronger numbers. You beat on a engine running 87 octane it will catch up to you, not that it's going to harm it more so in what the computer is going to see and do because of running lower octane fuels.

    87 octane has less resistances to knock compared to 93 octane. You flog the piss of out it on 87 and it will start to show knock as cylinder temps continue to rise. The computer can seamlessly pull timing away to keep things safe and doing so it's robbing some horsepower and torque. We aren't talking 50hp here but probably 10-20hp and that is not something you are going to notice in the butt dyno because there are so many other variables going on.

    If you want it to run at it's best with the potential to have it's most power, you'd need to run premium fuel. Or if you ask me, at least 89 octane. I've tuned many LS based V8 engines and 87 is just terrible for making good consistent horsepower with minimal to no spark knock.

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  3. #3 Re: Engine Performance Question 
    GT Level Member Hurricane87's Avatar
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    Quote Originally Posted by Fivefingerdeathpunch View Post
    What you feel and what is actually happening are two different things.

    If you did back to back dyno sessions with pump 87 and pump 93, the 93 octane is going to produce stronger numbers. You beat on a engine running 87 octane it will catch up to you, not that it's going to harm it more so in what the computer is going to see and do because of running lower octane fuels.

    87 octane has less resistances to knock compared to 93 octane. You flog the piss of out it on 87 and it will start to show knock as cylinder temps continue to rise. The computer can seamlessly pull timing away to keep things safe and doing so it's robbing some horsepower and torque. We aren't talking 50hp here but probably 10-20hp and that is not something you are going to notice in the butt dyno because there are so many other variables going on.

    If you want it to run at it's best with the potential to have it's most power, you'd need to run premium fuel. Or if you ask me, at least 89 octane. I've tuned many LS based V8 engines and 87 is just terrible for making good consistent horsepower with minimal to no spark knock.
    Unrelated question, perhaps, but you brought it up. If "you won't notice 10-20 hp," why on Earth did the previous owner do the Magnaflow catback, which couldn't possibly provide more than that?
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  4. #4 Re: Engine Performance Question 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    Probably from internet hype and the sound they wanted.

    After the cat or cat-back exhaust system don't add any real horsepower at all on an engine like this. The power gains are had before the converter with a set of headers but that's another topic.

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