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Thread: Fuel Octance

  1. #1

    Fuel Octance

    hey guys,

    Just wondering what octane you guys run in your rxp's. I have a 97 xp that i run straight 93 octane fuel in it. I was thinking about mixining in a gallon or two of cam with 14 gallons of 93? Would this be ok, more power etc.? just wondering?


  2. #2
    Moderator Snoman's Avatar
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    I run straight 93 octane right from the pump.As far as mixing..never did it so i cant help ya there sorry

  3. #3
    suck my wake's Avatar
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    Just run pump premium unless you have lots of mods,EMS system and turbo. Otherwise your just wasting money cause you will see no gains just loss's in your wallet

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    Suckmywake is right. Unless you're having detonation or retarding your timing to prevent it, you'll pick up very little with race gas. Small gains have been reported with race gas when it's not needed for detonation control, but they're on the order of 2%.

    Mike

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    Two Strokers run best on 91 octane stock.

  6. #6
    HORSEPOWER JUNKIE 9secZO6's Avatar
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    Everyone is right here, but 1 more factor....REMEMBER, when the octane rating changes, it means the fuel burns at a different rate. This is why low octane hates more timing, it burns FASTER. Higher octane burns slower and needs to be lit off sooner, but w/o changing the tune, too much octane and u will loose power. To this day I argue that FACT w/ people w/ stock camaros or whatever goin to the track filled up w/ race gas Spike it to be safe if u want, but unless u tune for the race gas, I would save the money for a 12pk

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    I hate to disagree with my fellow Louisianian-9-second-GM-late-model-performance-car-and-RXP-owner, but . . . dyno tests have proven that even low compression motors make more power with race gas. I found this article very enlightening when it came out years ago. Dyno results were:

    Hot Rod magazine, December 2001, "Octane Shootout"

    Engine: 360 Mopar at 10.4/1 compression.

    87 octane: 396.0 hp at 36 deg timing.
    91 octane: 402.1 hp at 36 deg
    100 octane unleaded: 403.5 hp at 37 deg
    114 octane leaded: 408.3 at 31 deg

    Note that the 114 required the least timing to make the most power. Their explanation was that the higher octane fuel simply burned faster due to the molecular makeup resulting from further refining.

    Mike

  8. #8
    HORSEPOWER JUNKIE 9secZO6's Avatar
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    Quote Originally Posted by engineermike View Post
    I hate to disagree with my fellow Louisianian-9-second-GM-late-model-performance-car-and-RXP-owner, but . . . dyno tests have proven that even low compression motors make more power with race gas. I found this article very enlightening when it came out years ago. Dyno results were:

    Hot Rod magazine, December 2001, "Octane Shootout"

    Engine: 360 Mopar at 10.4/1 compression.

    87 octane: 396.0 hp at 36 deg timing.
    91 octane: 402.1 hp at 36 deg
    100 octane unleaded: 403.5 hp at 37 deg
    114 octane leaded: 408.3 at 31 deg

    Note that the 114 required the least timing to make the most power. Their explanation was that the higher octane fuel simply burned faster due to the molecular makeup resulting from further refining.

    Mike
    Agreed to a point, but go to 37 deg w/ the 114 show me a number worth the money that 114 os over the 100. The fact in my mind is u need the increased compressoin to make it worth doing, unless KR is an issue. Take the 360 mopar to 13:1 comp. and then the 114 makes a lot more than 1-2% power, making it worth the money and effort. Notice the difference between the 91oct and 100 oct. numbers (+1deg and less than 2hp at the 400hp level) This is all I am trying to say. I have used 100oct to spike, but do u realize what it would cost to fill a ski w/ 114 On another note, I would like to see u sometime, do u get to Thunder Racing often?

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    Quote Originally Posted by 9secZO6 View Post
    Agreed to a point, but go to 37 deg w/ the 114 show me a number worth the money that 114 os over the 100.
    The timing was actually adjusted for max power. Yes, the 114 octane made more power at 31 deg than it did at 37, and the converse is true for the 87 octane. Totally counter-intuitive if you assume that the burn rate is slower for the higher octane, which it isn't.

    Quote Originally Posted by 9secZO6 View Post
    The fact in my mind is u need the increased compressoin to make it worth doing, unless KR is an issue. Take the 360 mopar to 13:1 comp. and then the 114 makes a lot more than 1-2% power,
    I totally agree. My Camaro is turbocharged and with race gas I can raise the boost 6 - 8 psi, resulting in 200 more hp.

    Quote Originally Posted by 9secZO6 View Post
    ...do u get to Thunder Racing often?
    Geoff is actually a friend of mine, though I haven't been over there much lately. I used to drop in about 2-3 times a month just to discuss the latest R&D efforts or get the top spot at dyno day. Ever since I reached my goal of <10 seconds with my Z28 (9.9 at 146 mph), I kinda' have been out of the car scene. Funny how that works. BTW I live about 15 minutes from Thunder.

    Mike

  10. #10
    HORSEPOWER JUNKIE 9secZO6's Avatar
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    Well Mike, I live 1 1/2 hours away, (but been there 6 times in 4 weeks ). U know, just because u hit a personal goal does not mean the game stops. If it's in u it's in u. The power we made in street cars 15 years ago would be smoked by the bank manager that just bought a modern hp car. Remember when u needed a cage to go 11.99? Now its 11.49........10.99 in 3 years..............just watch If u are that tight w/ Geoff then u know we are where the good food and strippers are Gonna try to get some parts Geoff needs this sat so I'll have him call u and we can do lunch and tip-a-stripper (don't tell his wife, either 1!)

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