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Race gas, should I run it?

Discussion in 'The Garage' started by sled_dog, Feb 2, 2004.

  1. sled_dog

    sled_dog 1 ton status

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    Ok I am thinking about redoing my motor in my K5. Mainly just swapping out pistons, some 64 chambered heads and bump my compression up a good bit. Say 10.5:1. Is it so uncommon for tral rig to run on race fuel? I'm looking for more power from the motor, want to be able to through a little nitrous at it as well. And race fuel smells good. My dad runs race fuel in his Street Stock class dirt track car so I have access to fuel. Only thing I can think is I would have to load the trailer with extra fuel in case we decide to take a longer run.
     
  2. vince13

    vince13 1/2 ton status

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    Well first off if you are planning on running race gas you will definatly need to do more than just pistons, you will need a good set of high quality rings, and if you are plannin on running nitrous on top of that you will definatly want to get some better than stock rods for it too. but as for running it on race gas, i think you might find it gets a little expensive being as up here in canda its 500 bucks a barrel, and that doesnt go very far. id say if your lookin for more power you are better off saving the money you would spend on race fuel and get yourself a big lumpy roller cam setup, and a nice intake and carb and that should give you some nice reliable power that will last a long time. But thats just my 2 cents.
     
  3. 99firehawk

    99firehawk 1/2 ton status

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    The trick to big compresion and pump gas. Aluminum heads are a good idea, but not necesscary. Less timing and cam selection. You want a cam that will bleed off some compression. By increasing duration for a given LSA, the overlap will increase, the intake closing will be delayed, and the exhaust opening will occur earlier. This will decrease cylinder pressure. Making pump gas run fine /forums/images/graemlins/thumb.gif
    I ran around a long time with a 350 with milled 64 cc heads and 11:1 compression on good old 92 octane.
     
  4. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Why the heck would you want to run race gas in an offroad truggy? /forums/images/graemlins/dunno.gif It is obviously not a mud runner so serious top end HP isn't necessarely needed. You would be money ahead in the long run if you just bought a blower and keep the motor timed and jetted for 89 or 91 octane then spending $500 for a barrel of race fuel. 5 barrels and the blower is free. $500x5 is 2,500. 6-71 weind...$2K...275 gallons of 91 octane....around $400 to $500 bucks.

    You aren't going to make all that much more power with 10.5:1 and race fuel than you would with say 9.5:1 on 91 octane. You would make WAY more power with the free blower and a properly set up block. /forums/images/graemlins/waytogo.gif
     
  5. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    I ran a 50%50% mixture of 105 racing fuel and 92 octane for when I did the truck pulls.. You can feel a little diffrence in it.. But at $6.25 a gallon it wasn't worth it... /forums/images/graemlins/peace.gif
     
  6. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    I'd say stick to around 9.5:1 and 91 ocatane for driving it.. When you want to add your 100 shot then mix in the race gas. I think much over 100 shot you'll want a colder spark plug and higher octane..
    My camaro is 11:1 and it pings on 91 octane.. I mix in 114 leaded @ almost $5.00 a gallon. ~4 MPG outta my big block it starts adding up quick.
    I'd avoid having to run race gas if you can.. If your gonna run race fuel anyways, might as well go all the way and build it like 15:1 compression. /forums/images/graemlins/peace.gif /forums/images/graemlins/waytogo.gif
    I'd be sure you install a fuel pressure safety cutout switch and a good fuel pump that can flow more than enough, so your engine will live a long happy life when your sqeezing on it.
     
  7. ntsqd

    ntsqd 1/2 ton status

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    [ QUOTE ]
    Ok I am thinking about redoing my motor in my K5.....Is it so uncommon for tral rig to run on race fuel? .... And race fuel smells good. ....

    [/ QUOTE ]

    Think about what octane is. It is a rating of the fuel's ability to resist detonation. It does that by being harder to ignite. By being harder to ignite it will have a slower flame front travel rate, it burns slower. So now we're using a fuel that is harder to ignite and burns at a slower rate in an engine that has been built to produce more torque at a higher RPM (HP) than stock. Am I the only one who sees the irony in this ?

    FWIW, Within a fairly narrow range all gasoline fuels have the same energy content (alcohol blends have their own range). Changing the octane of the fuel does NOT significantly increase or decrease the amount of energy in the fuel. What does happen is that a particular engine combination can extract more energy from a certain burn rate of fuel. With rare exceptions you want to run the lowest Octane fuel that the engine will run on w/o detonating.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    But when yuo want to squeeze out the last little bit of power possible, running as high compression as possible is a necessity. You can make a lot of power with 9 or 9.5:1 compression, but you will see more gains with higher compression. Unfortunately, the only way to get there is to run gas that doesn't "ignite" so easily. Increased compression increases cylinder temperature (this is how diesels operate) so ignition isn't a problem with the additional resistance to "burn" of the higher octane fuels.

    The problem is when people run higher octane than the motor was ORIGINALLY designed for. Resisting ignition when there is no additional cylinder "heat" IS a waste of time, and has been proven over and over. The lowest octane gas you can run (again, you've still got to prevent detonation) is where you will make the most power.

    The original poster was talking about a 10.5:1 engine. I don't know about the blower aspect, but with crappy (read, pre-Vortec stock heads) combustion chambers, detonation occurs at a pretty low compression ratio. With 91 octane, I'd bet a set of Vortecs or any fast burn chambered head) could be run at 10.5:1 without detonation.
     

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