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Thread: 825 cfm Mighty Demon Jetting???

  1. #1

    825 cfm Mighty Demon Jetting???

    I just bought a new 825cfm Barry Grant Mighty Demon.

    I am running this car on a RED that is going to be ran at WOT for 1/4 mile racing.

    Being the factory jets that came with the carb are #76 primary and #84 Secondary, should I change out the jets and have them all one size on both the pri & sec sides?

    The carb is running a little rich with this factory jetting. I was thinking of leaving the #76 in the primary and changing the #84's to both #76 on the secondaries so they are all the same and tune from there?

    Is this common to have all the same jetting on a race carb that is running at WOT?

    Any suggestion would be appreciated.

    Thanks in advance

  2. #2
    Senior Member RACING JUNKIE jmarksdragster's Avatar
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    The jet difference is because the front has a power valve that will add fuel at WOT through the power valve channel restrictions (PVCR). DO NOT go down that much. Where is it running rich? Go down on all 4 1 size at a time, and stop when you lose MPH. If it goes down right away, go back up, you want to jet for best MPH. Once you find optimum WOT metering, you can open up the PVCR's and jet the primary down if needed to lean part throttle. Demons also suffer from excessive emulsion, the best way to find out where you are is an O2 system.
    Mark Whitener
    http://racingfuelsystems.myfunforum.org
    __________

    Good work isn't cheap, and cheap work can't be good.

  3. #3
    Senior Member RACING JUNKIE
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    Re: 825 cfm Mighty Demon Jetting???

    Quote Originally Posted by swartzie
    I just bought a new 825cfm Barry Grant Mighty Demon.

    I am running this car on a RED that is going to be ran at WOT for 1/4 mile racing.

    Being the factory jets that came with the carb are #76 primary and #84 Secondary, should I change out the jets and have them all one size on both the pri & sec sides?

    The carb is running a little rich with this factory jetting. I was thinking of leaving the #76 in the primary and changing the #84's to both #76 on the secondaries so they are all the same and tune from there?

    Is this common to have all the same jetting on a race carb that is running at WOT?

    Any suggestion would be appreciated.

    Thanks in advance
    I guess I really don't why you bought a mighty demon for a RED instead of a race demon. The mighty demon is set up to have leaner idle circuit which is not what your looking for in WOT racing, it also doesn't have removable boosters as the race demon does. My advice would be to plug the powervalves and go 84 squared. One backfire when you start your car and powervalves are toast, richen your idle circuit a bit, and you should be ok. Do not go 76 squared!! You will be way to lean. Your starting point should be 84 jets. The powervalve lets more fuel in, so in theory your at 84 squared now. good luck

    Just wanted to edit this in case you didn't know. The might demon only has powervalves on the primaries. That's why the jets sizes are staggered. I meant to type that in and got ahead of myself. Hope that helps alittle.

  4. #4
    Thnaks guys... this is good stuff. How do you plug the power valves?

    As for the O2 sensor what should I be looking for with a A/F ratio at WOT heading down the track? I know 14.7 to one is good for fuel economy but where should I be tuning for?

  5. #5
    Senior Member RACING JUNKIE jmarksdragster's Avatar
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    Every engine has different wants, 12.8-13.2 is average but it can stray a little. What the O2 will do is help you tune it flat in the range you run it in and on the lean side at low RPM's and low loads.

    As for the PV, you can run with or without, you can get plugs anywhere. You then need to jet the primary up to match the secondary.

  6. #6

    825 jetting

    have the same carb. my car launces better with a PV plug in the primaries. as for jetting I run 80 in the front and back at about 75-80 degrees of tempature outside. my carb leans out slighty at higher rpm. It could use different HS air bleeds. the best way to tell is on a chassis dyno with a wide band O2 sensor to get the curve as close to perfect as you can, and save you a lot of headache.

    good luck
    steve

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