Jetting Rule of Thumb?

Discussion in 'Holley' started by Johnny Angel, Sep 24, 2009.

  1. Johnny Angel

    Johnny Angel Well-Known Member

    I have a Holley HP1000 on my car. It is jetted 82 Primary and 83 Secondary, with jet extensions in the rear, that came with the carb. I am running stock power valves front and back.

    My question is, if I wanted to jet down for w.o.t. a/f ratio, I would just probably jet the carb square, at 82's all around. If I wanted to jet up, would I just jet it square all around to 83, or should I just jet up on the back, to 84? I know square is probably ideal, and have heard I can run carb, with (4) jet sizes difference, between the front and the back. I.e. 82 front, 86 rear, while using the power valve setup.

    If I like the cruise a/f ratio as is, and I want to richen it up, I should just keep going bigger in the back right?

    If I want to lean it out at w.ot., I should reduce the rears, but never lower than the primaries right? At that point, I should try to lower the primaries, staying in the safe zone, then add or subtract from the secondaries from there? I know that 12.0 to 12.8 or so is safe for w.o.t., what is the range I should be looking for for the cruise a/f ratio, to make all this come together? Thanks for the help.

    John
     
  2. shiftbyear

    shiftbyear Well-Known Member

    I DON'T THINK THERE IS AN EXACT RULE, AND TUNING A HONDA AT CRUISE AND A BIG BLOCK BUICK MAY COMPLETELY DIFFERENT. A/F RATIOS CAN ALSO BE CONTROLLED WITH AIR BLEEDS, OR FUEL LEVEL. IF YOUR GOING TO BE SPLITTING HAIRS TO GET THE BEST CRUISE A/F RATIO YOUR PROBABLY NEED SOME CHASSIS DYNO TIME, A SELECTION OF JETS AND AIR BLEEDS, PLUS A FEW DIFFERENT SPARK PLUG RANGES. ALSO CALL HOLLEY OR BARRY GRANT TECH LINES. SPARK PLUG READING IS VERY HELPFUL IN FINAL TWEAKING. GOOD LUCK
    http://www.4secondsflat.com/Spark_plug_reading.html
     
  3. Johnny Angel

    Johnny Angel Well-Known Member

    Thanks for the link. Great info on that site. I will have to pull my plugs and give them a look see.

    John
     
  4. BillyBoy

    BillyBoy Well-Known Member

    Hi John,

    I'm running a holley this year too. It took quite a while to get it to where I'm happy.

    If you are happy with how it drives on the street, leave the fronts alone and just change the back to adjust WOT. Don't worry too much about the spread between the front and the back. I would also recommend pulling and plugging the rear power valve and upping the rear jets 6-8 sizes. The rear power valve can get uncovered on hard acceleration (IE why there are jet extensions on the rear.)

    For AF ratio, 12.0 is rich for WOT. My car slows down about 2-3mph when it's that rich. I try to get close to 12.6 for WOT when running pump gas (10% ethanol). I would go closer to 12.9 if I had gas without ethanol. But at the track, the best way is to try a watch the MPH in the traps to find the best jet.

    For cruise, you really want it to be between 14 and 14.7 and then dip down into the 13s on gentle acceleration. Good luck with that. Mine is still way too rich on the highway. If it would quit raining, I might be able to work on it some more.

    I also have been working on the the accelerator pump tuning which has really helped my 60ft times. That's probably the biggest advantage the holley has over the q-jet.
     
  5. Johnny Angel

    Johnny Angel Well-Known Member

    Thanks Bill. I have also posted a more clear explanation of what I am dealing with, in the street/strip section. I have gotten a little help from a friend with a wide band, and he found that I have between 12.0 and 12.5 on w.ot., but the cruise is where we are really fat. 11.0 to 12.0, or there abouts.

    I am running 82 fronts and 83 rears now, can I just lower the fronts and raise the backs, untill I get the cruise I want and keep the w.ot. between say 12.3 and 12.7? (i.e. 80/83, 80/84, 79/85 etc.) I realize then, I would need to play some at the track to optimize the mph between 2 to 3 sets of rear jets. Am I thinking in the right terms?

    Are you going to Cordova? I am going to try.

    John
     

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