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Thread: experience and opinions wanted carburation

  1. #1
    Ok, my first thread posting. I'm going to do a bit of re-jetting on my Holley and want experienced info input. Why I came here, I dunno, guess I got lost. (Just kidding folks :smile: )
    Here's baseline:
    Engine: 454, .565" lift Hyd cam, RPM Air Gap manifold. stock iron heads.
    Est. by Desktop Dyno 400HP@5000 468lbft torque to 4600. Also running 150HP N2O system (since '78 but not triggered yet on rebuild/upgrades --- break-in)
    Holley 4150, 700 CFM, 66 Pri jets, 76 Sec jets, 6.5" power valve, 30cc pump pri, 50cc pump secc.
    Ran plug mixture & heat range blast yesterday. Mixture looks perfect (slightly lean) and R44T plugs looked just right for temp. Was almost a mile run flat out.
    The orriginal setup ran a stock cast iron manifold & less (factory) cam with the nitrous since '79, never a problem.
    I have discussed some of my planning with a nearby experienced jet man for advice as well.
    Block off power valve, Up jetting 6 sizes (been advised 4 to 6) to 72 and 82. I want to richen up just a tad as a cushion with the Nitrous)
    Run R43T plugs, one step colder than the 44's. The boat has been running 43's perfectly but so happens I had gotten 44's for the WFO run test. Also a cooler plug as a cushion against being a hot spot with the Nitrous.

  2. #2
    Wicked Performance Boats
    Why get rid of the power valves? Nothing wrong with them. In fact they help part throttle cruise mode. They only lean it in part throttle for cruise, when you don't need it. Budlight

  3. #3
    In conferring with DuaneHTP this winter over the re-cam/rebuild about tuning items I could do to maximize my setup, he said I could lilkely pick up some power (& RPM) shifting my setup away from the power valve. Close it off and richen up 4 to 6 on all 4 corners. That's how he runs his setups. I'm looking for anyone's experiences pro/con this way as well.
    I actually doubt the power valve does much on a jet as a jet motor never really sees the high-load-low RPM condition that the power valve is designed to enrich for. The high-load position for a jet is also well into the main metering RPM range & throttle position.

  4. #4
    Wicked Performance Boats
    I was only talking about part throttle operation. and Duane is probably right about full throttle passes. I'm sure he's made a few! Budlight

  5. #5
    Duane's right about the PV's. 4-6 jets to start. You'll probably end up 4 sizes up, but go 6 to be safe. Don't forget...if you run on the rich side, use the hotter plug, and a little more timing. Lean, colder plug, less timing. Frankly, I've found no difference between the two, power wise. Some go one way, some go the other.

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