Mixture ? for Cliff

Discussion in 'The Venerable Q-Jet' started by BadBrad, Jan 24, 2015.

  1. BadBrad

    BadBrad Got 4-speed?

    Cliff,

    Could you briefly render an opinion as to the efficacy of stock '70 stage 1 jetting with today's fuel (91 octane in California)?

    I have:

    • '70 SF block and port matched, small valve, iron heads and iron intake
    • 1-7/8 in primary long headers with 2.5 inch exhaust
    • 118 "style" cam
    • Stock '70 SF, excellent driveability Q-jet with zero bog but obvious secondary engagement
    • Fast curved SF points distributor (with a couple of degrees of vacuum advance in adjustable canister) triggering an MSD 6 box with adjustable timing controller
    • Manual trans combined with rearend gearing rendering 9.39:1 overall in first gear; 2.73 final drive not generally running more than 4,500 max rpm

    I've recently gone to stock stage 1 jetting but wonder if slightly richer (or leaner) might put out more power.
    I don't yet know if this relatively lean mixture will cause detonation in hot temperatures; my timing controller allows me to retard or advance on the fly.

    Gracias!
     
  2. Cliff R

    Cliff R Well-Known Member

    This new fuel doesn't have the energy content of the fuels of yesteryear, so it's not uncommon to have to increase fuel delivery slightly to compensate.

    This is easily done with the Buick carbs, even early unit using the APT system in the baseplate. We try to free up the APT screw in all of the early carbs that we build. This provides the user/tuner full control of part throttle A/F from rich to lean using the correct jets and metering rods.

    Each carb also needs to be set up exactly for the application. If you have changed the engine parameters, bigger cam, less compression, ported heads, tighter squish, headers, free flowing exhaust, etc, the carb is going to need help in other areas more times than not.

    I look a ALL of these things when building carburetors here. It's actually quite rare these days to build a carb for a completely stone-stock set-up. Just about everyone in this hobby is a "hot-rodder", or at least changes one or more items on or in their engine in the pursuit of more power.

    Some folks are pretty good at parts selection, where others end up with combinations that don't work so well. We see it ALL here, so we try to get on board early with folks projects to help them with parts selection. We don't just do carbs here, we build engines, transmission, and tune distributors as well.

    I also support/sponser a LOT of Pure Stock and FAST Class cars, so involved directly with some of the fastest cars like these on the planet.

    https://www.youtube.com/watch?v=Wbv9XJ8FQbw

    As a coincidence we did the q-jet for the 68 FB and the 2 AFB's on the Hemi Roadrunner's 426.

    Anyhow, as it relates to this topic, if the owner/tuner/carb builder supplies us with all the parameters, we can put together a custom kit with tuning parts exactly for what you are doing. I do this every single day, and more of that sort of thing these days than actually working on carbs and other stuff. I have employees doing that for me, but I still get involved with everything that we do here to make sure the final product is as good as it can be.......Cliff
     

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