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Thread: HP 750 & Weiand Supercharger

  1. #1

    Question HP 750 & Weiand Supercharger

    I just installed new 750 HP on my SBC with a Weiand supercharger. Setting the air fuel mixture screw as per Holley recommendation. Only one screw has effect on the idle, but I went ahead and set all the screws as described by Holley. The vacuum reading directly from the manifold is 5 inHg steady in park & drive. The AFR is 11.2 to 12.5 and the exhaust smells rich, but no black smoke. The highest vacuum I got playing with A/F mixture screw is 5.5 to 7.5 inHg, and the AFR is 12.3 to 13. Which vacuum reading I deal with, the steadiest or the highest? The power valve on the carb is 10.5, shall I change it to 2.5? What can I do to get AFR mix between 13.5 to 14? Please help. Thanks.

  2. #2
    Join Date
    Dec 2009


    Quote Originally Posted by mossman View Post
    The highest vacuum I got playing with A/F mixture screw is 5.5 to 7.5 inHg, and the AFR is 12.3 to 13.
    Check the ignition timing advance at idle. Blower (supercharged) engines require more initial timing and less total timing than naturally aspirated engines.
    They also like a short, yet quick ignition advance curve and retarded timing while cranking to start.

    Excessively retarded ignition timing is the most common cause of glowing exhaust headers. Headers glow red because there’s fuel burning inside.
    The two main reasons are a faulty A/F mixture (most likely too rich) and retarded ignition timing; which doesn’t give the fuel enough time to burn
    inside the combustion chamber. Are you sure the ignition timing synchronization is correct (LINK)? (Don Terrill, Former NASCAR Engine Builder - Read Myth #7)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 11.8:1 comp, TFS R-Series FTI ported intake, BBK 80mm TB, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 MT tires.

  3. #3


    Oops sorry, I was in a hurry because the first writing disappeared after writing for about 1/2 hour. OK, Initial timing is 30°, total set at 30° at 3500 RPM.
    Ignition is MSD 6A, distributor is MSD no vacuum advance. Heaviest spring for the advance weight is used. MSD boost retard.

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