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308 Weber Venturi diameter

Discussion in 'Technical Q&A' started by cavallo_nero, Feb 9, 2004.

  1. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
    1,656
    colorado
    Full Name:
    Giovanni Pasquale
    Has anyone increased the choke venturi diameter in the weber 40DCNF?? i have a 32mm and am thinking of going to 34 or 36. my car is running pretty lean at hi rpms with 135 mains and 185 AC jetting. i live at 7000 feet above sea level. my 308 is a euro spec with euro cams, hi comp pistons, electromotive ignition and a dual exhaust. i will most likely bump up the mains to 140 if i do increase the venturi. how much will my low end power suffer if the venturis are opened up a bit like i mentioned. i thought i would have to lean my car out considerably being at high altitude, but with all the mods, cavallo wants mo fuel..according to the dyno results....stock euro jetting on my car was 125 mains, 200 AC. thanks
     
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  3. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    Yes, the combo of 34mm venturis and 140/145s with 190 or 200 A/C works fine in many cars (all cars are a little different, and the 7000 ft altitude will make a difference). A Forza article actually found that 34s maximized top end hp on a 308 2v. May want to get on a dyno ($50) to verify A/F once you change jettings, and shoot for about 13.2 +/- .5 Air/Fuel ratio (test with filter installed). You will note some low end loss of response, but not too much typically.
    FChatter Philip Airey, running P6 factory comp cams, actually is on a 36 mm venturi. He may be better able to direct you.
    Good luck
    rt
     
  4. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
    1,656
    colorado
    Full Name:
    Giovanni Pasquale
    thanks rt, do you know philips handle BTW. i remember him from the ferrarilist. and yes, the dyno is the way to go, but it is a bit more expensive, $75 for just a setup fee - but well worth it.
    john
     
  5. snj5

    snj5 F1 World Champ

    Feb 22, 2003
    10,213
    San Antonio
    Full Name:
    Russ Turner
    John
    Try pma1010
    best
    rt
     

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