Need Help! Choosing right size race carbs.
 

Hi Gang!

I am finally realizing a dream of owning my own race car and have purchased a 1970 911S. I am running a fairly stock 3.0L motor and am really torn about what size Webers to use with it. It will be a track only car, 100% race. Should I use the fairly standard 40MM Webers, or a larger 46MM? FOR NOW, I will retain the stock CIS pistons and cams (budget). I has straight headers and megaphones on it. Car weighs in at about 1950#.

Some shops tell me 46's will be to large, others say 40's will be to small as I build up the motor later.

Thanks!

Chris
'82 930
'70 911S

Chris,

Bruce Anderson says 40 IDA-3C carbs an 34 mm venturis are perfect for a 3.0 engine. But, you can always run through the math yourself, if you like crunching numbers!

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Warren Hall
1973 911S Targa

Yah.. I've read Andersons book and fiddled with the math too... Anderson specifically talks about compromises needed for street cars and to be honest with yourself. He really doesn't speak to the effect of 46's. I assume the power would be peaky, but it IS a track car staying above 4000RPM most of the time...