carbs

[pcar9119]

Does the taper in a venturi need to be there. and if so how much is a required amount. the way it's taperd would actually seem to slow things down, not speed things up.?? thanks

[911pcars]

The tapered area is the venturi that creates the low pressure area that allows fuel to flow from the float bowl into the carb throat - principle courtesy of Joseph Bernoulli who discovered the phenomena. Air speed actually increases once past the venturi.

This is the same principle that allowed the Wright brothers plane to not crash at Kittyhawk in 1903.

Larger carb. venturis will ultimately pass more air and create more power, but because of the larger passage, a higher signal is needed to create fuel flow, hence weaker low speed throttle response.

Carbs have been on 911s for eons so the recommended venturi size and jet settings for your application and driving conditions are just a few keystrokes away.

Sherwood

[pcar9119]

so what does that mean. do you know how much taper i should have .

[911pcars]

Originally Posted by pcar9119

so what does that mean. do you know how much taper i should have .

I'm saying the venturis should have a venturi shape to them. If not, I'd guess the venturis are too big for anything short of an out and out track car.

I hate to tell you perform a search, but if you haven't yet, you're probably resisting for some reason.

The recommended venturi size depends on factors such as engine displacement, camshaft selection, jetting, planned operating conditions, altitude, etc. There is no "one size fits all" set of venturis unless you're expecting performance that's less than ideal.

That said, I recommend uhhh 30-36mm venturis. You can take my word for it (don't), wait for others to chime in, or look it up in the many charts people have contributed for the past 35 years.

I'd make your task easier with a ballpark chart, but I'm not at my main computer.

Sherwood

[pcar9119]

thank you for your response. I understand what you telling me, but is there some formula to figure out how much taper needs to be in the venturi. Do do you buy chance have a 32 or 34 venturi lying around you could measure for me or take a pice of so i could see the actual thing? I know i should be around a 32 to 34 venturi. thanks for your help

[911pcars]

This took me about 1 min. to find:

Porsche 911T Weber venturi parts

Porsche 911T Weber venturi parts

Misc 911 Parts Some early stuff too

Weber IDT's

Weber 32mm Venturis from 40IDA Carbs

Hope this helps. As for the exact dimensions (you going to make some?), that's something you'll have to find on the internet. Look under carburetor venturi and Bernoulli.

Sherwood