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Ron Earp · 12-19-05, 11:03 AM

Hi Mike,

A buddy of mine that does a lot of Porsche stuff just came in with some documentation from Weber regarding venturi diamter and engine size/RPM. To calculate the size it says to use this formula:

Venturi size in mm can be found with:

20 * SQRT ( (V/1000) * (N/1000))

Where V is the volume of one cylinder in mm and N is the RPM where the engine makes peak horsepower.

I ran this formula for my engine, 5.6L (342) and 7500 RPM peak power and came up with 45.85mm.

It also goes on to say that Weber suggests that the throttle bores be larger than the venturi by 10 to 25 percent. So, a 44mm choke in a 48mm IDA would be as big as it could get.

12-19-05, 11:03 AM	#16 (permalink)
Ron Earp Ron Earp Site Administrator Join Date: Sep 2001 Posts: 3,891 Rep Power: 54	Re: TWM/Weber manifold flow Hi Mike, A buddy of mine that does a lot of Porsche stuff just came in with some documentation from Weber regarding venturi diamter and engine size/RPM. To calculate the size it says to use this formula: Venturi size in mm can be found with: 20 * SQRT ( (V/1000) * (N/1000)) Where V is the volume of one cylinder in mm and N is the RPM where the engine makes peak horsepower. I ran this formula for my engine, 5.6L (342) and 7500 RPM peak power and came up with 45.85mm. It also goes on to say that Weber suggests that the throttle bores be larger than the venturi by 10 to 25 percent. So, a 44mm choke in a 48mm IDA would be as big as it could get.