[KevinM]

What is the displacement of your engine? That makes a difference.

Weber's don't like overlap because they have reversion issues. If you only use it for the track, and don't mind blowing a fair amount of fuel back out the tops of the carbs, they can take more cam.

Here is the formula for calculating optimum port (and venturi) size for any engine:

Cross Sectional Area of a Port (venturi):

Area = Volume of One Cylinder (Cubic Inches) x Peak Torque RPM / 88200

Once you have the Area (in Sq. Inches) you divide it by 3.14 then take the square root of the resulting number and multiply that by 2 to get the diameter of a round port in inches. Then multiply that by 25.4 to get millimeters.

There is another formula (actually a “Rule of thumb”) that was developed by Alfa Romeo for sizing webers. This is not as accurate as the other formula and only gives you a ballpark approximation. It is:

Size (mm) = CC’s (of 1 cylinder) x Peak HP RPM x Square Root / 50 (for Venturi size)

48 Webers will probably be too small. 44mm venturis are about the biggest you can go for street use. For track only, where you don't care how they carburate at low RPMs, you can use 46's.

If you need larger than that, look at Gene Berg's line of weber look-alikes that go to 58 mm.

When all is said and done, the Webers will probably give you better midrange and the 4-bl better top end.

Kevin