[traindriver]

I'm in the process of switching over to a 4x 48IDA setup for my 351W. I wasn't happy with the pre-done kits so I'm going to build my own. In designing the linkage I was looking the typical side pull systems. Typical of webercarbsdirect.com kits and some but not all others.

For back to back or front to front carb mounting, these systems typically use a side mounted bellcrank and then a rod to the topside mounted lever of the left carb bank and then a second rod to a bottomside mounted lever on the right bank carbs.

I built a kinematic computer model of the linkage and measured its ability to move the left and right bank carb levers equally. The results were fasinating. Although it looks as though the linkage would move the levers identically, they don't, in fact the error at half throttle can be over 7 degrees. that works out to a 25% cross sectional area difference in the throat!! Here's a graph of the results, the dashed line is a perfect linkage, the solid line is the side pull linkage. Bottom line, for a front to front or back to back set up, use a centrally mounted bell crank, which BTW needs to be very accurately centered particularly down the axis of the motor...but that's another analysis.

A graph of the results is attached along with the linkage model.

The reson for the big error in the side pull, look at the approach angle of the linakge rod to each lever, one is acute the other obtuse. The tangential component of each displacement vector when the lever is moved is different.

If you have Webers you know Cal Metal's favorite point, it's usually not the carbs but rather the linkage.

Food for thought if you're battling your Webers.

Regards,

Chuck
SP1591