Reply to "4 x Weber 48 IDF (not IDA) conversion"

> look at the size of the Weber venturi times eight, then do the same
> on a 750, 850 or larger Holley...the volume flowing through the
> Webers will be greater how there can be restriction I don't know.

Each Weber barrel on an independent runner manifold operates
intermittantly, only when that cylinder is on its intake stroke.
With a plenum underneath the Holley 4 barrel, the carb operates
continuously as there's always an intake stroke somewhere in the
plenum providing a positive pressure differential.

> Yes. I agree with you guys about the Webers. The cfm of a set with
> 42mm chokes is actually around 2400 cfm.

For equivalent flow, an IR carb needs to be roughly 3 times the
CFM rating of a plenum carb, for the reason noted above. This
varies somewhat with the type of plenum. A split plenum intake
like a dual plane requires more carb (rated) flow than an open
plenum single plane does.

> The Holley chart can not explain why they work when a single 4v
> of around 715cfm is sufficient to 8000 rpm on a 351.

Because an implicit assumption of the Holley chart is a plenum
intake is being used. Put 2400 CFM of Webers on a plenum intake
and they wouldn't work well at all. On an IR intake, they do.

Dan Jones