elementary manifold vacuum question

[am018]

I suspect you are seeing  a particularly strong 2 cylinder pressure  pulse due
to the combination of  the port design  and the  design of the manifold.

It may not be relevant but in the UK magazine Car and Car Conversions  it has
been  stated  that Weber progressive carbs don't  work well on manifolds
designed for ones on which the butterflies open together and vice versa.

About 130 psi  compression pressure is  fine for standard B series engine.

With siamesed inlets the standard tuning procedure is to open out the inlet port
as far as possible to partly reduce interference between cylinders


Andy Mcf