[Jim c]

In regards to the plate above the webbers.

It could have originated for several reasons.
Having made a few air boxes to me it seems that they might be trying to tune the intake system for top end power.

As the pressure wave from the induction system ( reversion) hits the plate it will send it back into the manifold runner earlyer.
Hence assisting scavinging & cylinder filling. ( getting the relationship between the waves & the intake valve opening periods)

Without the plate the wave passes outside of the trumpet giving the manifold more length basicly.
The higher the RPM the shorter the manifold needs to be.

The type of manifolds they run are pretty hard to shorten , putting the plate on would simulate the same effect.

To conferm this if it was taken off & made more mid range power what you have done is made the intake runners longer in the midrange only.
The reason new engine with variable intake runners is more common these days.

I experianced the same effect on MGB intake manifolds.
I made 13 of them for a customer .Because the eng only revs to 5.500 the manifold had to be farly long & not a lot of room for an air box.

The air box was only about 60mm high & it had trumpets in there as well.
On the dyno it made another 3 hp to the wheels at 5.500rpm but lost 6 in the mid.
Because the waves hit the inside of the lid & went back to early.( giving the effect of shorting the manifold) .
If I took the lid of it was ok.
I did fix it by putting 60mm holes over the trumpets in the lid & covered these with K&N foam.

This allowed the waves to pass in & out on lower rpm & at higher the manifold was the correct lenght.

Sorry if this is a lot of rambling but I think that maybe thats why the plate is there,If not that is the effect it will give.
Jim