One more comment on intake manifolds & race results.   Do not ignore the benefits of a really clean air inlet with ram air recovery BEFORE the manifold.   At 1125 ft  msl, 220 IAS, I saw manifold pressures around 31.8" Hg.  Ignore this factor and you throw away about 6% "free" horsepower.

 

Al,  I forgot to comment on your last note about your MAP tap in manifold.  I think it is highly possible you were seeing errors induced by air stream eddies or some other unpredictable factors caused by that location.   It is a challenge to get MAP measurements when you have no real plenum, only runners with high velocity air.

 

Tracy