Intake Manifold

["Pawlak, Joseph A" <Joseph.A.Pawlak@domain.elided>]

Hey guys,

I'm working on eliminating the aggravating situation of intake manifold
leaks which wreak havoc in obtaining the proper air/fuel mixture. I'm
wondering how many of our cars are out of spec to compensate for this
malady. The manifold was originally installed per "the book" and it still
bites one in the butt in having these leaks. (no I am not having cooling
leaks!) Currently I have performed and observed the following. I'm looking
for any additional thoughts on the matter.  

I cleaned up the faces (original casting marks) of the intake manifold using
my 6" blocking sander that is used to , well block out panels for paint
prep. Yes I am being extremely careful about maintaing even pressure as to
no bring the faces out of square. I used 320 grit with a bit of oil and
removed all of the machining marks that were present. Prior to putting on
the heads I checked with a precision straight edge and there was no area
anywhere that I could fit a .001 feeler gauge (smallest I got) under. Even a
bright light did not allow any errant photons to squeeze between the
straight edge and the manifold surface. I bolted one side without gaskets
and there was only one spot I could fit .001 under but not a .002. Now the
question is, that ok? Who knows. I can goof with honing the faces down to
where a .001 won't make it but is it neccessary? 

Without gaskets there is no way the manifold can be bolted down on both
sides, it is just too low down the face for the opposite side to match the
holes up correctly. This does give a opportunity to measure the gap to
extrapolate the amount of gasket material needed to bring closure (cute).
The gap on the other side seems to measure out to around .095 (all the way
around each side so I know I'm running square and true) so our gasket choice
of .050 material is close (2 x .050 = 0.1) Now I question whether .0025
(.005 / 2 = .0025) is enough for gasket compression to seal correctly. I'm
not sure of all the available thicknesses of gasket material. If they had
material that was at .055 that would seem to work great or a 2 x .055 =
.110. So .110 - .095 = .015 that would give an approximate compression of
.0075 per side rather than .0025. I'll check today at lunch since I didn't
make it over there yesterday.

Any thoughts? The success of these experiments will apply to your own
performance improvements. This would make up a cool writeup if it works.

Joe Pawlak
Hampshire Ill
65 Spit, 73 Stag etc.