Thicker or thinner intake gaskets?????

[LannyL81]

The short story: L81 block was zero decked (actually about -0.006) and I am putting on a set of GM 882 heads milled down to 74cc. I had to use shorter pushrods (-0.150) because the cam I choose was not all that radical and the base circle is about the same as stock....hence the shorter pushrods were needed to get the roller-tip rockers to go across the valve stem correctly.

Now time to put the stock intake on; with stock FelPro gaskets (about 0.070 thick), all the bolts do not go in nicely as they hit the top of the holes in the intake.

So I am thinking that I need to go to as thin a gasket as I can find in order for the bolt holes to align better. Is my thinking correct??? Bolts line up fine with no gaskets.

Thanks,
LannyL81
Tucson, AZ

 

[kiwi vet]

A designer not an engine builder, but that sounds right. By planing the heads you have lowered the inlet bolt holes to the heads - right?.

The only other option if thin head gaskets still to thick, is to take some off each side of the inlet manifold to re-align, sounds a bit drastic though - eh!

Im sure someone will have a REAL answer for this!!! rather than more questions?

Good Luck


PS: If you have bolt alignment problems, won't your ports be mis-aligned as well??? Therefore skimming intake may solve this as well?? Sorry if this is more headache, only trying to help.....honest!!

 

[L48]

How much was milled off the heads? IIRC if more than .030" is taken off you may need to have some work done to your intake. By milling the head you have moved the bolts holes closer to the deck, thereby changing the geometry between the head, the intake and the block. I am not sure if they need to cut the surface that mates to the block, to the head, or both.

Have you talked with the machine shop about your problem?

 

[Jack]

Our local circle track rules mandate production iron heads & a virgin absolutely untouched performer 2101 intake ...except for the bolt holes. Most of our blocks are zero decked and most heads begin as 76cc but milled to 70cc (quite a close shave). Inevitably, the intake doesn't wanna fit ... we are not allowed to machine intakes surfaces ... but we can enlarge the bolt holes in the intake. We simply take a die grinder and "slot" the holes outboard ... we also use a thick intake gasket & plenty of silicone ... especially around the water ports at both ends of the heads. I silicone around ALL ports. Suggest you slot intake holes & dry fit 'til it looks close ... probably take you several dry fits.
JACK:gap

 

[LannyL81]

FINAL

Ended up measuring the bolt interference I had and took the intake to the machine shop. He took off 0.035" from each side. Now it fits like a glove with the stock FelPro intake gaskets. Messed up my powder coating...but had no choice.

Engine almost ready to go into car.

Thanks,
LannyL81
Tucson, AZ