Guys,
Quick question.....will there be any "mis-match" situation with running a 1970 455 manifold on 6X-4 heads? .....like exhaust crossover etc.
Thanks.

Guys,
Quick question.....will there be any "mis-match" situation with running a 1970 455 manifold on 6X-4 heads? .....like exhaust crossover etc.
Thanks.

yes

for stock intakes you needs to use a 72-79 intakes. or use an aftermarket intake

You can run the Felpro gasket that has a block off insert that covers the exhaust cross over (both complete and open for the early heads).

Thanks very much....I don't have the heads yet...they're on the way. I had a sneaking idea that there may be a problem.....I'll look up that Fel-pro gasket. Thanks.

You could also fill the siamesed ports and you would have no problems.

I blocked mine off with a thin piece of stainless steel cut from some trim on a Grandille.

Felpro 1233 is the gasket Big Injun mentioned. I've use it on both my cars for several years and haven't had any problems yet.

would I need to do the same with 16's (heads) from a '69 using a '74 intake?

no they should work, but why use an EGR intake. I would try and find a 68-72 intake instead.

I've used that 1233 ..and both times it burns through eventually i use a aluminum block off pplate now...works great!!!

OK, so if I understand the mis-match situation properly, could I fill the blind hole above the exhaust crossover in the head and just use the regular 1970 felpro intake gasket? I'm not concerned about blocking off the crossover as such...just about any leak problems.

the hole is there to keep the heat of the center exhaust away from the oil under the valve cover. that would work, but I wouldn't advise it.

The 1233 gaskets will not match up to stock intake ports, they are designed for RAIV ports. It is easiest to just fill the upper hole on the passenger side with JB Weld/Epoxy, then use standard intake gaskets. This can be done without removing the head.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Leigh:
OK, so if I understand the mis-match situation properly, could I fill the blind hole above the exhaust crossover in the head and just use the regular 1970 felpro intake gasket? I'm not concerned about blocking off the crossover as such...just about any leak problems. </div></BLOCKQUOTE>

YES!!

When I put the 1233s in, I didn't use them to block off the crossover, I used them to match the late heads and early manifold. They work fine for that. I would not use them as a blockoff--I would use the thin plate. They fit my standard heads and manifold ports just fine, though. No worries.

Thanks very much for all the info guys. I'm straight on it now. I just needed to get this right as I have to order all my stuff in advance as its difficult to buy Pontiac specific parts here in Australia.