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#1
04-18-2023, 11:59 PM
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70cc swap to 55cc head (gasket thickness needed to keep same c/r)
408 ci
thank you |
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#2
04-19-2023, 12:26 AM
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So you’re starting out with let’s say a .040 gasket that’s probably about 4.30” in diameter.
That’s around 9.5ccs. So to add another 15ccs you need another roughly .060” for a total of .100” to .110” gasket thickness. That’s a mighty thick head gasket. I wouldn’t do it this way, I’d be buying some new pistons with a 15cc dish. I know you’re a RAV guy and I’m assuming you’re wanting to run some RAV 303 heads. Do it right and either put a dish in your current pistons if they’ll accept it or change the pistons out.
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1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
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#3
04-19-2023, 12:29 AM
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If I didn't fat-finger the calculator-
You need .066" more gasket thickness than previously.
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Anybody else on this planet campaign a M/T hemi Pontiac for eleven seasons? ... or has built a record breaking DOHC hemi four cylinder Pontiac? ... or has driven a couple laps of Nuerburgring with Tri-Power Pontiac power?(back in 1967) |
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#4
04-19-2023, 12:33 AM
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Quote:
Might be a ping monster. Most heads that I have seen that are 55ccs are race heads with 2,25 valves and they will not fit on a 4.150 bore. What kind of heads are your 55cc heads ? |
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#5
04-19-2023, 07:01 AM
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I have an engine with .140” thick cometic head gaskets and thicker cometic intake gaskets too match. Not a Pontiac though. The intake gaskets might be an issue, I don’t recall what Cometic carry’s for thicker intake gaskets for Pontiacs. If you are going to have to stack factory type gaskets you will want to do some calculating and get the head gasket thickness correct to match the intake gasket height up. It isn’t cheap, but it is doable.
You need have a starting compression to figure your question out, because the difference change’s as the compression gets higher. 15cc head swap starting at 9.5:1 changes the compression LESS than if you are starting at 11:1. Last edited by Jay S; 04-19-2023 at 07:07 AM. |
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#6
04-19-2023, 07:24 AM
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What heads are these?
If there Aluminum they could all use some chamber unshrouding on the plug side to the tune of 6 CCs and then you could use a far less thicker head gasket You could even grind or machine in fuel sheer trips which I feel many of them need.
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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
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#7
04-19-2023, 08:30 AM
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...got a pair of new Cometics 4.20" holes and 0.080" thick hanging sealed, unopened on the wall Just sayin. Paid over $300
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#8
04-21-2023, 02:21 AM
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thank you folks
your right B- MAN
303 V head to replace 400 V head .030 400 12.4ish c/r ricondas old V motor motor runs great/cold with good oil P. may need heads sent out for a freshen further wrenchin required sounds like you folks are around .100 head and deal with intake gaskets . |
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