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Old 12-28-13, 01:31PM   #1
marks73ta
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Default 1958 336 block and crank.

I've been looking thru the old threads here and I see where Pontiac made a small bore 370 block (motor) into a 336 for GMC. Can someone tell me the bore and stroke? I'm assuming the mains will be the 370 smaller 2.56 and uses the 370 stroke of 3.623? To get to 336 ci it would require a bore of about 3.84.
If the '59 is still at 336 using a small bore 389 I would assume they used the 3 inch mains and the 3.75 stroke crank? If so they would need a smaller bore of about 3.78 which are the dimensions of the later 326's.

Does anyone know the actual bore/stroke of the '58 GMC Pontiac block? Did they use the 370 3.623 stroke crank? Did they use the forge crank?
I've been thinking of building a small bore Pontiac turbocharged engine using the thick cast early blocks. This would make a nice higher boost build with the thicker metal span between the bores for gasket sealing. As long as I can find main bearings the smaller ones will run cooler.
Anyway, just playing with some Pontiac turbo combinations. Thanks for any help guys.

Mark L
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Old 12-28-13, 06:12PM   #2
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the 370 was 4.065 bore and stroke was 3.5625.The 347 was a 3.9375 bore with the 3.5625.The 316 had the 3.9375 bore with a 3.25 stroke.Im sure you can search the net for the GMC-Pontiac 336.Tom
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Old 12-28-13, 11:13PM   #3
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Mark
Would be cool if you did the 370 engine and kept it in the 58 GMC truck.
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Old 12-29-13, 12:43AM   #4
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the 58 used the 370 engine with a smaller bore,3.875.Tom
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Old 12-29-13, 10:16AM   #5
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Thanks Tom, I could not seem to come up with the bore for the '58 GMC 336. I see I had the 100ths mixed up between the '58 crank throw and the '58 main sizes. I was going from memory and I should have looked it up first. Old timers disease hits again.
I built my 406 from the early '60 block because it is a lot stronger than later blocks. I was thinking along the same lines using the '58 336 block. Smaller bore, lighter reciprocating weight, wider deck between bores, and the stronger block. Other than the bell housing and starter adapting, it would be a well built easy build. My 406 rotating weight came out at 2000 with aluminum rods. The smaller piston along with a good set of steel rods should still come out at or lighter. This is just a thought experiment. Something I might play with on the side if I can find a good 336 block. Even a '59 336 block would be something to play with. With an even smaller bore but the 3 inch mains, it would open up more options for aftermarket cranks, and good available main bearings. The only problem is the really small bores and matching heads/chambers/valves to that small of a bore. Again, just brain storming.

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