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post #18 of (permalink) Old 01-08-2015, 09:48 AM
PSIG
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Join Date: Jan 2008
Location: Seattle, WA area
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Re: 347 Stroker Pistons

Barnett pretty much covered it all, but here's my extra penny of thoughts. The two pin diameters are Ford (.912) and Chevy (.927). The reason is that half of every set of SBC pistons are identical to SBF pistons, due to where the valve notches are. Being able to use a Chevy piston greatly increases your choice of off-the-shelf pistons, and/or allows machinery set-up for them to be used for Fords as-well. Same with the rods. So they make both rods and pistons with both pin sizes to allow this swapping. They also make them all with circlip grooves, so they can either use circlips (floating pin) or press-fit pins, depending on the rod type.

While not as common today, it was often the only choice early-on to resize (pressed pin) or "bush" (floating pin) the rod end to take a Chevy piston that would work best. 30 years ago, SBC stuff was everywhere and sometimes the only choice, much more than today. Mopar pistons had huge wrist pins (.984) and the rod end would get too thin when re-bushing, so they were rarely used unless Mopar rods were also used in certain Ford strokers.

Torque plates and block heating are to allow machining under 'running' conditions. Since the head bolts and head clamping pressure distort the bore slightly when torqued, and a warm engine also changes shape slightly, using torque plates with block heating will give a finished bore that is perfectly round when running. Otherwise, the bore is only perfect when cold if machined that way, and never perfectly round after the bolts are torqued.

This is one reason performance engines can have a very low leak-down (blow-by) compared to a Mom & Pop engine. It's all in the details. I'm one of the anal types, and always use torque plates and heating if the engine is for true performance, racing, or me. If it's just a cruiser that has a lumpy cam and wears a stroker badge for status (typical street car) - whatever. I agree with Barnett that they all run OK in Mom & Pop mode, make plenty of power for that, and do the job fine.

David

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