Category: pistons

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is it a 74 or 80 inch shovelhead cylinder?

One of the most common questions is “Do I have a 74 or 80 inch shovelhead cylinder?”

Shovelhead cylinders are basically the same on the outside dimensions. The bore of the cylinders is however different. Standard size 74″ cylinders are 3 7/16″ or, 3.4380″ and 80″ cylinders are 3 1/2″ or, 3.498″ . Visually it can be hard to tell whats is what, and when you get into 74″ cylinders that are like .040″ over size it is definitely confusing unless you have a dial bore gauge or set of calipers. Calipers can be useful but also hard to get and accurate reading because of dirt and centering them correctly.

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S&S Piston Clearance

I had a set of S&S 92-2500F cast pistons to fit to cylinders and could not find any instructions on S&S’s website, so I looked in my papers and found a instruction sheet. Figured I’d post it up here because getting answers from them isn’t reliable. As long as I’ve been dealing with S&S I have decided they are just fucking jerks these days. Never was like that back in the 80’s.

The forged pistons on this sheet were the old TRW pistons they used to sell. I guess TRW doesn’t make any pistons for them any more, since everything I’ve seen from them for a long time now are made by Wiseco. The Wiseco forged pistons are set up at .003″ piston to wall clearance. As far as the cast pistons go these days I have no idea what they are using. Normally they always have a piston series number on the underside of the piston or box they come in.