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Car Craft Engine Build & Comparison - Battle of the Titans: Chevy 350

Photography by Terry McGean

Next, Sal ran the block through the hone. The Speed Pro pistons were measured prior to firing up the rig to determine exactly where the bore diameter should be when finished. According to the enclosed instructions, the anti-scuff coatings on the skirts of our Speed Pros must actually be taken into consideration when measuring the pistons, since the coating itself will make the pistons seem extra large for the intended bores. However, those measurements can be misleading, since the coating is not actually part of the piston; it's soft and will wear with time. JMS uses these coated pistons often and sets the hone accordingly.

While the block was being prepped, JMS's Howard Allen was inspecting our crank, and as we'd hoped, it only needed to be polished. After Howard had the journals looking as if they were chromed, he remeasured to verify the dimensions, and as predicted, it was still well within standard spec.

The techs at Federal-Mogul told us that the H100CP hypereutectic pistons we were using were intended as a performance application, which meant (among other things) that they shouldn't fall too deeply into the bores at TDC, like most "rebuilder" pistons do. Their estimate placed the piston 0.020-0.025 inch "in the hole" with a mild skim of the block decks. Since we planned to run 64cc Vortec heads and 0.015-inch steel-shim head gaskets, that would give us around 10.5:1 compression and sufficient piston-to-head clearance. Sal performed the minor decking, which took 0.007 inch from one deck and 0.009 inch from the other (to even them out). Later, we mocked up the short-block and found the pistons to be 0.024-inch down, giving us 0.039-inch piston-to-head clearance (Federal-Mogul says 0.035 is the minimum) and a calculated 10.4:1 compression.

Having the stock connecting rods reconditioned would have cost about $80, and we'd have wanted to upgrade the rod bolts, which would've added another $40-$50. Instead, we opted for a set of used GM powdered-metal rods from a late-LT1 engine. Chevrolet says they are stronger than the factory pink rods and have high-grade fasteners. Best of all, we could purchase them for the same dollars that would have gone toward reconditioning the stockers. Notice the lack of a balance pad on the big end--GM felt these rods were so uniform that the pad was unnecessary. Indeed, ours checked out to be within 3 grams of each other, but the JMS crew shaved them to a perfect match anyway.

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