The Pro Comp as-cast head came complete with a 2.25/1.88 stainless steel valve combination
Our Gen-IV 454 pulled from a one-ton work truck was equipped with the desirable four-bolt block, but the reciprocating assembly was a combination of a cast crank, forged rods and cast pistons. Naturally, the lack of forged components worried us, especially the pistons, but we had full confidence in the stock crank at our intended power level. Given the lack of forged internals, every precaution had to be taken with regard to the tune, lest we blow our low bucker to smithereens.
The factory pistons presented another problem in the form of piston-to-valve clearance. The low-compression, dish-top pistons featured valve reliefs designed for the 2.06/1.72 valve combination used on the factory (iron) peanut-port heads, not the larger 2.25/1.88 valve package in our Pro Comp heads. Knowing we needed a healthy cam to reach our goal of 500 hp with the low-compression 454, we mocked-up a pair of cams using the Pro Comp heads and factory pistons prior to assembling the motor. Since we did not have access to the Summit cam we planned to order for this build up, we did the next best thing. We tested P-to-V with a pair of Comp cams, one larger and one smaller than the cam we planned on purchasing from Summit. The smaller XE274H (flat-tappet) cam fit with a minimum P-to-V clearance of 0.115, while the larger XE284H cam snuck by with 0.065. This meant the Summit grind (0.540 lift, 238/248 duration) would easily fit. Running wilder cam timing (like the Comp XE284H or larger) would require use of the Isky valve-notching tool to add the necessary clearance.
The small valve reliefs in the factory pistons and larger valves in the Pro Comp heads req
The next obstacle was ring seal. A visual inspection and leak down of the motor indicated that it had been run hot sometime in its long life. While we hoped to simply install the new cam, heads and intake on the used short-block, it looks like this particular motor required a bit more attention before final assembly. Due to our budget, new pistons were definitely out of the question, but we elected to install a cheap set of rings after a quick hone to break the glaze. To keep costs down, we honed the cylinders ourselves using a flexible ball hone. The only costs associated with this adventure were the new rings and a couple of cans of brake clean, engine degreaser and Chevy Orange spray paint.
While we had the pistons out, we decided to scrape off the years of grease and paint the block. We also hit the tops of the factory pistons with a wire wheel to clean off the oil and carbon deposits (though this reduced our static compression). We wanted a nice, clean surface to minimize the chance of detonation once we hit the nitrous. When we had the block painted, the pistons cleaned and the new rings installed, we reassembled the short-block using the original bearings. Naturally, we'd strongly recommend a complete rebuild (using the stock crank), but this story is for those who accuse us of not speaking low-buck here at Super Chevy.
The awaiting short-block received the hydraulic flat-tappet cam from Summit Racing (K-1303) using the stock timing chain. Again, we'd recommend replacing a high-mileage chain with a new double roller version, but sacrifices had to be made to appease the low-buck gods. The engine was assembled using the low-buck gasket set from Pro Comp with the exception of the head gaskets. We stepped up to a set of Fel Pro 1027 gaskets designed for the Gen-IV block. The complete gasket set from Pro Comp included head gaskets, but the gasket set was designed more for a stock rebuild than performance usage. With nitrous use, we felt better stepping up to the Fel Pro head gaskets (which offered improved cooling passages compared to the Pro Comp set).
After installing our new rings and old pistons (the bearings were reused), on went the ass
Using the Fel Pro head gaskets and Pro Comp head studs, the aluminum heads were torqued in
The hydraulic flat tappet cam and lifters (PN SUM-K1303) were purchased from Summit Racing
The assembled Pro Comp heads featured adjustable guide plates (important for proper pushro
This combination of used HEI distributor and plug wires was purchased from the Pick-a-Part
The engine was run on the engine dyno with only a Meziere electric water pump. Running the