Small-Block Engine Build - Son Of Sledgehammer

Our plan this month was to build a reliable pump gas street/strip motor centered on the new Enginequest EQ 23 50cc iron heads. These heads target "claimer" race classes that must use as-cast iron heads, but in doing so, Enginequest has provided an unmitigated horsepower windfall for budget-oriented street guys. In this case, the "as-cast" tag is almost a misnomer. The cast finish is so smooth that it emulates the surface finish of an 80-grit emery roll. Translation: The EQ 23 is cast at the factory into a hand-ported shape. With the promise of strong output and low cost (under $250 each, bare), a truly budget bolt-together 350 becomes a reality.

As far an engine building expertise goes, this build was done by UNCC student Dusty Kennet, and it's his fourth engine build, so other than attention to detail, you could duplicate this in your own garage. You'll need some tools, but a little innovation on your part will keep that to a minimum. Chances are you'll be able to come in under our costs by more than $400 because we elected to upgrade the pistons, but that's one of the choices you'll need to make. As a point of reference, we built a similar engine using Enginequest's iron Vortec heads last November. We called that mill the Budget Sledgehammer, and it produced 447 hp for a total outlay of $3,464. In that same vein, we proceed with Son of Sledgehammer, and it's even more potent-and cost effective-than before!

The Game PlanStarting with a pair of EQ 23 heads, we needed to acquire a late-model 350 roller cam Chevy short-block. These are stout cores, so rebuilding one with a bigger hydraulic roller cam looked to be the way to go. For an intake, a race-style single-plane was in the picture, and topping this off would be one of Barry Grant's cost-effective Speed Demon 750 carbs. To light the mix, a PerTronix HEI distributor was used.

Short-Block And TearDownEnginequest is not only in the cylinder head business, but it's also into engine salvage, so we asked the team to locate a late-model 350 short-block for us. To get our block, we logged on to www.aamidwest.com, and put in a request. A few days later, we received a reply, and a price for the style of short-block we were looking for. Yes, it can be that simple.

For teardown, the pan was drained and the oil filter was removed. The engine was taken to a car wash and, along with a bristle brush and a couple of cans of Gunk, pressure washed. Before taking our block to the machine shop, it was given an extensive clean with an electric drill and wire brushes. Time consuming, yes, but this engine will look good when it's done. With the block cleaned, it was taken to KT Engines in Concord, North Carolina.

Block, Crank, Rods, And PistonsPart of the reason for going with a late-model roller block is that it is fuel injected. As such, it has near zero cold-start fuel wash on the bores. This normally means that the bores have little to no wear, and will clean up with just a few passes with the hone. Just to be safe, we bored the block, and scored some new pistons that incurred an expense totaling $437. Like we said before, you'll probably be OK to skip this step.

The stock forged piston with its K-wall narrow ring, and a dish of 12 cc is an excellent package. With a 50cc chamber volume, these stock pistons would've delivered an 11:1 compression ratio with .015-inch thick steel shim gaskets, or 10.4:1 with regular composition-style gaskets .042-inch thick.

But since we opted for an oversized piston, it became necessary to search for something cost-effective that would get us at least 10.2:1, but no more than 11:1. We headed straight to the KB Pistons Web site and found a KB hypereutectic piston (PN 142) would get the job done. At a street price of $237, it would also not break the bank. Part of the reason we went with these pistons is that they utilize 5/64-inch compression rings, which for some reason are much cheaper than 1/16-inch rings. The downside is that performance-wise, such a ring pack is less desirable than the stock one, but in all other respects, it will get the job done. We chose a set of budget Sealed Power rings. As for compression ratio, the KBs, with their 18cc chamber, delivered a 10.35:1 compression ratio.

A couple of points concerning honing if you duplicate this build. If you end up reusing the stock pistons, be aware that the best piston-skirt-to-cylinder-wall clearance for power is about .004 inch. The stock clearances are usually a couple of thousandths tighter than this, so there is usually a good cleanup margin. Also, most replacement rings are made to suit bores up to .005 bigger than whatever is printed on the box. This means a good hone job and some precision ring gapping will get the piston and bore situation right where it needs to be for a minimal outlay. As for the crank, this was in near-perfect condition. KT gave it a finish polish, and it was then ready to go back into service.

Bottom End AssemblyOther than to make sure all our fits and clearances were on the money, little else was done. The first parts to go together were the rods and pistons. The KB pistons come with Spirolocks for pin retention, so you can either go with the stock press fit, or you can have the rods honed for .001 clearance and have a steel-on-steel floating fit. The steel-on-steel floating pin was at one time considered a race-only deal as life was limited, but these days modern oils have changed that. There is little cost difference between getting the rods honed, and having the machine shop do the press work for a press-fit pin. The advantage of a floating setup is that it is easier to replace pistons should this need to be done at a later date. We went the floating-pin route.

The next step in the assembly procedure is to gap the rings. The end gap for hypereutectic pistons is different than for forged pistons, and the appropriate gap needs to be determined from the piston or ring manufacturer's instructions.

The first components to go into the block are the main bearings and crank. As is often the case, novice engine builders just assemble these parts and assume that the clearances will be what they are supposed to be, and that's a bad move. The reality is that most bearings produce a satisfactory clearance for typical street use, but it is common to have a combination of off-the-shelf bearings and main bearing housings that produce clearances on the tight side. This is not good if you intend to run up to 6,000-plus rpm. This means checking the bearing clearances to make sure they are right. For the mains, we wanted to see a minimum of .002, and preferably .0025 inch.