Jesse Robinson and the crew from SKMFX Engines set out to build extraordinary power from c
What defines a good engine build? For some, nothing matters but the big number on the dyno chart, but just as relevant to us is how you get there. The 417-cube Mopar small-block featured here from Jesse Robinson and the crew at SKMFX Engines in Summerstown, Ontario, Canada, provides a perfect illustration. Built with sights set on competing in the 2012 AMSOIL Engine Masters Challenge, a quick scan of the parts list would have pointed to a mild-mannered street build. The surprise comes when the parts list is put up against the actual power. With 580 hp and 552 lb-ft of torque on hand, the power curve would suggest there has to be something more at play. Frankly, there is, and that intangible element is outstanding execution to get the most out of the parts that went into the mix. Robinson's goal in this build was to use everyday performance parts in a very common configuration, and then work to show the true potential on tap.
In the Mopar world, stuffing a 4.00-inch stroke crank in a factory small-block is one of the most common and popular engine combinations. With the block's tall 9.6-inch deck height, ample crankcase and camshaft clearance, and OEM-length 6.123-inch connecting rods, this is an engine block begging for a longer crank, and it all readily fits in the available space with minimal grinding, reworking, or unexpected hassles. There's no need for a special reduced cam base circle, custom-length rods, or undersized compression height on the pistons. It's simple and straightforward, and that's one of the reasons Robinson elected to go this route. "The general idea was to do a budget-minded build aimed at the average street guy who walks in my door. They never want a stock-stroke build, they always want a 4-inch stroke in a small-block Mopar. The issue is often the project budget and how much cylinder head they are willing to use. I wanted to see how much we could get out of the EngineQuest cylinder head."
A replacement-style Melling oil pump circulates the lube, though it is modified with the p
Adding cubes to the Mopar small-block is a practical approach, given the factory options. The largest Chrysler OEM small-block displacement was 360 ci, leaving big-block swaps as the old solution for stepping up the volume. As Robinson relates, the stroker is a much more practical and cost-effective solution: "The stroker combination opens the door for big cubic inches in a small-block platform. This is a big advantage, providing a bolt-in solution rather than a much more complicated big-block swap." Although these stroker combinations are readily applicable to the small-journal 318 and 340 engine blocks, Robinson prefers the common 360 block as the basis of a typical street build: "I like the larger mains of the 360 block for more journal overlap, which make the crank more ridged with the long stroke." The crank employed is a 4340 forged steel unit from Eagle.
Prepping the production-based block itself was an exercise in simplicity, with a definite lack of trick-of-the-week parts. You'll find the block was given quality machining in the form of basic block prep operations, with attention to detail such as an expert final bore finish performed by Joe Rutters. SKMFX retained the OEM main caps, though ARP studs were added to improve clamping. As Robinson tells us, "When dealing with these power levels, I find the factory two-bolt main arrangement more than adequate for longevity, provided you have good ARP studs and proper machining procedures in preparing the mains. We touched up the center three main feeds for the proper diameter and enlarged the pickup to the oil pump to a half inch."
Providing the shove are common catalog street-style parts, with stock-length Scat I-beam c
With the liberal oil pan rules of the 2012 Engine Masters Challenge, a large custom sump p
The engine relies on a custom COMP hydraulic roller cam, delivering 250/252 degrees durati
The relatively large final bore oversize of .070 inch was actually a result of the bores already being sized at .060-inch over, rather than some quest for maximum cubic inches. To aid cylinder rigidity, the water jackets were partially filled. At .070 inch, the bore accepts shelf pistons for a .030-inch over, 4.00-inch stroke Mopar 340 block, which comes from the factory with a slightly larger bore than the 360. Robinson expands: "The .070-inch oversize is readily available; I chose KB's Icon forged pistons because they have the correct 20.5cc dish size to bring the compression ratio under 10.5:1 with the chamber size being used. I've had good experience with these pistons, and they are cheap and readily available."
Getting the most from a hydraulic roller lifter arrangement with fast-acting lobes takes a
The Icon pistons accept a common 1/16-, 1/16-, 3/16-inch ring package, accommodated by a set of Mahle Clevite rings. Robinson prefers a ring package with the Napier-faced second ring. "I put a Napier ring in the second groove; it's a combination that I have come to really like. If I'm tracking blow-by on the dyno or inspecting the exhaust ports or spark plugs, they are just always sealed up and dry. I think they pick up where the oil ring leaves off."
Connecting the pistons to the crank is an affordable set of Scat I-beam rods. These lightweight forgings are compact at the big end, helping with stroker clearance, and have proven quite capable at the power level considered here. The overall bottom end configuration yields a displacement of 417 ci from the factory 360 block, and is both easy to assemble and affordable. Robinson relates: "The small Mopar is so nice because I only needed to grind very small notches at the bottoms of the cylinders; the Scat I-beam rods with the cap screws aid the clearance. By using readily available parts in a conventional stroker combination, the package offers great value. For just the short-block with machining included without a core charge, I think you can get something like this put together for between $2,400 and $2,800 out the door, which I consider very reasonable for this many cubic inches."