Son, you better get yourself some tubs. It's not often that you open up an engine build story by talking about chassis modifications, but with the way Mast Motorsport's supercharged 427ci LS small-block goes about delivering its 917 hp, seriously fat tires and a well-sorted suspension are an absolute must. Before we delve into the specs, we suggest hopping in your car and cinching down that five-point harness. At 6,200 rpm, a stock 427ci LS7 produces 505 hp. In comparison, at that same rpm the Mast LS3-based 427 kicks out a staggering 907 hp. That equates to an 80 percent advantage in power, and the only way to accomplish that given a similar displacement and rpm range is by making 80 percent more torque. The supercharged Mast 427 comes pretty darn close to doing just that, straining the dyno with 817 lb-ft compared to a stock LS7's 475 lb-ft. At the risk of sounding redundant, son, you better get yourself some tubs.

As impressive as the peak horsepower and torque figures may be, what's even more shocking is how much of that output is on tap throughout the entire rpm range. At just 3,100 rpm, the Mast 427 is already producing 743 lb-ft of torque, which equates to 91 percent of its peak output. That's enough to trounce a healthy street/strip big-block. For example, the 532ci big-block Ford in PHR's now-retired Fox Mustang project car—a combo that peaked at 775 hp—was good for just 546 lb-ft at 3,500 rpm and 673 lb-ft at its torque peak. Furthermore, the Mast 427 averages 789 lb-ft between its 3,100- to 6,400-rpm operating range, whereas PHR's big-block Ford mustered a measly 607 lb-ft average torque output. That's the kind of torque that renders half the gears in a six-speed transmission irrelevant, and makes dealing with the size and weight penalty of a big-block a highly questionable proposition.

Make no mistake, this isn't some unstreetable one-trick pony. Mast Motorsports' design philosophy is all about achieving OE levels of driveability and reliability in addition to maximizing power output. Street cars don't run on Q16, so by keeping the compression ratio reasonable and using Mast's own cutting-edge 12-degree LS3 cylinder heads, the supercharged 427 makes its 917 hp on 93-octane pump gas. For a smooth idle quality and street-friendly low-rpm driveability, the engine's 234/254-at-.050 hydraulic roller cam is relatively mild given its commodious displacement volume. Likewise, the reasonable cam duration maxes out the power curve at a moderate 6,400 rpm, minimizing stress on the valvetrain and enhancing durability. So while the supercharged Mast 427 might run like a race motor, it's perfectly suited for a street car—make that a very fast street car. The best news is that anyone can call up Mast Motorsports and order this exact engine combo as a turnkey crate motor.

Big Power, Small Package

Many of today's engine builders report that compared to years past, fewer and fewer hot rodders are opting to build big-blocks. Considering the tremendous power potential offered by modern small-blocks like the LS-series platform, this trend makes a lot of sense, especially in Pro Touring machines where removing weight off the nose of the car substantially improves handling. Not only do aftermarket LS blocks allow for displacement exceeding 500 cubes, there's no shortage of aftermarket heads that can keep pace. Throw a 2.9L Whipple supercharger into the mix, and the result is an insane amount of power in a package not much larger than a wimpy German straight-six. As no surprise, the supercharged Mast 427 takes advantage of the latest in aftermarket block, cylinder head, and power adder technology.

Every motor needs a solid foundation to hold everything together, and this is particularly true when horsepower figures start approaching quadruple-digit territory. Iron is usually the material of choice for engine blocks at this power level, as the distortion associated with aluminum blocks can lead to compromised ring seal and reduced power output. Fortunately, thanks to RHS's LS engine block, fans of the GM Gen III/IV platform can enjoy the durability of an iron block in a lightweight aluminum package. The rugged RHS unit is cast from A357-T6 aluminum, and has proven reliable in 2,000-plus horsepower forced induction combinations. Nonetheless, at 119 pounds it weighs just a hair more than a production LS7 block. For these reasons, it was the block of choice for Mast's blown 427. Mast also builds motors based on the virtually indestructible Chevrolet Performance LSX block with great results, but for this particular build, the nod went to the lighter RHS unit.

A durable rotating assembly is essential to the longevity of any supercharged engine combination, but the parts don't need to be as exotic as you might expect. The beauty of a forced-induction motor is that while they subject the rotating assembly to severe compressive loads, tensile (stretching) loads—which are far more detrimental—are kept in check by keeping peak rpm at a reasonable level. That means that even at over 900 hp, the off-the-shelf Compstar 4.000-inch forged 4340 steel crank and 6.125-inch connecting rods used in the Mast 427 are more than up to the challenge. Billet components would simply be pricey overkill. The same logic applies to the off-the-shelf Mahle 9.45:1 pistons, which are forged from a 2618 alloy aluminum and feature a -25cc dish.