America's Most Powerful

The higher a given engine can comfortably rev without bending or breaking the crank, pistons, rods, or valve train, the better. Think of pumps spinning at greater and lesser speeds; the big pump in this group, the 8.0-liter Viper engine, makes its 415 horsepower at an almost lazy 5200 rpm. The smaller 4.6-liter GM Northstar must reach 6000 rpm before it makes its 300 ponies, and the Cobra's engine spools just a few ticks less at 5800 to make 305 horses.

Volumetric efficiency is the final variable in the power equation: How good is the engine at pumping air as the speed increases? Just think of the air as a liquid when volumetric efficiency is considered. At slower engine speeds, the cylinder fills completely as the piston drops in the cylinder. But as engine speed increases, the inlet port stays open for less time, meaning there's less time for the cylinder to take its gulp.

The variations of the GM 5.7-liter illustrate this well. Horsepower from these similar engines varies from 260 in the Impala SS up to 330 in the Grand Sport. The big difference is higher volumetric efficiency at elevated engine revs; the Grand Sport breathes better thanks to bigger intake and exhaust valves and a high-performance camshaft with increased lift, duration, and overlap.

Chevrolet Camaro Z28 SSStarting in '92, Ed Hamburger's Street Legal Performance (SLP) carved out quite a lucrative niche by offering power-enhanced Firebirds, known as SLP Firehawks, through Pontiac dealers. For '96, Hamburger has collaborated with the folks at Chevrolet to produce the Camaro Z28 SS, which will be sold through Chevy stores. As with the Firehawk and Ram Air, the SS' OHV LT1 extra punch comes from a revised air-intake system. When the engine is equipped with the optional exhaust system, SLP claims a peak of 305 horsepower. Also included in the SS package: a composite hood, 17x9.0 "ZR-1-style" wheels fitted with BFGoodrich Comp T/As, and SS badges. With help from the optional Torsen limited-slip differential and the sport suspension package (Bilstein shocks, progressive-rate springs, and revised rear lower control arms), we ripped off a Cobra-defanging 5.3-second 0-60-mph sprint. Where the new Cobra feels zingy, the Z28 SS feels brawny. Where the Cobra is ready for elegant motoring, the Z28 SS is ready for a street brawl.