Heavy Breathing 101The 10 most powerful American engines can all be described as heavy breathers. Put simply, the more air an engine can swallow in a given time period, the more power it generates. In effect, engines are air pumps.
Several important variables affect engine output: size, or displacement; compression ratio; engine speed; and volumetric efficiency.
A larger-displacement engine is like a bigger hammer. In this powertrain lineup, the 8.0-liter V-10 is Thor's own nail-driver. Remember the old adage, "There's no substitute for cubic inches"? Displacement is the volume of the cylinder from the bottom to the top of the piston stroke. The "smallest" displacements in this group are the 4.6-liter engines in the Cadillac DeVille Concours, Lincoln Mark VIII LSC, and Ford Mustang Cobra-they're at or less than 280 cubic inches apiece.
Generally speaking, the higher the compression ratio the better, assuming the engine's running on knock-resistant high-octane fuel. The compression ratio is the relationship of the cylinder- and combustion-chamber volumes with the piston at the bottom of its stroke, to the volume at the top of the stroke. The higher the ratio, the more the air-fuel charge is compressed.
The Viper, for example, has a fairly easygoing 9.1:1 ratio. But remember, it has all those cubic inches working for it. The Corvette Grand Sport takes full advantage of its premium-fuel's knock resistance and electronic knock detection to squeeze its air-fuel charge with a 10.8:1 compression ratio.
The 4.6s run relatively high compression ratios thanks to good combustion-chamber designs and excellent thermal efficiency. The Mustang runs 9.9:1 and the DeVille is all the way up at 10.3:1. Not bad for a luxury four-door sedan.
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