The inline-6 engine isn't the only configuration with perfect balance. Boxer engines, regardless of the cylinder count, are also inherently balanced, and the same is true for V12 engines.

Then there's the straight-six engine, fitted in only 3,513 drop-tops that year. This one has the 250-cubic-inch (4.1-liter) L22, which was one of two six-cylinder mills available in 1968.

Under its hood sat a 3.6-liter inline-six engine with 276 horsepower and 284 lb-ft of torque. This helped Mercedes compete with BMW's E36 M3, the first BMW M3 to use a six-cylinder engine.

The engine is stamped 18N411381 and V0208MO, which, when put together, suggest this is a numbers-matching 1968 Camaro Z/28 fitted with a 302ci V8 engine built on February 8, 1968.

A semi has room to spare for a long, tall inline-6, but will always be limited in how wide it can be. One trade-off of an engine with a long stroke is that it can't turn fast RPMs like a high ...