To achieve optimum exhaust scavenging on a four-stroke V8 engine, each cylinder should fire every 180 degrees of engine rotation; on a typical V8 with a cross-plane crankshaft and conventional headers, two cylinders on each bank end up firing consecutively, only 90 degrees apart. The way around this is crossing two primary tubes from each bank over to the opposite bank. For example, on an engine with a 1-8-4-3-6-5-7-2 firing order (with the odd-numbered cylinders on the driver side and even-numbered ones the passenger side), cross tubes from cylinder Nos. 3 and 5, and 4 and 6. Often termed a 180-degree header, this configuration makes the firing cycle seen by each collector occur 180 degrees apart, improving scavenging as well as low- and midrange torque by permitting a smaller collector outlet diameter than normal for a given combination.

See all 1 photos

The problem is packaging this bundle of snakes. Four tubes must cross either under the oil pan or around the front or rear of the engine. On a high-rpm race mill, it may be difficult to keep primary-tube length down to 32 inches or less.

If that's not enough, try to arrange the tubes into each collector so they fire in a rotational firing pattern, as seen on Ford's Indy engines and Le Mans race cars back in the 1960s. Such a rotational pattern further enhances scavenging: The exhaust gas exiting one tube, passing across the opening of the tube directly beside it, creates more signal on that tube than it would on a tube on the collector's opposite side.

In theory, the ultimate solution to the V8 firing-order conundrum is the flat-plane crank (aka, a "180-degree crank"). Essentially, this makes the V8 act like two four-cylinder engines, allowing the optimized collector arrangement of a four-cylinder engine without the need to cross tubes. But flat-plane cranks cause such severe vibration they can only be used on a pure race car.