How much does combustion vary from cylinder to cylinder and combustion cycle to combustion cycle on a highly tuned engine ?
ANS: In general the more highly modified the engine, the more out of tune the engine will be, even though the engine tuner has done his best. Stock import type engines have the least variation. Why? All the large import engine manufacturers use combustion/intake/exhaust pressure tuning analyzers. Once an engine is modified (assuming without access to a combustion pressure analyzer) the cylinder to cylinder balance and cycle to cycle balance goes astray. Naturally a modified engine will make a lot more power than a stock engine, but every cylinder will run differently and few if any of the cylinders will be optimized. Highly turbocharged engines, carbureted engines, engines with custom intakes, nitrous engines, nitro engines and anything with a Roots style blower all have substantial tuning issues to be addressed.
