Many of the engine packages we have checked the ignition spark timing and air/fuel mixture curves on have had the correct ignition spark timing and air/fuel mixtures for high rpm/wide open throttle operation but need a lot of tuning work at low rpm/part throttle/normal driving conditions. In most cases when an engine is run on a engine dynamometer, they only check for maximum power while using race style headers with open exhaust and they supply the engine with outside air to a carburetor with no air cleaner in place.
The air/fuel mixture and ignition timing curves should be corrected for the real world operating conditions of your cars engine compartment with the hot air coming from the radiator and exhaust system along the changes in exhaust backpressure created by the headers and mufflers you are using which may cause the engine to not perform with the same power that was seen on the dyno.
A properly tuned fuel and ignition system will allow your performance engine to perform up to its potential and will supply you with a better running, more reliable, hot rod! The use of an infrared exhaust gas analyzer and/or an extended range oxygen sensor and then reading the spark plugs (for signs of detonation) is the best way to know if the air/fuel mixture is correct for your engine. Taking the time to properly tune your performance engine's fuel system will not only allow you to unlock all its power, but it may help avoid destroying a expensive performance engine due to a incorrect fuel system tune up. For a more detailed explanation of the use of a five-gas infrared exhaust gas analyzer in fuel system diagnosis on the Web go to: www.automotiveu.com.