What is Overrun ?
Overrun is where fuel is unburnt in the combustion chamber and leaks past the exhaust valves into the exhaust. The exhaust is normally hot and so the unburnt fuel hits the hot exhaust and explodes creating popping and banging from the tailpipe, many want to achieve this sound. Dependant on the amount of fuel and the setup of the exhaust you may see visible flames from the exhaust.
Overrun is mainly used in high performance applications to COOL internal engine parts, You may think “how I this possible” the fuel only ignites in the exhaust not in the chamber some is vaporised inside the cylinder thurs cooling and taking heat away from parts. The end result leads to audible pops and bangs from the exhaust and possible visible flames.
Remapping and Overrun, when remapping for overrun ONLY the low load sites are changed ie off throttle maps. To achieve effective overrun we must first retard the ignition then depending on the application or client request we may add fuel to further enhance cooling, audible and visual effects.
OEM / Stock ECU remapping for overrun, Most stock factory ECU’s will have the ability to change the ignition timing and fuel so overrun is available to the vast majority of application and vehicles.
For more information on remapping for overrun please contact Super Nova Tuning.