Say your airflow meter is a 5volt output type. Boost cut is at 4.2volts which is 100% duty cycle of the injectors.
(0 Volts is 0% duty cycle)
At the factory they deliberatly put a safety margin in. For example, stock toyota(and all manufacturers) run really rich air:fuel ratios on full boost like 10.5 or 11:1. The 1JZ is famous for it.
This is too rich too make good power but it is safe to prevent detonation and lean out so engine's arn't damaged by morons.
Now with the injectors already at 100% and you go past boost cut with your FCD no more extra fuel can be added but this is ok up until a point. That point for turbo cars is around 12.5:1 air fuel ratio for turbos, any leaner and detonation and high exhaust gas temps becomes more likely.
FCD's are a good thing because they will allow you to run more air(boost) into the engine before it cuts out which brings up the air fuel ratio to a more power productive level.
On the LS1 holden engine they run a/f ratios to 10.5:1 which is ludicrously rich! By simply pluging in an aftermarket air flow meter with a skewed output voltage a/f ratios are instantly lifted to 12.5:1 and 20Kw gain is instantly seen at the wheels!
Sat, 31 May 2003 06:11
