hardingfv32 wrote:"Say if the driver is 50% on throttle the engine will "use" the other 50% of the air to burn after the power stroke."
First, this is not really off throttle mapping. As defined in your statement, the driver is clearly at part throttle.
Regardless, in theory it sounds useful for that small amount of time the driver is accelerating out of a turn at part throttle. I just question whether the engine can accomplish such a task. I would think that the fuel and timing would have to be very odd and create some very bad temperatures and possible combustion issues.
Brian
In my thinking, It doesn't have to be off throttle to have exhaust overrun. At part throttle you can deliberately operate the engine at a very low combustion efficiency only giving the driver enough power for traction and the rest is exhausted.
For example, the load requires 200 horsepower and is traction limited.
Throttle input for this load at normal spark timing and fuel is 50%.
Instead with exhaust overrun aided by computer:
*The driver inputs 100% throttle.
*The air delivered to the engine is enough to provide 600 horsepower at peak combustion.
*The fuel supplied to the engine is enough to provide the same 600 horsepower.
*The ECU in overrun mode, retards timing so that the combustion efficiency and the Mean effective pressure is greatly reduced. The engine now puts out the required 200 hp. The other 400hp of air and fuel is sent out the exhaust pipe.
So with this method the diffuser is blown even the driver is at part throttle.
That is what I think happens.. it may not be true though.