Ive got a h/c setup (see sig for details) on my LT1, running SD.

It seems to me that the extra breathing would require the computer to add more fuel for all of the trim cells. And, in fact, at WOT the trims are locking to positive values, so I think the airflow has definately increased there. However, it seems like in all of the part throttle rpm/map cells (20-70 kPa, 800-2000 rpm)I am getting negative trims -- the computer is having to remove fuel!

I dont understand this. How can I have actually decreased airflow during moderate rpm/map conditions?? Does this have something to do with cam overlap and reversion?

 

The computer is pulling fuel because the O2's are seeing a rich condition. The reason it is setting itself to a positive value (it should be locking at 128) is because it is hard coded in the computer to revert back to the richer condition at WOT for safety reasons.

Now, say the car was running lean and it was adding fuel. The computer would use the last BLM it saw as the BLM for WOT.

It shouldn't be caused by the overlap of the cam because that will cause a "false" lean condition and the computer will add fuel, making it extremely rich.

Is this what you were looking for?

 

Not exactly, I think you are talking about the safety correction the computer uses in PE mode. IE if the last trim used before you go into PE is positive, then that trim is applied on top of the PE afr table. I'm asking more about airflow with a h/c.

This is my basic question:

Is it normal with a h/c to gain airflow in some map/rpm ranges and loose airflow in other map/rpm ranges?

 

I understand what you're saying. I didn't analyze my car with the new setup on the same tune I had on the last one. I don't know if many people do. It's an interesting question to say the least. Maybe the guys in the advanced tech forum would be able more helpful.