WOT max HP tuning question

[SidWell]

MSII with EDIS: Under a wide open throddle condition and the spark advanced to a point where any more advance will not burn any more fuel, does the engine need a different AFR for one RPM and a different AFR for a higher RPM? I know this is an awkward question so I will restate it: Assuming an engine is running at wide open throddle, making max horsepower with an AFR of 12.8:1 @ 2500 RPM. but at 4500 RPM and WOT will the AFR requirement change for max horsepower?

[cygnusx1]

    Yes and no, it might and it might not.  That's why the most precise tuning can be done on a dyno that can hold a set RPM.  You set the dyno to hold 2500rpm, for example, and move the throttle from load point to load point (kPa) while tweaking the AFR for max power in each load point.  The cam and flow harmonics will make fuel requirements vary at varying RPM's given the same load.

 

I think Pete, Z-Ya, has a dyno that can do this right Pete? 

Edited March 5, 2010 by cygnusx1

[z-ya]

I always shoot for a consistent AFR across all RPM and load points. Theoretically it should be a flat line at the AFR that your engine makes the most power at. But there are so many variables (advance, VE, RPM, load, etc.).

 

Yes, I have Access to (wish I owned) a DynaPack. this allows you to set a fixed RPM or load band and the dyno will hold the engine at that point. We start with a generic timing table with a conservative max advance at WOT. We typically work on one RPM band at a time, and then tune each load bin. So when you are done with one load bin at a given RPM, you press the throttle a little more until you get to the next load bin. You keep repeating this until you reach your max RPM or it starts getting too hot (let it cool down and continue). Once all the load bands are tuned then we will do some max power pulls and fine tune max power by adding advance (gradually) and monitoring AFR. So add a little advance and a little fuel at the same time. You will eventually reach a point where it is either detonating, or it isn't making any more power and the AFR is getting rich.

 

My rule of thumb is 14:1 for NA and 12.5:1 for boosted.

 

So to answer your question, once you find that "sweetspot" AFR for your engine, I would shoot for a flat AFR curve in that region. Just add a little safety margin in your spark advance and AFR so you are not blowing head gaskets.

 

Pete