I don't see how this would help. Under cruse the computer is in closed loop and maintaining 14.7-1 a/f ratio. you should be able to adjust your timing and shift points under light throttle to what you think will get you the best mileage and when you get into it harder adjust them to what you think will give you the best performance. not really any need for 2 pcm's.

i am not sure if there is any way to run it lean under cruse with the stock computer. with the megasquirt and a wideband i can command any a/f ratio anytime i want. there i a a/f chart you can fill out for different throttle positions and loads. under light load i command 15.5-1 1/f ratio. i think going that lean does increase emissions some how. i got 12mpg with my 408 on drag week towing a trailer so I am pretty happy about that.

I think the best thing you can do for mileage is drive like an old man.

 

just for reference. i just filled my truck. computer said 12.1, hand calculations...13.5. but fuel used was DEAD on

 

Thanks, Did not know that.
Mark

 

The other best way to get optimum mpg with FI is with 2 bar map tunning and having it nailed down. Getting it just right would take some time but be worth it. That way you can custom tailor your fuel at lower rpms and boost levels during moderate acceleration. Basically you don't need 11:1 afr at 2500rpms and 2lbs boost. I even had mine tuned with 1 bar map with just rpms. at the lower rpms 1800-3000 when I would get tip in boost from that 3.0 pulley on my 4.8 radix I was seeing 10:1 afr or worse. We (Gomer and I), backed the fuel down while in PE (under boost) to around 12.5 or so, just enough to stay out of KR. This kept my bumper from turning black at least. That was the poor man's way of doing it. I have the new HPT pro edition that I will be using 2 bar map to tune it the right way this time.

 

???? Fuel used was dead on and yet your mpg calc didn't match the computer. How did you use a different mileage figure than the computer? - that's where you get the value from, in the first place.

 

hey man dont ask me. i just report what i see. the dash readout on mine has never been right ever since i bought the truck. thats why i hand calculate. the only thing that has ever been close, is the fuel used