opinions sought N/A motor with F.A.S.T. and really big solid roller cam

[fear1]

I have a 363 ford with decent compression and all the good internals and a custom grind solid roller nitrous cam that i am trying to get tuned so i can just drive the thing(without the spray).
I am getting closer on the V.E. table but its such a handful on the street that it is rather difficult(drivability is pretty poor). Does anybody have a similar cam (649 lift int & ex. and the .050 duration is 268int, 276ex, lobe sep is 112 it is installed on a 108 c/l for N/A use at this time. FAST sequential with WB and ind cyl control. will i ever be able to drive this thing on the street or am i beating a dead horse here. It is in speed density mode now it idles well at 1100 rpm with 36 degrees of timing at idle. I was running it in O/L at idle for awhile but i am thinking of trying closed loop again as it seems to be loading up at idle. thanks in advance


Andy Fears

 

[Craig Smith]

You're getting to the point where getting decent idle quality and drivability in speed/density mode will be a challenge.

The accuracy of the WBO2 sensor at low engine speeds will be questionable in my mind at least. I would think that open loop would yield better results for this reason. Also, because of the lack of vacuum at idle, the ECU is going to throw more fuel at it. The lack of vacuum is perceived as a load on the engine. You can shrink the VE numbers way down to get it leaner but at that point I think the challenge will be programming a decent transition in the off-idle area. The numbers will likely have to go from quite small to much larger in a pretty tight RPM band.

You can do it though. While it was a race car only, my car was tuned in speed-density mode with my 327. Also a n/a, roller cam motor with very low engine vacuum. It started, idled, and drove around quite nicely once it was dialed in.

A VERY important thing to keep an eye on in this application is battery voltage. Do whatever it takes to keep the battery voltage up at low speeds. For me it required a 140 amp alternator. They aren't cheap but it's money well spent. Injector characteristics at small pulsewidths are heavily influenced by fluctuations in battery voltage.

Let us know how you do.

 

[fear1]

Thanks for the reply Craig. As you have said my V.E. numbers ramp up very quickly, at idle i have like a 44 and the MAP shows about 82. as soon as i get on the throttle there is a pretty big hesitation and i am not sure if it is a lean stumble or not. I have tried messing with the A.E. vs. TPS rate of change to try to give it a shot of fuel when i tip in to it and i have the table giving it 2.12ms across the board. It helped some but still has a pretty bad transition. once it gets to about 3000 rpm it pulls clean and strong as long as i can stay in it. if you might have some more ideas i could e-mail you my gct and maybe a datalog file. I have a 130 amp alternator on the car and the voltage stays pretty steady. i have been idling it in O/L for awhile and have the closed loop high at 1400 and the closed loop low at 1300.

thanks again
Andy Fears