Tom,
Sorry, I didn't offer a good enough explanation. We are saying pretty much the same thing in some areas. Under part throttle (engine warm), the computer uses the O2 sensor to fine tune the air/fuel ratio. Under WOT, all sensors are active (except the O2 sensor) and are input to the computer. RPM, MAP signal, temp, TPS are all used to arrive at the appropriate ignition and fuel. These two items are look-up tables. If any of the inputs are changed, then the outputs will be changed. The bottom line is that you need to get the fuel correct and matched to the air being supplied to the engine and set the timing accordingly. Larger injectors can be used to supply additional fuel, but even with these, generally computer work need to be performed to get the air/fuel ratio correct at idle. Larger injectors or increased fuel pressure are needed when the air supply is significantly increased to the engine (we generally don't want to take the injectors past 85% duty cycle). There are many !
!
ways to accomplish the necessary, which is to get the fuel and ignition matched to the air.....
Frank
---------------------- Forwarded by Frank T Holloway/CA/KAIPERM on 12/12/99 08:25 PM ---------------------------
TommFern@aol.com on 12/11/99 04:00:00 PM
To: dakota-truck@buffnet.net@Internet
cc: (bcc: Frank T Holloway/CA/KAIPERM)
Subject: Re: DML: Re: Re:Best throttle bodies?-attn Frank
Frank,
I noticed your post concerning air velocity on the t-bodies. However,
woudn't going with more cubes and compression make up for the increased
diameter? I could understand losing some power at part throttle,but at WOT
isn't the PCM only going off of already established tables anyway? If one
could boost airflow with accompanying increase in fuel via regulator and
larger inj. (like I have) couldn't one tune for WOT and than have the O2
sensor adjust fuel for part throttle conditions.
This has been my whole philosophy for tuning my mods. My theory was that
the computer would decrease pulse width to adjust for part throttle with the
large injectors, but would not "see" them at WOT because of its reverting to
fuel tables. Therefore, I would go to the track, tune fuel press for best
MPH, and then let the PCM/O2 sensor do the rest on the way back home. My
air/fuel ratio meter was used to confirm the WOT runs. If I backed off on
fuel press my sensor would go lean. If I increased pressure it would return
to being rich.
No doubt PCM work would help, but I gotta tell you this motor runs so
strong right now. I question if PCM work would be very cost effective for me.
Do you think I'm leaving much behind here with the MP PCM?
Tom(11s dak)
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