FW: MAF Upgrad

[Joe Boucher]

Over the years, long before I found this learned group, I have struggled to
think of a way to use the stock FI MAP or MAF setup on a higher performance
engine.  The trick I'm centering on now is keeping the flow signal from the MAF
to the ECU within the range of the one byte (0 to 255?) setup in the GM ECU
code.

So, for a max digital signal of 255, the air mass flow through the MAF will
equal a certain amount.  Someone posted a few days ago, this value for a MAF
for a 350 CID will equal about 325 HP.  If I wanted to flow more air to the
engine and stay within the 255 value, I could route a tube around the MAF or
mount the MAF in bigger tube and let the additional air flow around the MAF.
For wide open throttle, size the tube correctly, use larger injectors and bingo
you have the correct air fuel ratio.  As Mr Pelban said in other words
recently, it's not immoral to lie to a ECU.

It's the situations other than WOT that I can't figure out.

First idle.  If the previously mentioned stock 350 MAF signal to the ecu is 1
for idle, this idea is in trouble.  The idle fuel requirements for a pumped 350
aren't going to be much different from the stock situation.  So now with the
bypass, you have more flow going in with bigger injectors and the ecm will be
receiving a smaller signal.  Bigger injectors, smaller signal.  Maybe this
isn't a problem.

Second, the nonlinearity of compressible flow.  My grasp of compressible flow
is so weak, that I haven't figured out if the percentage of flow through the
MAF and the bypass would remain resonably equal over the range of flows from
idle to part throttle cruise to WOT.  Would the Block Learn and the closed loop
situations handle any changes in flow percentage through the bypass and MAF?

Any thoughts?

Joe Boucher
'70 RS/SS Camaro  '81 TBI Suburban

Frederic Breitwieser wrote:

> >Just had a better idea - use an ECU designed for an engine half the
> >size/output, and add extra drivers do run the other ser of injectors.
> >There is always more than one way to skin a cat - the first step is
> >always the same - you have to catch the cat!!
>
> I was thinking of using the stock ECM, doubling the injectors per cyl and
> doubling the airflow, retaining the 14.7:1 a/f ratio (obviously, the math
> is more complex than that, but it illustrates the idea).  I want the ECM to
> think its running on a one inj per cyl system, without additional boost,
> and to use the O2 sensor to compensate.
>
> We must have different cats - all three of mine walk over to my lap and
> sit.  Even the 24lb tomcat :)
>
> Frederic Breitwieser
> Bridgeport, CT 06606
> http://www.xephic.dynip.com/
>
> 1993 Supercharged Lincoln Continental
> 1989 4-Door Softtop Humvee (Hummer)
> 2000 Buick GTP (Mid-engine track car)
>
> ---