DFI, Batch Fire, and other myths

[Chris Conlon]

Hi again,

At 08:46 PM 1/21/99 -0600, Tom Sharpe wrote:

>Boy I started something.   I want to add IMHO that vaporization helps
>economy/efficiency under cruse conditions but decreases effective intake
>charge at WOT. Atomization helps cruse and WOT  conditions as well as not
>hindering WOT.    Tom

Ok, first I agree with all of this. Designing for big WOT power, *and*
for low BSFC at cruise is not the easiest combination in the world.

One thing that might work would be to have a 2 or 4 injector TBI setup,
with those injectors sized to get you up to maybe 25% of max power,
and relatively huge TPI injectors in each port. This way you can have
really big TPI injectors without worrying about idle quality. And, as
an added bonus, you probably will get a higher % of the fuel from the
TBI injectors to evaporate, which is probably a *good* thing for BSFC
at cruise. (Actually I don't know how the pumping work vs. compression
work numbers pan out... Greg?)


As for resolution of various ECU subsystems, this is a subject near
and dear to my heart. So I'll try to keep it short from boring y'all!
(Plus I don't have hard numbers to show, yet.)

Bruce wrote:

>But, but, what about the filtering?.  Doesn't that fly in the  face
>of needing absolutely accurate MAP sensing?.
> **Notice the question mark, I'm asking.
>  This "filtering" is a funny animal, in so far as using larger ID/
>loner sensor lines can make a vast difference on some
>applications, and I've always had better response with smaller
>shorter lines.

MAP filtering is an important issue IMHO, and I'm curious how OEs
handle it. The MAP signal spectrum has strong components based on
the RPM, which can vary over a 10:1 range, and components based on
the fixed lengths of intake elements. (And variable intakes, in
some cars.) As far as I'm concerned you need dynamic filtering,
which changes with RPM, if you want good throttle response over
a wide range. (The possible exception being a good accelerator
pump algorithm, which would essentially use the TPS to fill in
the data you miss by over-filtering the MAP signal.)

As far as the whole turndown ratio issue, are OE apps using a
regulated injector drive voltage (or current-sensing drive
circuits, better still), or is there still a low-battery injector
pulse width correction? (As with some really old stuff.) One more
good reason to go to peak and hold, IMHO, is that you can use a
5-6v regulated supply, which should be doable under almost all
battery conditions, and current-sense drivers which automatically
compensate for the change in injector resistance with temperature.
If you're trying to get accurate, short pulses from big injectors,
you need all the hardware assist you can get. (Note this mainly
applies to boosted engines which have a wider dynamic power range.
But boosted engines are mostly what interest me.)

...

Someone asked a bit ago about low-pressure sensors. I'm gonna come
off sounding like a damn Motorola ad here, but I really like their
pressure sensors. They have a couple designed specifically as MAP
sensors, and some others in lower and higher pressure ranges. The
ones I use are mostly temperature-compensated, and have a
conditioned 0-5v output. The bandwidth is reasonably high, though
you can get better accuracy if you filter it down some. (They don't
spec it as -3dB bandwidth, they spec it as 1msec response time from
10%-90% given a full-scale pressure pulse. I'm too tired to do the
math but think 500Hz or more.) Accuracy is conservatively spec'ed
at ~1%-1.5%, you can do better if you're willing to limit the
temperature extremes, filter down to lower bandwith, and do some
math on the output signal. (Also the lower pressure range units
have more error.) Not instrument-grade but damn good. More
importantly short term drift is low. Best of all they're cheap,
the last set of 2.5 bar absolute units I got were ~$16 each in
onesies. Anyways sorry for sounding like a damn ad, I don't get
a kickback, honest! I just like the damn things.

http://mot-sps.com/senseon/pressure.html


   Whew, ok, hope this interests someone.
   Chris C.