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I had a some time last night so I programmed a few modified EPROMs
with tweeked code for the MAC-11B ECU. First off many thanks to
Scott M., Orin E., David K., RDH and QSHIPQ for help along the way.
Science project: 83 ur-q with 89 200 MC engine installed, single knock
sensor, stock wastegate spring, slightly tweeked stock K26, MAC-11C
ECU with MAC-11B code, ur-q downpipe, etc.
As many are aware Scott M. and Orin pioneered the chip only 1.8-2.0
bar boost modification for the single and dual knock sensor engines.
Stiffer wastegate springs aren't needed here, the ECU software is modified
so that the maximum boost pressure setting is raised using the stock
wastegate frequency valve. With this mod, all factory safguards are intact
Starting with info from the "ECU crew", I modified my software to get
this increased boost level. Since I live at 5300 ft above sea level in CO,
and with info from a very informative PDQSHIP post, "Rocky Mt. Boost",
I realized that more is not always better. I designed a boost profile, based
on the altitude my car will be driven at (remember that pressure ratio), while
trying to stay in the high efficiency region of the K26 compressor map.
I created 2 versions of the code. The first raised the boost pressure to
a max of ~1.8 bar. The second used the 1.8 bar boost pressure, but I also
twiddled with the boost curve lookup into the timing table. Playing with the
timing table maps are equivalent to what the hardware hacks on the boost
pressure sensor voltage signal are doing. The result is..., #2 is a keeper.
Getting that timing advance really helps the engine spool up faster. I was
I was conservative in the timing map change as I only changed the index above
1.0 bar and didn't advance it as much as some hardware mods do. On the
uncalibrated VDO boost gauge, I was seeing about 12-13 psi boost with a +/-
2psi delta around that point. If you sneak up to 12 psi, the ECU held it pretty
steady. But if you ramped up quickly, it would overshoot to 15 psi and you
could really feel the WGFV trying to do it's thing. That control loop is pretty
underdamped with a number of back and forth swings.
Next up, I will keep twiddling with the boost index into the timing map. There is
"more power" lurking in there. I will also install my 1.8 bar WG spring as the
preload will really help the boost ramp up quickly and then used the WGFV
to hold the desired boost level.