View Full Version : Buick Turbo 3.0 2-bar MAP tuning progress

01-13-2008, 05:29 PM
Okay I'm trying something halfway crazy but I have one main reason. I want
to use what I have on-hand and try to make this work. I know it would be
easier to get a different ECM, but I had this whole system on hand already.
I've been posting about my Buick tubo 3.0 engine, with draw-through TBI
system. I have it running, and it is doing pretty well! First I got the
engine running with a normal 1-bar MAP sensor, and roughed-in the idling and
off-idle response. Then I installed a 2-bar MAP sensor. Since the sensor
voltage is now "halved" for any given MAP pressure, I scaled all the
MAP-based variables accordingly. The BPW was increased alot but not exactly
doubled. I had to "play with" it to get it running right. The delta-MAP
enrichment was scaled by 2. The VE table values from 0 to 50 Kpa were
filled with the contents of from the original table from the corresponding
cells that were 2 x the MAP. In other words, new table "10" value came from
original table "20" value, new table "20" value came from original table
"40" value, etc. From 50 to 100 KPA I filled the table with the "100" value
from the original table.
For the main spark table I "borrowed" the spark table from a 4.3 Syclone
truck calibration, copying the values from the Syclone table into the
positions in my "new" table appearing at 1/2 the MAP.
Did all this nonsense work? YES it does. The engine started and ran
fine. No SES light or other malfunctions. With some minor tweaking of the
timing, BPW, and delta TPS enrich, the engine starts warm (but still needs
work on cold-starts), idles smooth, and off-idle acceleration is perfect.
There are NO drivability issues whatsoever.
The high MAP VE table will be tuned tuned with wideband for safety. At
the moment I'm getting a set of safe tires for this car and then I can do
some "real" tuning. When the datalogger is connected and I can log AFR and
Knock I will feel more confident to really let it rip.
Recap of parts used:
1990 Chevy Truck 1227747 ECM / modified 4.3V6 calibration.
1991 Pontiac Sunburd Turbo 2-bar MAP sensor
1990 Chevy 305 truck TBI and injectors
1979 Buick Riviera turbo and manifold
1984 Century 3.0L engine

01-14-2008, 04:08 AM
I worked some more on my Car of Many Colors with the
drawthrough turbo TBI engine today. Got the 2-bar MAP installed and did some
rough tuning with wideband datalogger. This was the first time it has made
any BOOST, which it did completely silent. I didn't think the turbo was
working until I looked at the gauge. It is silent. I'm accustomed to the
inlet sound from the turbo on my other car. This draw-through is quiet. I
only let it get to 5 PSI due to audible detonation but this is expected
since no real tuning has been done.

The AFR stayed around 12 under boost (good IMHO) but the timing needs
work. The spark map I copied from an intercooled engine calibration and
this one is hot-air. Any word-of-thumb rule on degrees of timing removed
per pound of boost?

The drivability tuning was easy. I was able to give it much more off-idle
pep by advancing the spark in this region. There is plenty of room for the
large pump-shot needed with the big plenum and turbo manifold under the TBI.

Next weekend it will be tweaking of timing in the above 100 kPa region.

By the way - looks like the oil return angle is safe. At first I thought
there was a major problem but then remembered one fact... The car had been
out of service for years so all sorts of crap had to burn out of the muffler
pipe. After that, there was no objectionable smoke or oil leakage. It will
get a new 2.5" exhaust anyway before I do any serious high-boost tuning.

So far so good!