Posted by Ben on December 08, 00 at 10:15:54:
My ex-buddy, Randy, and spent many hours under his Suburban discussing possible cause and affects of things and possible improvements to performance.
We found that engine temp affected the performance the most and could see it on his laptop that was plugged into the Sub's computer. Conclusion was that they had many "truck" attributes than "car" attributes. These are basicly the same block in both passenger/truck, different heads, etc, but there seemed to completely different behaviors at the limits (mostly thermal). Things either shut down, or switch modes (survival). One thing was that the injectors inrichened the mixture and when Randy called someone he knew at GM egineering, he was told that was to cool off the cats, as they would melt or catch something on fire. The other thing it did was switch the tranny's behavior and that there was a direct link in the program to the engine & tranny temps (there seemed to be many switch points and think Randy found & mapped them).
The conclusion was to increase the cooling capacity & reprogram the various system manging it. We knew that both the engine oil and tranny fluid needed to be kept above and also see elevated temps to boil off nasties like acid & water. A cooler thermostat (his does not have the bypass requirement that Vortec has) and install another external tranny cooler of +4 times the capacity of the stock external. Additional information on the O2 sensors and how they played with the temp/survival mode programs were being planned when my buddy started seeing a very young gal/witch (yeah, every retired, middle aged guy always seem to find these types) so I lost touch soon after and didn't get a chance to find out extactly what Randy did (he also hired a consultant to write much of the code of the reprogram in his laptop). I designed some of the new circit boards (mainly changed feedback voltage/current adjustable & porportional to original signal).
Then there is the way an engine is assembled and think some of the factory engines do luck out and get high miles per gallon, while others don't. Good old bell curve.
Comments from the collective minds out there?
-Ben