I though I would just let people know about some recent experimenting I've done.
I started a new job 70 miles from home, so I am now driving a minimum of 750 miles per week. Suffice it to say, MPG is pretty important!
Anyhow, when I started my new job my wife insisted I upgrade cars from my old Saturn. I liked my SL2 (1994), but at my new job my image is actually somewhat important (my image has to fit what they're paying me...
). So I picked up a 1998 Buick with a SC3.8. I've always liked the 3.8s because they get good MPG and can still make good power.
I was getting about 25 MPG, so I decided to see what would happen if I removed the SC belt and re-tuned. I did that, about the best I could average was about 25.5 MPG over several tanks (i.e. 3 weeks or so). I even spent a lot of time re-tuning, and maximizing the timing. Pretty small improvement at the end of the day.
The biggest difference was that I was able to run 87 octane, whereas the SC requires 93 octane. So there was some savings there. (the SC engines have a 9:1 compression, whereas the NA 3.8 engines have a 9.5:1 CR, so I was able to crank up the timing quite a bit but it still never really changed MPG).
There are a few things that I could have probably done to tweak MPG just a little bit more. One of the parameters I didn't change was the acceleration enrichment - since I took the SC belt off, the throttle movement was very different than it used to be (TPS movement controls enrichment) so the cruise control probably could have been more efficient. The other thing I could have changed, if I'd ever figured it out, was to change the characteristics of the torque converter lockup. The TC was definitely unlocked more than it should have been, but I couldn't seem to figure out how to change the lockup table.
Anyhow, I decided to put the belt back on. The difference wasn't enough for me.
Oh yeah, and did I mention that the car will run in the high 13's at 100+ MPH in the quarter mile?
-Bob C.
I dislike them all.
Linear Mode
