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?
Mine is a Riviera, where the SC was standard. The Park Avenue had an option for it (as part of the Ultra package), and I don't rememeber if there was some kind of Regal GS that might have had it (but I don't think so).
Also the Bonnevilles and Grand Prix had the same SC motor.
By the way, the Riviera is quite comfortable for such a long drive, too...
Rivieras are nice. I knew someone that had a supercharged Park Avenue I think. Very comfortable and very fast. Its amazing that its the same engine as is in my 1981 Buick Regal, and my Regal was never quick. The car will cruise on the highway at 80 MPH quite well, but a Hyundai Excel could beat me off the line from a traffic light.
I honestly have never seen an Excel reach 100,000 miles. Everyone I knew that had one had major electrical problems between 75,000 and 90,000 miles. IMHO an Excel was only marginally better than a Yugo.
In the '80s, every manufacturer had a compact hatchback with the back window angled at the same slope whose profile was indistinguishable from the Excel/Omni/Horizon/Escort/Rabbit/etc. I guess you want them all! I dislike them all.