Not sure how much this will matter to others but I thought some might be interested. I have an 1988 C4 35th Anniversary Edition car with 105K miles on it. Mods are as follows:

1. 2.5" dual pipes with no cats and magnaflow system.
2. Screens removed from MAF.
3. Throttle body bypass.
4. Air system and pipes completely removed.
5. 180 degree t-stat.
6. Aluminum 3 core rad.

Otherwise the following OEM style work has been done:

1. New plugs (platinum's)
2. New Oxy sensor.
3. New wires
4. New filters all around changed yearly regardless of miles (Fuel, Trans, Air).
5. New fluid all around changed yearly regardless of miles except oil which is changed every 3 months along with the oil filter every other change.
6. Brakes and suspension have been completely rebuilt.

I started out for my Thanksgiving day travels very early in the AM here in the NE USA. Air temps ranged from 48 to 51 degrees. The tank was completely full. I traveled 83.7 miles all highway with the cruise on 90%of the time at 65 MPH with an estimated MPH average of 60 +/- 2 miles per hour. The digital read out on the dash read 22.4 MPG at the end of the 83.7 miles. When I re-filled the tank and calculated the actual amount used I came to 22.8 MPG so the dash was very close and I feel I am getting pretty good MPG considering the estimated MPG from the time of sale when new for HWY miles is 22 MPG. Oct 93 was used. Once I filled up I then continued for 63.6 miles on back country roads at an average MPH of 45 +/- 2 MPH with no cruise control used and I got 23.5 MPG from the digital gauge on the dash. Next will be a city test but that is a bit harder since I have no plans to do 80 + miles of city driving and in general I avoid city driving as much as possible.

The injectors are all original with 105K on them.

Thought a few of you guys might enjoy the notes from the test.

 

Real world quantifiable test results are always welcome as a benchmark for performance upgrades!

 

Thinking further on this I will likely do the next test over the same path in about a week or so with 89 Octane fuel and see if I get the same results or if it will be better or worse on MPG.

 

If you really want to be analytical about how you track your data, try using this site...

http://www.fuelly.com/driver/tom400cfi

This link is to my 'garage', but try it out!

 

Ok I just did 69.2 miles with a full tank of 89 octane and came to 24.34 MPG. I ran the same general way I ran the first test outlined in the opening post of the thread. Only difference is the octane of gas and the outside temp which was 38 degree's. I am going to check it again next week as I find it hard to think I got 2 extra MPG just by changing the octane. Ill keep u posted.