You need to advance your timing while in cruise.
Install an MSD 6A box & also use the MSD adjustable timing knob to advance the timing while cruiseing.
The poweglide IMO is not as good on mileage as a TH350, I would swap out that trans, for better mileage & FOR SURE better accelleration.
You would need a short tailshaft TH350 & it's a direct swap.

You could have kept the V-8, but you will not get the looks or the people asking you about your ride.

If the engine is a bit run down, your mileage will suffer also,what camshaft are you running?


MBHD

 Originally Posted By: Overbiter
I am looking for an answer to this question about MPG as Well, My 65 Chevelle has a bit of a run down 250 in it, and I seem to be getting about 16 mpg highway miles at 50 MPH. I have a stock internal 250 with offenhauser 4 intake,with a Holley economaster 2 barrel, I think they're 350 cfm. Hei,Powerglide car, with 3.08s weighs 2900. What am I doin wrong? 16 Mph I coulda kept the 8.

So 16 MPG is My number anybody else wanna put up theirs?

12 port SDS EFI