Engine piston geometry change had good results.
 

I am reworking my engine again and decided to go with a more complicated style quench/reverse step piston to improve detonation resistance and it seemed to have had a nice affect on the mpg.

Went from 10.3 mpg on winter gas to about 16.7, not exactly sure if the change was only from that or from the other things that were changed but regardless the mpg is doing much better now when my foot is out of it.

Why did it need reworking "again"?

Best reason for mileage increase was better compression. Piston design could help it work with higher compression?

regards
mech

I lowered the compression about a point to be able to use more boost and also like you said I picked pistons that are very detonation resistance with a design that has a much faster and more consistent flame front.

Also tried out total seal's gapless rings to eliminate blowby (for the most part).

Mostly did the work because I wanted to refine the engine a bit more, the VVT system was working a little too well (making the cam too small down low) so I adjusted the engine so it has more TQ output below 3k.

You don't really want total seal rings.
They are not recommended for street cars due to complaints about oil burning and consumption, the manufacturer and engine shops warn again using them on the street. It has been found that the total seal rings line back up and stay aligned on most of the engines cylinders by 30,000 miles.
I looked into using them in my 489 build and went with traditional file fit rings.

Ah.....well that's not a good thing. Crap.

You wouldn't happen to have a picture of these alternative-geometry pistons?

Yeah I think I should have one around here some where, it's a reverse step dished design by icon. I'll post it up in the afternoon.

Here is a picture, it's kind of far away but you should get the general Idea. Imgur: The most awesome images on the Internet