I switched from 87 to 92 octane a few tanks back and I have noticed a 2-4 mgp increase in gase mileage. I am going to go back to 87 again soon to see if it changes back to what it was previously. I only have 1700 miles on my car to date so I may just be breaking it in still... I am getting about 23-24 mpg average, and 28-30+ highway only.

PS all stock atm.

 

just went and visited a buddy in college was averaging 29 mpg, only mod is mufflers

 

260 mile trip interstate and state highway driving through several towns. 70-75 on the Interstate and 60-65 on the highway with a few stop and go's. This included several bathroom breaks and a lunch stop plus a few twisties at the end and I got 25.6 MPG average on the trip down here using name brand regular fuel. Mine is a completely stock 5 speed with flowmaster axle backs. Like an earlier post said your driving style is the most important factor for city driving and the shift points make a difference too.

 

I got 29.6mpg going to Fairfax Virginia from Fort Mill South Carolina on I85-I95.
I don't have the 3.55 rear end. Manual GT/CS. No mods. on BP/Amoco 87 octane gas. I was driving normally and staying about 5 over the speed limit the entire way.

 

I get about the same with my blower that I got with the CAI.

But I've never gotten above 21 mpg... ever.

 

Pleasently surprised here too. Just for the heck of it, I calc'd it yesterday. Went across the state and back 316 miles. mostly highway speeds but some country roads, and little townships too. Averaged 24.98. Starting with it toped off, and ending the same way. HESS 87 octane (w/-10% ethanol in it).