Just installed Perrin resonated exhaust and noticed an increase in MPG
 

Installed a TRD intake and Perrin resonated exhaust and noticed an increase MPG from 30 to 36 MPG. Is this normal due to less restrictive air flow. BTW I love the sound just enough rumble without annoying drone.

No. It isn't normal for it to do that. Everyone would do them if that were the case. Maybe a 1-2 mpg difference but not that high.

Exhaust is louder so you don't have to drive it as hard to get the sound?

I'm jelly of you all and your 30+ mpg... Every time I get in the BRZ the inner madman comes out and mileage goes bye bye~

Generally speaking, if you removed the cats or got high flow cats, you would probably see a MPG increase. Even then it won't be much, maybe 2 or 3 mpg greater than before cats today are pretty good.

Basically, I have no idea how your MPGs increased. Also do you have an auto? Cause those numbers seem really high for the manual. I struggle to get 24. . .

+1.

On a cruise to California (800+ miles each way) I took one whole tank in 'eco' mode, if you will, and managed a whopping 35 MPG. Then I did the rest of i5 at 120-140 MPH and got 18MPG.

Going to the coast over hills, the computer claimed 41 MPG. I believe it too, stuck behind traffic, 55 MPH, coasting a long ways.

http://i.imgur.com/5aEWOt5.jpg Like a moron, I didn't include the fuel gauge in this picture, but this was about 60-65 miles into the drive

It's an automatic, that explains it and the lower highway speed too. Going 70 on the interstate, I top out at 34 mpg roughly with my tires/wheels/suspension in a 6 speed. I'm at 3100 rpm @ 70 mph which to me seems kind of high. 2300-2500 would be much better on gas mileage.

The auto has a much better cruise gear and ratios for daily commuting.

This^...and FWIW, when I manually calculate my mileage at fill-up, it's typically 3-4 mpg LESS than the trip computer is calculating.

Mines only been .8-1.5 less than the comp so I don't even bother hand calculating anymore. Pretty much just let it go or shoot for 280 miles before my fuel light comes on.

Yeah, mine is usually off by 3-4 as well even driving like a grandma for a tank. Lately since I got my exhaust fully finished, my MPG has dropped to like 25-26 for obvious reasons.
:burnrubber:

*cough* BS *cough*

Honestly, if you guys really want accurate MPG readings, use Fuelly and base it off your Odometer. Its as accurate as possible within +/-.1 or so. (Pending human error)

I have the TRD Intake and a Perrin Non resonated catback. I noticed no huge gain in my MPG. Actually I noticed more of a gain after I stopped buying grocery store gas.

My MPG (average of last 3 tanks):
Digital readout: 30.6
Hand Calulated: 28.6
Mileage Android App: 28.8

I'd say my digital readout is consistently 2 MPG high.