I've put 16,000, mostly highway miles, on my 2010, auto. I always get between 27.5 and 28. That's with it loaded down for long trips, air always on and averaging 80 mph. I think the mileage is great.
I never check it for city driving, since there are too many variables and it would also depend on which city you are checking it in.
Tom

 

It did impacted me.

2011 G37x Sedan with 38K miles. 75% local.
Had Tekeda long tube in take and the ported Z1 intake manifold.
I am down from 12.8 to 10.6 with the Fast Intention RHFC on. No crazy driving.

My experience told me intake / exhaust increase mpg while suspension (coilover / brake) reduce mpg.

This is the only exception.
The car become a lot powerful and a lot more torque at 3000rpm. The gas pedal easily get there than without HFC (same pedaling get me to 3000 only get me to 2200 before).

Because the stock sedan Y pipe was so slim - found it during installation, I suspect the resonator on HFC was not enough to buffer pressure from the flow restriction at Y pipe. I have ordered a Y pipe (increase from 1.375 to 2), mid pipe is at 1.75, better than the Y pipes. This should give a gradual reduction in flow restriction, instead of having Y pipe bottlenecks in the middle.


Cats -> Y -> Mid
Before: 1.75 => 1.375 => 1.75 (dual part)
After: 2.25 => 1.375 =>1.75

With the ordered Y pipe
2.25 => 2 => 1.75

Will post back.

The could achieve 25+ when I drove a 800 mile trip 3000 miles ago - I assume good efficiency retained in drive train.

 

This is it. You are running rich. The ECU can only calculate and compensate AFR to a certain extent. When you alter your cats, you need to get a tune to correct the AFR.

 

FYI.. Last Activity for kharikrishin: 03-15-2012 10:49 PM

 

Yep...... fengyink resurrected a thread that was last active 10-11-2011.

 

Pretty useful bump as I was about to ask this haha. I've pretty much decided I'm going to get an HFC as my oem is rattling and I dont really want to go to the hassle of changing just to stay stock.

I'm looking at Fi since Berk seems to throw a CEL. Any other recommendations? Cant find any stillens since theyre discontinued.

I really hope it doesnt decrease my mpg though...

 

I have Berks and I like them. The CEL did go one but someone sent me a link to buy different sensors that would fix the CEL problem. Just havent bought them yet to try it out.

I installed them with CAI and with both it seemed to increase my mpg.

 

False!

I never use premium which IMHO is one huge myth that helps the oil companies and their shareholders.

My recent December 2550 mile round trip from NJ to Florida all on 87 octane

Four fill-ups on the trip down, two fill-ups with local short trip driving while in Florida and four fill-ups on the return



My G37S loves Loves 87 octane



Whatever mods and changes the OP made is the root cause of poor MPG

Telcoman