After changing from 3.31 gears to 4.10 gears in my 2010 GT I am getting what I consider terrible mileage. It seems to average out at around 11.3mpg. What is weird is that when I look at the average MPG, it goes down when I'm sitting at a light idling. Does that make any sense? I would then idling at around 900rpm would keep the average steady or make it increase considering that its not running at 2,000-3,000 rpm as compared to driving.

Am I just expecting too much out of the car mileage wise? I try to drive it conservatily by rarely launching from stop and shifting into high gears earlier. Am I doing something wrong?

 

You should expect the mileage drop after going from 3.31 to 4.10s. Some one correct me if i'm wrong but I believe you are thinking about the calculated average MPG wrong, it will be highest if you shifted to neutral while on the highway because you would be getting many miles off of a low engine RPM. If you watch the average while stopped you would effectively get 0.0 mpg because you are not moving and thus bring the average down.

Personally I only average 12-14 mpg with strictly city driving and 22-23 on the highway but I have a bit of a lead foot.

 

your gas mileage when stopped should not be 11.3. It should be 0.0 as mentioned because you aren't moving. Now, if you're AVERAGING 11.3 for city driving, then yes, that is pretty bad. Have you recalibrated your speedo? I don't see how that would matter, but it could have something to do with it. Idk. I went from 23mpg with 3.55s, intake and a tune to 22.3 mpg with cams, LTs, intake/exhaust, tune and 4.10s...no clue why yours is so bad.

 

4.10s should not cause a huge drop (in the old days it would, but not any more). Maybe 1 to 2 max. What was your mpg before?

Also, I notice lower MPG after I load a tune and after about a week it gets back to normal. Maybe you should just give it a week and see if it changes.

 

Did you adjust for 4.10's in the tune? If not your measured distance will be off.

 

Yeah of course the tune is all correct. Using a tillman 93 all out tune. Maybe the tune could also affect the gas usage?

 

I got 17-20 mpg in town and mid-20's on the highway when I had 4.10's (Mileage divided by gallons). Take off in 2nd and short shift. Change gears as soon as it will pull the next gear cleanly. You should be shifting into OD at 30-35 mph for best mpg with 4.10.

 

First, verify that your speedometer has been recalibrated with the tune by a GPS comparison. As stated earlier, if the PCM hasn't been corrected for the gears, all of your on-board fuel estimates will be way off.

Also as stated, your on-board is an AVERAGE and not a real-time value. And considering the inaccuracies of the on-board computer, you should begin hand calculating your fuel mileage once you verify that the speedometer/ odometer are within tolerance. +1 on fuel mileage being 0, real-time, when sitting and idling, thus causing your AVERAGE MPG's to drop. Duhhhhh.

 

Overall normal driving should be very little difference..!!!

 

I guzzle gas, but then I drive a Mustang and it's a GT. I don't know why your fuel mileage is that bad, but I have been hand calculating mine. I run 4.10's and my drop has been very minimal. It still lingers around 18 - 18.5 mixed driving, the onboard computer is close. Maybe your tune is too aggressive and running too rich causing you to guzzle even more gas. Do you have other mods?

BTW, 4.10's are for launching, not for top speed, have some fun with it. I have an auto and 1-3 gear is virtually non-existent. Are you sure you're driving your 4.10's right?