Yes you will be at higher rpm at all times and about 2-3 mpg average loss. You will be visiting the gas station much more often with 4.10's. I can literally watch the dial move down now lol.

How are people getting 22-23 mpg gas mileage? I never get above 19 and now with the 4.10's I average 17 mpg.

 

If you're on a budget and drive 85 miles a day I would say don't get the gears. However if you've got cash to burn then definitely get them because they're fun as sh%%.

 

Don, are you sure your tach is ready correctly???? I would be tickled to get your gas mileage with the STOCK GEARS. I am also running in the 2200 rpm range with the stock auto gearing @ 70 mph. I am not sure how you can only be running 2500 rpm @ 70 mph with the 4:10's. One of the ways I know I am getting above the 2000 rpm mark is that my Borla's stop the drone at 2100 rpm and that is @ 70mph and above.
Scott

 

Take a look at the attached spreadsheet. It is set-up for the stock tire diameter right now (27.18"). My 275/50-17s are about 27.8" tall. Plug 27.8 into cell J3 to see what it is for my car.

 

If i go with 4:10s do i need to reprogram?

 

I have seen this chart before. I can only tell you what my car does with the stock gears. I want to go with the 4:10's but this is my every day car. Gas mileage is important!! I want the extra performance of the 4:10's but am not willing to give up 2/3 MPG. I see the chart but I still have stock gearing and my gas mileage is not like yours. I know what my tach reads and it must not agree with yours. If I am running 2100/2200 rpm @ 70 mph. I will run 2500 @ 75 with the stock gearing. Not trying to be an ASSwitpe but Ford only claims 18 /23 mpg for the GT with stock gearing so how in the world do you get better with the 4:10's??? Just doesn't make sense!!!!!
Scott

 

Im in the same dillema 3.73 and 4.10 what are the rpm's at 80? maybe some of you auto guys can take a quick cruise and find out for me, also how much am i looking to shave off my 1/4 mile with these?

 

Look at the spreadsheet I posted above.

 

I think the 4:10's will get you close to .5 sec. off your 1/4 mile speeds. Not sure about your RPM @ 80 MPH. My guess is 2800 to 2900 rpm.. Based on what my car does with stock gears.
Scott

 

Well you need to recalibrate the speedometer. So if you don't already have a tuner...you will need one. I used a Predator to recalibrate and kept my 93 octane tune.

I will say that my engine light has been on since installation of the gears...i'm thinking I need a custom tune now.

 

my car with stock tires turns about 2100 rpm at 60 mph.at 80 i think its about 2600 rpm at 80.this is with 3.73 gears.

 

What would 20" rims do with changing gears????? Anything??