NewEdgeStang00

Was thinking of putting in 4.10s on an 01 Gt auto. A lot of guys have been saying they don't notice a big change in rpm or mpg, but when I calculated the gears it said at 65 mph I'm turning 2.5k, and 70 mph turning almost 2.8k. At 2k where I usually am going near 70, it drops down to 53 mph.

So what's everyone's input on the calculations? Is it accurate and did you notice a drop in mpg? I calculate my mpg every time I fill up at the pump and I get a combined 22 mpg on average.

kugzgt

theres a calculator for gears in here

http://www.paladinmicro.com/pmicro.php#

!KLeech!

just do them, 4.10's are perfect for an automatic. used to have a 2000 auto with 4.10's. you will love them, and youll honestly never notice the mpg change.

Rockwell28

Its simple math and logic you know that on the highway if your rpm's are higher that you will be burning more gas. Some ppl are up front and honest about thier loss of mpg when doing a gear change its one of the cons with the pros being quicker off the jump. Other ppl will be str8 up and let you know your highway mileage will go down by 2-4 mpg on the high end a loss of 4mpg will be 15.7 gal tank x 4mpg loss= 62.8 miles per tank lost. I went with 3.73s bc i do some 2000mile rountrips during the summer and 3.73s seemed like a happy medium to me between 4.10s and the factory 3.27s. So its clear your highway mpg will go down some ppl just deny it, others could careless and others will be honest and tell you it will go down.

Look at the math i just gave you and look at post #3 in this link http://www.moddedmustangs.com/forums...s-mileage.html

cliffyk

As Rockwell28 said, and it is refreshing to hear someone else say it, lower rear-end gears (higher numerically) will reduce your highway fuel economy. Those that say it will not either do not drive many highway miles or are being less than truthful.

Back in 2007 when I installed 3.73s I had a 55 mile, each way, commute with 40 of those miles being on I-95 between Saint Augustine and Daytona, at 75 to 85 mph. The gears cost me a solid 1.25 mpg, from a 22.75 average to 21.5--driving over the same roads at the same time of day. This was not a surprise to me, nor did I consider it to be a major influence on my budget.

110 miles/day * 5 days = 550 miles/week:

• at 22.75 mpg that's 24.18 gallons;
  
• at 21.50 mpg it is 25.58 gallons;

Some 1.41 gallons more per week. Even at today's cost for 93 octane of $3.899/gallon (just filled up my bike 30 minutes ago) that's only a whopping $5.50 per week.

Or, a couple of draft beers at a relatively cheap bar¹...

-------------------------------------------------
¹ - I like to convert life's costs into the quantity of beer they represent, it provides a much more meaningful comparison than dollars.

justinschmidt1

4.10s are perfect for the auto.

You rpms will be high on the highway, like 2800 at 70 mph.

MPG should stay around the same avg, maybe a slight drop.

MCxQubed

I think the difference in cruising rpm's between 4.10s and 3.73s is 300 rpm I think. So not much of a difference

justinschmidt1

Yea, about that...70 with 4.10s = 2800

70 with 3.73s is 2500

TRUEBLUE3934

There will be a noticeable difference in rpm between your stock 3.27 and 4.10. You are gaining 25.3% torque multiplication and 25.3% rpm increase to go with it. Take any current rpm you run now and multiply it by 1.253 to get the new rpm with 4.10 gears. That means what used to be 2200rpm will now be 2757rpm.

Your highway mpg will absolutely drop. Many variables exist so predicting the exact drop for you is impossible. However, I also saw a drop comparable to what Cliffy stated above.

All of that being said, most guys really like the 4.10s in their auto Mustang. I'm pretty certain you would fall into that category also.

Go for 4.10 and you won't be disappointed.

If you are still uncertain about such a large jump, you can go with 3.90 gears and trim back about 5% of that jump.