my friend has a question

[Skyler1991]

He has a 2007 v6 mustang manual trans and was wondering if he should change the gear ratio to 3.75 or 4.1?

[sonicpony03]

I would say 3.73's would be the best for his mustang.
I've heard that 4.10's can be too tall for the manuals, and gas mileage is slightly affected if one does a lot of highway miles due to the increase in rpms that the car is running at.

The common rule is 3.73's for manuals, and 4.10's for autos.
But I think it depends on the driver, the driving situation (racing, daily driver, etc.), and the car itself (how it is tuned and set to perform)

I think the stock one's come with 3.27's, so he would definitely feel the difference with3.73's. 3.55's and 3.90's are another option if he want's less or right between the other two, but from what I've heard 3.73's are the common ratio for manuals.

Basically, it depends on what he wants from the car. If he wants better acceleration and a more torque-like feel, 3.73's are his best bet. Just make sure to have a tlok installed when doing the gears, this will give positive traction to both wheels which will make for better launches and two wheel burnouts.

If he plans on adding a power adder in the future, I would consider an 8.8inch rearend from a GT. Newtakeoff has the unit with the taller gears already installed. Or you could pick up a used one and get a rebuild kit.

[Skyler1991]

Thanks a lot man! Thats exactly what he wanted to know.

[sonicpony03]

No problem man. Upgrading gears and a tlok is the best thing your friend can do to improve his mustang. It can be costly, usually anywhere from 500-1000 dollars for install and parts, but it is definitely worth it.

There are two important things regarding the install.

1. Make sure the shop is reputable, trustworthy, and will do the install correct the first time, because it will cost even more to have it redone again.

Here is a quote from the almighty SpectorV here on the forum:

"dont skimp on this install as doing it wrong can cost you much more than just a redo as once the gears get worn wrong.. you have to buy new ones.

Basically if the shop tells you when they install them they set the backlash, pinion crush sleeve, gear wear pattern and the likes then they know what they are doing, you dont just bolt them up and go.

Get a warranty (here is the tricky part for some) IN WRITING stating that you are covered for X miles from whine or breakage or any other issues. If one of the little bolts around the ring gear comes off say bye bye to the entire rear end."

2. A tuner is needed to adjust for the taller gears. It will correct the speedometer after the install. He can either buy one, which can be used to boost hp/gas mileage, raise rev limiters, etc., or have the shop tune it if they do so.

[jimbullit]

Changing the ring and pinon is a time intensive upgrade-when done properly. The technician/shop-needs to have all of the tools and skill-as they have to be able to "install/uninstall" the gears-until all of the adjusting is correct-especially the run out. Most technicians do not know how to do this properly-as all of the adjustment(s) are "old school"-and they have never done it.

[2007STANG]

How to install your own gears!!! - Mustang Forums at StangNet here is a post on installing gears but alot of critical steps are not mentioned like setting the gaers