Gear Question

**rbrack** · 10-05-2006, 03:55 PM

I currently have full boltons including a FAST 90/90 intake, K&N FIPK, Dynatech LT headers w/ORY and B&B triflow exhaust. I'm looking at the T-Rex cam, but before that I plan on upgrading my rear end. How do I go about choosing the gear size to go with, and what are your opinions?

**Wesman** · 10-05-2006, 04:27 PM

Do you have an automatic or a 6 speed manual?? Thats what makes the difference.

With an auto, the general rule is 3.73 gears, with a manual, most people go with 4.10's. I have 4.10's on my 6-speed, and its great

**Hurley711** · 10-05-2006, 04:29 PM

You say you plan on upgrading your rear end. By that do you mean you are getting a whole new rear?? If so than I'd go with a Ford 9 inch with 3.90 gears

**rbrack** · 10-05-2006, 05:10 PM

Any reason you like the 9" over the 12 bolt?

**Hurley711** · 10-05-2006, 05:37 PM

Originally Posted by rbrack

Any reason you like the 9" over the 12 bolt?

Rule of thumb is 9 inch for M6, 12 bolt for A4. Don't ask why, I know I've read that 1000 times. Don't know if you can get the 3.90s in a 12 bolt either, someone will correct me if you can, I know you can get em in the 9 inch.

**Red Baron** · 10-05-2006, 06:36 PM

With the 4.10, what kind of RPM's are you running at highway speed? (70-75)

**Wesman** · 10-05-2006, 07:11 PM

Originally Posted by Red Baron

With the 4.10, what kind of RPM's are you running at highway speed? (70-75)

Once again, it depends on the transmission!! Auto or stick??

With my M6, I'm turning about 2000RPM at 70MPH with 4.10's in 6th

**99RedRagtop** · 10-06-2006, 06:39 AM

Strange does have a 3.91 gearset available for 12b. and for that matter, i would use a 12 bolt thats properly built in any of these cars... when done right a 12 bolt will hold 1000hp. a descent 7 5/8 will work into the 10s with an auto and no t/brake.