what rear gears for a twin screw 5-speed 4.6

[russ1979]

so the rear end on my wife 04 is leaking bad. i think it is just from the seal but i'm thinking as long as we are going to have the cover off anyway this may be a good time to swap out the rear gears.
but what size????
4.10's are out as it does do a far amount of hwy travel and we want to keep the car mild.
we want to do headers, high flow x with cats, cat back and a Kennie bell but thats about it.

so sould i stick with the 3.08 move to 3.55 or 3.73's?

 

[ItsStock02]

3.73s

 

[Maxpowers]

4.10's or bust.

So many threads about this my head's starting to hurt.

 

[wmburns]

Use 3.73 gears for supercharger 1/4 mile

+1 for the 3.73's is best for 1/4 mile. But this is not IMO.

Check out the following from the KB site (page 7 under "gears")

http://www.kennebell.net/techinfo/ford-techinfo/46gtTechTips.pdf

OBTW, I think the stock gears for the 04 GT is 3.27.

 

[trinity_gt]

If it's leaking from the pinion seal the rear cover doesn't have to come off to replace it. You can:

• measure the pinion preload before removing the pinion nut
• remove the nut and the driveshaft flange
• pop the old seal out and put the new one in
• re-install the pinion nut and tighten it until the pinion pre-load matches the pre-disassembly torque

If you over-tighten the nut you'll have to take the rear apart to replace the crush sleeve.

As for gear ratios, I've got 3.73s in my KB 2V and am pretty happy with them. Honestly, the car is torquey enough down low now that 3.55s or even stock 3.27s would work fine too. 3.73s really make the car a handful -- and fun -- in the lower gears with 245 tires though...

 

['03GTinFLA]

Funny how guys who say 4.10 don't have twin screws, cause you better have sticky tires and be able to drive or else you'll just smoke em up and go nowhere, which can be fun. I have a 1.7 KB and had 3:73's and 1st and most of 2nd were all spin with BFG KDW2's 275's. I have 3:55's now that I swapped to an IRS and I like that much better. I don't take it to the track, just street fun, and those work well for me. I think I wouldn't mind 3:27's either.

 

[usaf_branham]

I have 4.10's... too much gear, 3.73 would be ideal / eventually i will swap it

 

[trinity_gt]

I agree with the previous two posts, at least in spirit. While I have "only" 3.73s this is as much gear as I would want. The whole idea of very short gearing is to make up for the inherent low-RPM torque deficit from which the 4.6 suffers. A PD blower erases this deficit by effectively giving big-block torque numbers.

There's no need for so much multiplication in the rear end when the engine is now making decent torque under the hood

 

[sneaky98gt]

Funny how guys who say 4.10 don't have twin screws, cause you better have sticky tires and be able to drive or else you'll just smoke em up and go nowhere, which can be fun. I have a 1.7 KB and had 3:73's and 1st and most of 2nd were all spin with BFG KDW2's 275's. I have 3:55's now that I swapped to an IRS and I like that much better. I don't take it to the track, just street fun, and those work well for me. I think I wouldn't mind 3:27's either.

Yup. I have a PD blower, but with the NPI heads and only 6ish pounds of boost, I'm at about 50 less foot-pounds of torque than the KB PI guys. My car with the stock 3.27s is still plenty fun. It'll get the 255 Nittos smoking pretty easily in 1st, especially if I just smack it. It's not quite enough gear for track use because I can't really get it out of the hole all that quickly, but that's due to the stock 4R70W more than anything. It hooks fine with 275 drag radials, but just won't pull any faster than a 1.9 60. My car as it currently sits (325 rwhp, 335 rwtq) with a 5-speed would be hella fun.

Honestly, making 400ish foot-pounds of torque at 2500 rpm , I would go no higher than 3.73s with my auto. With a 5 speed, heck, I think the stock 3.27s would be fine for a very fun car. 3.73s I would think would be a lot on the street, but for track use on a 5 speed, I imagine 3.73s on a 28 inch tire would probably work nicely. For all around fun and street/strip use, I personally would go with 3.55s. Enough gear to smoke em if you want to on the street, but not so much that it's impossible to get traction at the track.

I agree with the previous two posts, at least in spirit. While I have "only" 3.73s this is as much gear as I would want. The whole idea of very short gearing is to make up for the inherent low-RPM torque deficit from which the 4.6 suffers. A PD blower erases this deficit by effectively giving big-block torque numbers.

There's no need for so much multiplication in the rear end when the engine is now making decent torque under the hood

Another great tech post.

 

[Dark04GT]

The consensus seems that 3.73's are your max.

With a KB I say rebuild what you got, get a good seal, good gear oil and call it a day. The stock 3.27's work fine with your power levels / more gear will just make for potential traction problems. If the car's primary purpose is "mild driving" then keep what you have, no reason to set it up for the 1/4 mile if the car spends the majority of the time on the hwy.

 

[russ1979]

to say the car spends the majority of the time on the hwy would be a streach but this is my wife's mustang (not her dd) yes she is a car girl but she is new to a v-8 power and stick shifts. thats why we want to keep it mild. just a fun weekend toy thats qiuck.

i'm thinking i will just fix the leak