8.8 Rear gear swap

[erratic50]

It's time. I have an SN95 rearend from a 95 with 2.73's in it under my car. I love the brakes but I hate the extra width under a foxbody.

I am going back to my old Foxbody 8.8 as soon as I am done building it into what I want. I bought Moser axles and everything to rebuild it including a crush sleeve eliminator, carbon fiber clutch pack rebuild, etc.

I'm planning to use spacers to get the track width out back exactly where I want it compared to the front.

I am down to the very last decision - gears. I've done the ratio math 15 different ways and know exactly what each one will give me. My delema is a 3.73:1 is going to be too high and a 4.10 seems like it will be too low.

I run a T5Z and if I have to bang 5th in the 1/4 mile it's a 37% drop in RPM because of the 0.63:1 overdrive which will not work. Ouch. 5th must be avoided!

There are only a few companies that offer a 3.90 gear set and Ford is not one of them. If you read as many forums as I do you'll see noise complaints are a constant for every other gear manufacturer that offers gears for an 8.8 other than OE ford and Ford Racing gears before Motive started making them. (M in part number) So it's a roll of the dice.

I can either live with being on the rev limiter in 4th with 4.11's or gamble on noise from a 3.90.

I read somewhere that US Gear makes the OE gears for Ford and made the good ones from FRPP. Not sure about that though.

Ive never heard of anyone with motive gears that doesn't have noise. Richmond is even worse usually. I'm thinking of trying a US Gear 3.90:1 ring and pinion. Looking for experiences from others.

Rear diff noise would seriously torque me off.

[quickshift]

4.10s and a taller tire.

[Foxy 83.5]

4.10's and don't look back.

[Haystack]

Exactly, if ya can stance and space out the car right, a 28" tire should fit pretty good.

I ran 275/60r15's on my old tbird. With a .68 5th gear t-5, i dropped a couple hundred rpm's freeway speeds. With the 2.73 rear i already had, it dropped me down to the equivalent of a .62 od ratio, which is right about where i wanted it. My first long drive with it, i got a bit over 30mpg, but the speedo didnt work and that was based of google maps mileage minus half a days run around town before the trip.

Once i got used to banging gears and spinning through 1st, my mpg's dropped down to less then 25. Every time i passed someone id drop it down to 2nd or 3rd and blow past em. It was a really, really fun car till it started eating motor mounts.

[erratic50]

It's all games and fun until something gets hurt..... then it's just fun?

Lol.

Yea, good feedback gang.

Good point on throwing taller tire under it to make up a ratio if I don't like 4.10's.

with a 245/45/17 tire the car currently runs 60 just under the rev limiter in 1st. Way too fast for low....

so e of the quick ratio math I've been looking at:

Original WC T5
3.35 * 2.73 = 9.1455
0.68 * 2.73 = 1.8564

Current: T5Z
2.95 * 2.73 = 8.0535
0.63 * 2.73 = 1.7199

T5Z with different gears

3.90's:
2.95 * 3.90 = 11.505
0.63 * 3.90 = 2.457
future Viper spec T56 0.5 * 3.90 = 1.95

4.10's:
2.95 * 4.10 = 12.095
0.63 * 4.10 = 2.583
future Viper spec T56 0.5 * 4.10 = 2.05


Granted 12:1 is a totally awesome ratio for the track with a 10.5 x 28 slick.


One concern - if I manage to reach my 400 HP goal, that type of gear and slick could hang the hoops if it runs a decent 60'.

So will the front settle in before it has to be shifted?? Who knows. Hope so.

Ive gotta give props to those who do it regularly - Power shifting with the wheels in the air is a bit of a balls steel operation. it's not a question of if something goes wrong but when. But it sure is fun.

Slamming down the nose will be very hard on frontend parts if I end up in that boat.

[Haystack]

Going with a t56 double overdrive later on? 4.56's and don't look back.

[martin0660]

When you say you have to shift to 5th .... what is driving that?

As an example, my junk runs the best numbers when I shift 6400 1-2, 2-3, and 3-4, but with a 28" tall tire, and 4.30 gear, I cross at 6700 RPM ... Car is still quickest / fastest this way (well past power peak). I have tried lots of combos, and in the end running through in 4th past power peak just doesn't hurt anything, and in fact is quickest.

4.10 for the win as far as I'm concerned. I am running the Motive in a 4.30 and have had no issues. When I was 26" tires and 4.10 gears, with a FMS gear, they was noisier. The 4.10 seems to be a little louder no matter who made it.

[erratic50]

I'm looking at top speeds achievable by a given gear at a given RPM when I say 5th must be avoided. The rpm drop is way too much so it is definitely 4th for the win - agreed.

I do plan on eventually going to a T56 with a Viper spec 0.5:1 6th but this is a long term thing. I need to finish redoing the mechanicals then do a full body and interior redo of this rusty and ratty old horse of mine before a 56 is ever a consideration.

In the end I am shooting for a high 10 or low 11 second car that can reconnect the front sway bar after getting kicked off the track then put on corner carving tires and do some CAM SCCA or put on street tires and drive anywhere at above typical interstate speeds.

And maybe do a standing mile run sometime too.

Of course with the mile the T5Z is just a bad choice as there is no way to have enough R's left to only run 1-4. That is a better scenario for a T56.

I guess it doesnt need to make sense to anyone other than me.... lol. And whatever it does I'll most likely be very happy just for having my car back better than ever once it's done.

I'm surprised to hear motive gears aren't making a ton of noise. I've heard a few sets that were done right and they were still nasty loud.

Thanks for the input all