Anybody Running a 3.89 Rear Gear?

[GT Premi]

I've noticed that there's a noticeable gap in acceleration force between 3rd and 4th gear on these cars. I never really noticed it before, but many mods later, I'm seeing that the stock 3.55 is taking some fun out of high speed blasts. Don't get me wrong, even with the 3.55, my car still pulls HARD, but you all know how we do. Once we get used to it, we want more! We all know that first gear is pretty much useless for hard acceleration on these cars outside of a prepped drag strip and slicks/drag radials. So 2nd, 3rd, and 4th are the play gears. On the highway, it's really just 3rd and 4th for most situations.

It would be nice, if the transmission gears were better spaced. Seeing as how re-gearing the transmission isn't practical (or is it?), I'm thinking a more aggressive rear gear will make 4th more exhilarating and even bring 5th gear out to play a little bit. I'm considering a 3.89 or 3.90 rear gear.

Is anybody here running one of those ratios? If so, how do you like it? Where'd you get it from? I don't want a 4.10 because the GT500 doesn't have enough revs to make that aggressive of a gear be practical on the street.

Thoughts? Recommendations?

 

[CD07GT500]

Power? Weight? Tire height?

 

[GT Premi]

Power = 650+RWHP (conservative guess)
Weight = ~3600 lbs
Tire height = not a clue (285/35ZR 19 Michelin Pilot Super Sport)

 

[CD07GT500]

That is a 27" tire so you could still do ~140 @ 6800 with the 3.90.

 

[biminiLX]

I run close to a 29" tire and it makes 4.10s closer to 3.90s.
'13-14 trans is much better geared for my preference, and the cams are different regarding revs, but I think your 2011 would still like the 3.90s
-J

 

[GT Premi]

I have the rev limiter on mine set to 6500. I don't want to press it passed that.

 

[13COBRA]

Power = 650+RWHP (conservative guess)
Weight = ~3600 lbs
Tire height = not a clue (285/35ZR 19 Michelin Pilot Super Sport)

What'd you do to get down to 3600lbs?

 

[GT Premi]

What'd you do to get down to 3600lbs?

A list longer than my arm. Dropped a little over 100 lbs in rotating mass alone. Plus suspension bits and interior.

 

[13COBRA]

A list longer than my arm. Dropped a little over 100 lbs in rotating mass alone. Plus suspension bits and interior.

Couldn't tell if racial joke, or?

I bet that thing moves out. I would go with a 3.73. There are a ton more cars out there running a 3.73 compared to a 3.89/3.90. Keeps your top end there, and gives you quite a bit more seat of your pants feel.

 

[GT Premi]

Couldn't tell if racial joke, or?

I bet that thing moves out. I would go with a 3.73. There are a ton more cars out there running a 3.73 compared to a 3.89/3.90. Keeps your top end there, and gives you quite a bit more seat of your pants feel.

I don't get it. But yeah, my GT500 somehow runs like a scalded dog. I can't even really explain it. All I can say is it scares the crap out of me sometimes. LOL Not because it feels out of control, but because jail cell speeds come up in the blink of an eye.

 

[GT Premi]

So, after some research, I've ordered a Torsen T-2R LSD and a Motive 3.90 ring and pinion set. Too many people were raving about the T-2R's handling improvements to pass it up. And since I'm having the gear changed, anyway... My only small concern is that a few people complained about the Motive gears being a bit noisy. But many others were saying they have no issues with them. I'm betting the people with noise didn't replace the clutch packs or maybe had worn spider gears. Since I'm putting in the Torsen, I won't have any of that to be concerned with.

Sent from my BBD100-2 using the svtperformance.com mobile app

 

[Jam421]

I'm running a 28.75" tall rear tire with 4.10's which = 3.90 rear gear. I love the feel of 3rd/4th gears & highway cruising is awesome.

 

[GT Premi]

Well, i got the Torsen T2-R and the 3.90 gears installed. (That was a big bill!) I'm still doing break-in miles (500) for the ring and pinion, but my initial impression for the T2-R is that the hype is real! I can now get on the gas mid-corner and the rear end doesn't try to swing out on me. That's not mashing the throttle to the floor, mind you, just applying some moderate throttle in a turn doesn't result in fishtailing or the rear kicking out anymore. Now I get some very mild push. I might need to loosen up the rear sway bar a little bit. If you're someone who likes to drive spiritedly and loves curves, the Torsen T2-R is well worth the investment.

I briefly considered an Eaton Tru-Track(?), but looking at how it and the Torsen are designed, I felt like the Torsen would behave more like I want. They both use some very interesting design methodology, and I think both are probably very good. The Torsen just looks a little bit more robust in the way it works. I'm assuming the price delta is a result of the difference in robustness. The Eaton looks like it might be prone to slippage or not transferring power as efficiently in some situations.

Now about the 3.90 ring and pinion; it doesn't really seem as much of a step up as the ratio would have you think. I thought my revs would be almost uncomfortably high around town. That's not the case at all. The revs are still very much around-town friendly. In fact, it actually made my GT500 a little bit easier to drive with the SPEC Super Twin 3-puck clutch setup. Acceleration-wise, I haven't noticed much difference yet. Again, I'm still in the break-in phase and haven't romped on it or winded it much past 4K yet. Maybe a little less than 4K RPM for now. So I don't have anything worthwhile to report in that area yet.

The Motive gears are very whiny. I believe they're becoming slightly less whiny as I put some miles and wear on them, though. After a couple thousand miles, they might quiet all the way down. We'll see how it shakes down after I've put enough miles on the setup.

 

[biminiLX]

I usually stay don't fear the gear with mod motors and heavier new Mustangs. As you're taking it easy, you're probably noticing the extra mechanical advantage of the gear makes the car more responsive and feel lighter. Glad you like the mods.
-J

 

[me32]

I usually stay don't fear the gear with mod motors and heavier new Mustangs. As you're taking it easy, you're probably noticing the extra mechanical advantage of the gear makes the car more responsive and feel lighter. Glad you like the mods.
-J

Exactly dont fear the gear