I've got an 08 mn6, and i'm about to cam it, then gears. I'm lookin to get 470 rwhp easily with suppporting mods. My questions are?
1. Does anyone have a 390 or 410 without problems like whine or having them replaced?
2. Which do I go for 390 or 410?
3. Or do I wait for another company to come out with one besides motive?
Thanx

 

I have an 08 M6 non-Z51 with 484 rwhp, cam, and gears. To change my gear ratio, I went with an RPM Transmissions Stage II rear diff with 4.10's.

I just got the gears installed a little over a week ago, so I can't speak of longevity. However, I do not have any noticeable whine nor do I regret the 4.10 ratio. I am glad I did not go with 3.90's.

2000 rpm on the freeway occurs around 77 mph.

-Donnie

 

3.90 gears installed by Horsepower Sales in Pompano Beach, FL. About 3000 miles now and no whine at all.

Either 3.90 or 4.10 and you will wonder why the factory gave us 3.42. The 3.90 gears will give you marginally better fuel economy on long highway trips.

 

I have the Motive 3.90's and they are as quiet as factory!
I'm glad I went 3.90 instead of 4.10's!

 

So I guess my 2.56's just suck ?

So that's where my 33 MPG came from

 

4.10's for me, no whine and I love them, wouldnt go any other way.

 

After doing tons of research, I went with 390's on my 08 Z51 Manual.

The first set failed around 500 miles. It was related to the Motive gear debacle. My shop (Cartek) suggested I wait until they were able to locate a "Good" set of gears; Max got to the point where he can tell visually if a set is sub standard. I'd finally received a call and they went ahead with the swap. I now have close to fifteen hundred miles on the second set and they are quiet as a church mouse. It is a GREAT mod!

 

Its all about the break in. If you heat cycle them properly about 5 times they will harden and mesh together well and you wont have whine and other associated issues.

 

4,10s for me Awsome no noise 3000 miles on them drive the car everywhere installed by Chuck Corvettes of Westchester the only way to go !!!

 

Dude - You must have an A6 tranny with 2.56 gears. If you change gears, you might want to go with 3.15 or 3.42 gears. You'll probably see lower mpg by 2-4 miles, but you'll have alot more fun.

 

Motive 4.10s here and no whine!

 

CUT AND PASTE FROM MICROSOFT WORD (since everyone says the same BS like this gear is waaaay better than that one):

If the car is going to be drag raced at a track, the 1/4 mile trap speed will be close to maxed out with 4.10's. In that case 3.90's would be the way to go. If its just a street car, 4.10's are the way to go. Keep in mind you will be spinning in 3 gears with 470rwhp and either gear set if you dont get an R-compound tire.

I'm over 700rwhp and love the 4.10's with MT ET streets. I hook fine and go. No whine. Most good tuners can manage a quiet final result.

The best advice I can give you is to drive or at least go for a ride in a car with 4.10's and 3.90's for you to see for yourself how exaggerated people make the difference out to be. Most guys with 3.90's never drove 4.10's and vice versa. Get first hand experience and dont get the wrong gears because someone insisted the difference was ridiculously better with one or the other. 3.90's give up 5% of the benefit of 4.10's off the line and 4.10's make you run 5% higher in rpm on the hiway. Some get hung up on one of the two issues and both are fine with the right tire.

As in all other gear set threads I post on, I always say that the one thing you must do is source the diff and the install from one and the same person/shop. If you do get a bad diff, the installer isnt going to take it all apart and lend you his lift while you wait for the diff supplier to get another one to you. He will charge double for the install and it isnt cheap.

 

I have a 08 M6 Z51 w/ 3:90's and really like them. On the highway I get 30+ MPG and at the track w/ GY runcraps I get mid-high 11's. Mine were bought and installed by EnglanGreen and sourced from RPM as a complete rear unit. More than 5K miles on them and no noise or problems to speak of.

 

4.10 Motive set. Car is a bolt on car - headers, mid pipe, Z06 cans, Callaway CAI, 160 degree thermostat, and a tune.

First set of 4.10s went bad within 300 miles. Second set in and quiet after 700 miles.

Even with the short gearing of the Z51 transmission, this is the way to fly. I just have to rework my launch because wheel spin is certainly more pronounced.

Gas mileage has drop 1 - 2 mpg: no big deal. Fun factor has increased by a magnitude of 10.

 

3.90s here. dead quiet, but new DTE stage II rear so I can't speak to longevity. Highway mileage appears to have dropped 1mpg, but the observation is not from a tightly controlled test.

Besides the fun/performance factor, stop and go traffic driving is improved as it is easier to creep along in 1st gear at low speeds.

 

Thanx for all the replies