I want 3.91s

[zlathim]

Originally Posted by acammer

4th either way. A 1LE with the MM6 trans gear ratios, stock 27.85" tall tires and 3.91 gears will go 106mph at 6500rpm in 3rd. A regular SS with M10 gear ratios, stock 28.66" tires, and 3.91 gears will go 99mph in 3rd. A bolt on M6 car will go well over 110mph, so you're going to 4th. With stock 3.45's a near stock M6 car can get it done with just third some times, but once you add some power and the trap speed climbs, you gotta make the shift.

So then, the 4.10 is the way to go without a doubt from a quarter mile perspective, you're gonna be in 4th any way you look at it even with a bolt on car, and you want all the RPM you can get in 4th. A 4.56 would even be appropriate, but nobody makes one that can live in such a small housing.

Take some time and play with gear ratios - there is a lot to learn. This is a great calculator here.

Here are the trans ratios and tire sizes:
M10 (regular SS) ratios
1st: 3.01
2nd: 2.07
3rd: 1.43
4th: 1.00
5th: 0.84
6th: 0.56
Final: 3.45
Tire: 28.66" diameter

MM6(1LE SS) ratios
1st: 2.66
2nd: 1.78
3rd: 1.30
4th: 1.00
5th: 0.74
6th: 0.50
Final: 3.91
Tire: 27.85" diameter

Thank you for taking the time to type all of this out. It helps me a bunch and I truly appreciate it.

[zlathim]

Originally Posted by acammer

Why would you not go to 4.10's? Motive makes a good gear set that many of the fast guys are running with good success. On a stock sized tire you're still under 2000rpm at 70mph. I lost about 1-1.5mpg on the highway, and no real loss of economy at any sub-highway speeds.

It's the best mod I've ever done on my car - if you're going to go through the trouble of doing gears, why not take all you can? I did them when I was bolt on and it transformed the car. I can't imagine going with less gear than that in the M6. There isn't a downside that I see, all upsides.

With regard to the rest of the logistics you'll definitely need the full install kit. I wanna say that the ring and pinion was about $330 from motive, and maybe another $300 for the install kit.

Another thing to strongly consider is doing a different carrier - the stock posi is well known to get weak and end up a "1 tire fire" unit over time. JRE does make a kit to tighten up the clutches. Alternatively, Eaton sells the TruTrac ($610) carrier which is a gear based posi which is quite a bit stronger.

While you're beefing things up, an LPW diff ($240) cover is an option to consider. It's a cast steel piece that gives some much needed strength to the weak aluminum factory case. Additionally, it has load bolts that help hold the ring gear caps in place. JRE does make a billet set of main gear caps, but the LPW cover solves for the ring gear caps issue and helps strengthen the entire case for a similar price.

RDP has some really good black Friday promos going right now that might save you some money...

OK, I'm leaning toward doing everything that you mentioned. If it's not too much to ask, please take a look at my parts list and tell me if I have everything I need. I added the prices for anyone looking that might be interested. These prices are from the RDP store and unfortunately the black friday promo code does not apply:

Motive 4.10s pt # MOTG886410 - $332.15
Detroit TrueTrac pt# 912A686 - $611.99
LPW Ultra diff cover pt# 201-10IRS- $239.99
Richmond Gear install kit pt#83-1079-1 - $249.99

Total $1,434.12 (+ labor)

Am I missing anything? A local shop quoted about $400 for the install, so I should have less than $2k in it when its done.

[Chris49066SS]

Nice combo of parts, a little jealous right now, I need some good stuff too!

[zlathim]

Originally Posted by Chris49066SS

Nice combo of parts, a little jealous right now, I need some good stuff too!

Thanks, man! I'm looking forward to getting this project together. Will probably order some parts today.

[dreksnot]

Originally Posted by acammer

Why would you not go to 4.10's? Motive makes a good gear set that many of the fast guys are running with good success. On a stock sized tire you're still under 2000rpm at 70mph. I lost about 1-1.5mpg on the highway, and no real loss of economy at any sub-highway speeds.

It's the best mod I've ever done on my car - if you're going to go through the trouble of doing gears, why not take all you can? I did them when I was bolt on and it transformed the car. I can't imagine going with less gear than that in the M6. There isn't a downside that I see, all upsides.

With regard to the rest of the logistics you'll definitely need the full install kit. I wanna say that the ring and pinion was about $330 from motive, and maybe another $300 for the install kit.

Another thing to strongly consider is doing a different carrier - the stock posi is well known to get weak and end up a "1 tire fire" unit over time. JRE does make a kit to tighten up the clutches. Alternatively, Eaton sells the TruTrac ($610) carrier which is a gear based posi which is quite a bit stronger.

While you're beefing things up, an LPW diff ($240) cover is an option to consider. It's a cast steel piece that gives some much needed strength to the weak aluminum factory case. Additionally, it has load bolts that help hold the ring gear caps in place. JRE does make a billet set of main gear caps, but the LPW cover solves for the ring gear caps issue and helps strengthen the entire case for a similar price.

RDP has some really good black Friday promos going right now that might save you some money...

^^^ Best explanation I've seen around this place ^^^

[zlathim]

Originally Posted by dreksnot

^^^ Best explanation I've seen around this place ^^^

You're telling me. I came in here wanting 3.91s and ended up with 4.10s and a TrueTrak. I just ordered everything from DynoSteve. Coolest guy ever and he made me a great deal even though there isn't a lot of margin on these parts.

[dreksnot]

Originally Posted by zlathim

You're telling me. I came in here wanting 3.91s and ended up with 4.10s and a TrueTrak. I just ordered everything from DynoSteve. Coolest guy ever and he made me a great deal even though there isn't a lot of margin on these parts.

Read your comment as I'm opening up my box of goodies from him: ID fuel filter, AEM wideband. I've had exceptional performance by him on orders.

[LCPLPunk]

I have 3.91's in my L99 and I love it!

[Black_SS10]

I installed my new diff not long ago. 3.91, trutrac, lpw cover, and poly bushings. Makes the car feel much lighter and much more fun.

[zlathim]

Originally Posted by Black_SS10

I installed my new diff not long ago. 3.91, trutrac, lpw cover, and poly bushings. Makes the car feel much lighter and much more fun.

How does the truetrak compare to the factory clutch style posi?

[alice]

Believe it or not, I have 4.88 gears in a Hammer Head diff! WaveTrac posi unit and carbon fiber driveshaft from DSS. I'm a v-6 twin turbo with 4200 stall FTI converter. It's a bullet!
Still cruises beautifully on the freeway. Love the tall gears with the OD tranny. Best of both worlds.

[Pro Stock John]

Only other thing I had to get were carrier bearings when I did the Eaton TT.

[The camaro show]

Originally Posted by alice

Believe it or not, I have 4.88 gears in a Hammer Head diff! WaveTrac posi unit and carbon fiber driveshaft from DSS. I'm a v-6 twin turbo with 4200 stall FTI converter. It's a bullet!
Still cruises beautifully on the freeway. Love the tall gears with the OD tranny. Best of both worlds.

how much power do you put down, tell us more about your set up

[acammer]

Originally Posted by zlathim

OK, I'm leaning toward doing everything that you mentioned. If it's not too much to ask, please take a look at my parts list and tell me if I have everything I need. I added the prices for anyone looking that might be interested. These prices are from the RDP store and unfortunately the black friday promo code does not apply:

Motive 4.10s pt # MOTG886410 - $332.15
Detroit TrueTrac pt# 912A686 - $611.99
LPW Ultra diff cover pt# 201-10IRS- $239.99
Richmond Gear install kit pt#83-1079-1 - $249.99

Total $1,434.12 (+ labor)

Am I missing anything? A local shop quoted about $400 for the install, so I should have less than $2k in it when its done.

That all looks right to me. I went with Motive's install kit because I wasn't sure if there would be any differences, but if Dyno Steve signed off on that, I would have zero concerns.

You'll love the change - it's dramatic and exciting. The other thing I don't think we ever talked about was that you'll need a quick adjustment to the tune so that the speedometer reads correctly. I would think since you already have the dynosteve remote tune he should be able to make that change for you without any trouble.

Glad you guys all liked the write up. I see a lot of M6 cars end up with 3.91's and I can't wrap my head around why guys don't just go 4.10s. Back when we only had Richmonds and their quality issues then sure, I wouldn't risk it either. But Motive makes a quality set that seems to stand up pretty well, and there's no other downside.