Andork

Gang, I am *presuming* that the numbers at this site are accurate, but if others more in the know than I can chime in to validate or debunk them, all the better...

http://www.corvetteactioncenter.com/...008tr6060.html

Background:

When I drove the Z51 I *immediately* noticed its lower gearing. I was sold. Alas, they dealers in my area didn't have the car I wanted (LT1, Z51, MM6, black) so I opted for the Z51-less base model, figuring I can always go after market for the difference.

And so I'm now trying to choose between 3.90's and 4.10's - where the balance is between SOTP and gas mileage...

And considering that I immediately noticed a first gear difference of 0.3, I know that the 0.5 difference between the stock 3.42's and the 3.90's will give me plenty of STOP improvement while helping ease my mind about gas mileages - in that it'd be juuuuust that much better than 4.10's.... just the games I tend to play with myself!

Anyway, I thought the numbers and my simple analysis might be of help to others....

Andork

dennis50nj

i think for the z51 390 and 410 for none z51 on the LS3

glass slipper

Yes, the numbers in your link are accurate. You couldn't find a Z51/MN6 car because GM doesn't make them that way...if you order Z51, you automatically get the MZ6 transmission if it's a manual or the 2.73 rear end if it's an automatic. Also, the 2.66 1st with a 3.90 rear end is very close to the 2.97 with 3.42 rear end...2.66*3.90=10.374 and 2.97*3.42=10.157. You might like the 4.10s better.

MarkRx

that confused me. it says MZ6 for the 6.0L Z51, then what tranny is on my 08 6.2L LS3 Z51 6-spd manual? i was told MN6. makes no sense that a base corvette shares the Z06 transmission and that the Z51 tranny handles less torque. is it due to the gearing?

overrev64

Because of the added torque and horsepower of the LS7 engine, the Z06 doesn't need the more aggressive gearing of the Z51 cars. That is why it shares the same transmission ratios as the base car.

Craigster05

Maybe this will help ease your worry about gas mileage...Base MN6 with 4.10 gears on flat highway.

3 Z06ZR1

I have a non z-51 with 390's and love them. Great for track and all around with really no loss in mpg. still 84 mph at 2000 rpm. Puts you with the same overall 6th as the z-51. 1.95 vs 1.94 but lower and closer thru the rest makes an outstanding package. 4.10's put you at a
couple hundred more rpm's. Still not bad!

saplumr

I didn't need the Z51 for my power mods.

glass slipper

If you have the Z51 option, you have the MZ6 transmission.

In any transmission with the gear tooth width and countershaft/input shaft spacing already given, the torque capacity is determined by the 1st gear ratio. When you increase the 1st gear ratio, the output shaft gear gets larger (more teeth) and the input gear gets smaller (less teeth). As the input gear gets smaller, the torque/stress increases and there are less teeth in engagement which adds additional stresses. That's why the MZ6 transmission has a lower torque capacity. The only way to increase torque capacity would be to increase the width of the gear or increase the countershaft spacing both of which would result in a larger/heavier transmission. In spite of sharing the same gear ratios, the 2006-7 base Corvette and Z06 don't share the exact same transmission...the Z06 had additional strengthening/hardening to 1st gear and the input shaft. I don't know what (if any) differences there are for the 2008-9 base/Z06 models.

AirBusPilot

Looks like for 08' the base car and Z06 have the same identical transmission.

wildbill ws6/ss

so what gears do the z51 cars have if non z51 have 3.42 in the 6 speed

k0bun

All manuals have 3.42s. Z51 or not.

nearwater

Thanks for the in-depth explanation.
I'm not sure if I understood all that, but does this mean that the Z51 transmission(MZ6) is more susceptible to failure under heavy power modification?
Thanks,

Dan

catpat8000

An additional, and perhaps the most important reason for the Z06 transmission ratio choice is that with a 7000 rpm redline and the current ratios, it can hit 60mph in 1st gear. Any other ratios mean a shift before hitting 60mph, which would add some tenths to the advertized 0-60 times.

Pat

Wayne O

The Z51 option was designed for the parking lot autocross enthusiast. Its wider ratio gearing may not be the best option depending upon how your car is ultimately setup and what you intend to do with the car. Here's an old post from shopdog which I found interesting and which may shed some light on the subject:

"Z51 tranny has a 5.32:1 spread from low to high (2.97:1 from low to 4th). Z06 and base has a 5.21:1 spread from low to high (2.66:1 from low to 4th). The race ready car has a closer gearbox, and so does the base, compared to the wider ratio Z51, particularly in the 1st to 4th range which is what matters in almost all racing. Closer ratios mean the engine can be kept closer to the power peak in all out racing. Wide ratio boxes are typically found in trucks, where the granny low lets them more easily start off a heavy load.

But to be fair, the overall difference between the two transmissions isn't huge. What I find more interesting is what jschindler said about pulling above 100 MPH. The base tranny is approaching the top of 3rd at that point, the Z51 tranny equipped car has to shift to 4th to avoid hitting the rev limiter. So the base should actually be pulling harder. In the quarter, the base tranny equipped car is right on redline in 3rd as it crosses the line, the Z51 tranny equipped car has already had to shift. That means it is down on rear wheel torque by a factor of 0.769 compared to the base car at that point. A loss of 33% in rear wheel torque is significant."

Here's some 'gearing' information:

__GEAR______Model__or__Option
____________Z06___Std_6-spd___Z51_6-spd___6-spd_Auto___4-spd_Auto
__1st_______2.66____2.66________2.97____ _____4.02________3.06
__2nd_______1.78____1.78________2.07____ _____2.36________1.63
__3rd_______1.30____1.30________1.43____ _____1.53________1.00
__4th_______1.00____1.00________1.00____ _____1.15________0.70
__5th_______0.74____0.74________0.71____ _____0.85
__6th_______0.50____0.50________0.57____ _____0.67
Reverse_____2.90____2.90________3.28____ _____3.06________2.29

Axle Ratio___3.42____3.42________3.42________ _2.56_____2.73(or_3.15)

ENGINE<------Vehicle_Speed------------>
RPM...1ST...2ND...3RD...4TH...5TH...6TH
1000....8....13....20....27....37....47
1500...12....20....31....41....55....70
2000...16....26....41....43....73....93
2500...20....33....51....68....92...116
3000...23....40....61....81...110...140
3500...27....46....71....95...128...163
4000...31....53....82...109...147...186
4500...35....60....92...122...165...186
5000...39....66...102...136...184...186
5500...43....73...112...149...186...186
6000...47....79...122...163...186...186
6500...50....86...133...176...186...186

IMO the preferred transmission depends on how you use your car and the extent of modifications, if any.