Cobra4B

Drove the parents vert from Greensboro to Atlanta then to Kiawha, SC this past week and noticed that it was turning lower RPMs on the highway than my Z. At 75 mph the car was only at 1600 rpms, while my z is just under 2000. Also, I got 32.5 mpg and the Z gets 28.5 mpg... just wondering?

I thought the mn12 tranny had lower gearing for 1-3 then the rest were the same?

0rodney@rpmtransmissions

All ratios are different except 4th which is 1:1 M6=.50 M12=.56

Cobra4B

Thanks, but why would 5th or 5th be geared lower?? they're both overdrive gears, and are for highway cruising??? I would want the highest geared 6th gear possible :yesnod:

BQuicksilver

I've always wondered the same thing. I can see keeping 5th lower to accelerate, but I love the huge 6th on the MN6. It's kept me from looking for MN12's...that and the greater torque the MN6 supposedly handles.

Bertrand

5th may be an overdrive but it isn't just for cruising. You get to 170 mph much faster with the shorter 5th gear gearing. As for 6th, it only takes a few mods to make the Z06 a 200 mph car (like a turbo...).

The target market for the Z06 is usually people who care more about performance than 1-2 mpg on the highway. For comparison, a Ferrari 360 Modena gets about 14 mpg on the highway...

Finally, the fuel economy difference isn't just the rpms, it is also the better aerodynamics of the none Z06 vettes and their narrower tires with less rolling resistence than our Supercars...

LTC Z06

LS1/MM6 LS6/M12
1st Gear 2.66:1 2.97:1
2nd Gear 1.78:1 2.07:1
3rd Gear 1.30:1 1.43:1
4th Gear 1.00:1 1.00:1
5th Gear 0.74:1 0.84:1
6th Gear 0.50:1 0.56:1
Reverse 2.90:1 3.28:1

The main difference in 6th gear is our higher rear end gear, I can't remember the specs but we are 3.47 or so and a normal C5 is low 3s or high 2s.

CJS

All stick shift C5's have 3.42 rear end gears from the factory. Check your ratio in your Z06, maybe someone put 3.73's in it.

Guest

6th Gear: 0.50:1 0.56:1

6th gear is slightly lower in the Z06 than in a spec C5 with the 6 speed. Combine that with the 275 EMT that is approximately 1/2 taller and you have a much higher 6th gear effect in the spec M6 C5.

When I do the math, I should a difference of about 250 RPM between a Z06 and a C5 MN6.

Cobra4B

250 rpms seem about right... it makes sense that the taller tire coupled with the lower gear would make the difference I'm seeing. As for aerodynamics, this was in a convertible with the top up for half and down for the other. With the top up it has the same profile as the Z.

Tom Steele

I'm just guessing here, but I suspect that whatever gear in the path that lowers the first three also affects 5 and 6...

If you ask me, 3.73's would have been an easier, and better, way to go on the Z06. But GM didn't ask me! :)

Guest

You are right in that 6th is a higher gear than 5th. Sometimes some people refer to a lower gear as a higher gear and a higher gear as a lower gear.

A lower numeric value would be a higher gear. A 3:42 is higher than a 3:73!!

Corellian Corvette

Interesting topic. I will say that that 250 RPM makes all the difference for me and makes freeway driving a lot more enjoyable in my Z then my coupe.

Here in Washington state, the freeway limit is 60. In my '99 coupe, 60mph in 6th gear was miserable, it was just a little too low RPM and I was always hunting gears - otherwise it would lug and forget about passing...

With the Z, 6th is perfect at 60 and I still have decent revs to pass without having to downshift...

Just my observation.

Grayvette2

I believe that 6 th gear is the same on both the C5 and Z06 but the rear tires are different in size and rolling radius. The 295/35R18 rear tire on the Z06 roll 801 revs per mile while the 275/40R18 EMTs on the regular C5 roll 781 revs per mile. The regular C5 rear tire are taller which is the same as being geared a little faster all other things such as top gear ratio in the transmission and final rear end drive ratio being the same. Honest it does make a difference and the Z06 will be reving a little higher in 6th gear at a given road speed. I've had both and noticed the difference. It would appear that I'm getting about 1 to 2 MPG poorer fuel milage in the Z06. Still 27 + isn't bad all things considered. It's about 10 MPG better than my wife's Escape. :steering:

Guest

Actually, the 6th gear is not the same in the Z06 and normal C5. Couple the lower 6th gear and a tire wth a lower overall height and you get the difference in 6th gear RPM.

4-speed automatic 6-Speed manual 6-Speed manual
Application: Std. on coupe and conv. Opt. on coupe Std. on Z06 only.
1st Gear 3.06 2.66 2.97
2nd Gear 1.63 1.78 2.07
3rd Gear 1.00 1.30 1.43
4th Gear 0.70 1.00 1.00
5th Gear -- 0.74 0.84
6th Gear -- 0.50 0.56
Reverse 2.29 2.90 3.28
Final drive 2.73 (std) / 3.15 (opt) 3.42 3.42

PeterK

I've noticed that too. I actually can't even get 28 mpg if I keep average speed above 75 mph, while my 99 C5 always got over 30 mpg.

Another thing I've noticed by going on 2K miles trip that Z06 speedometer UNDER estimates the speed by about 1.5-3mph vs. my GPS navigation system.
I've ran this system on my 99 and they were withing 1 mph from each other.