Shifter6

This thread stems from a previous thread regarding MZ6 vs MN6 gear ratios. I am posting this thread to expand on the technical aspect of that discussion. Just to be clear I do not want this to be a Z51 vs base vs F55thread. This thread is about transmission gear ratios and their relationship with an engine's power band. I am hoping the people experienced with engine and track tuning will chime in and add to the discussion.

Given a particular engine's power and torque output (say a LS2 for example) what would be the best overall gear ratios for acceleration? Now every given application will require different gear ratios for the best performance. Drag strips, road courses and various street driving will demand specific gear ratios for absolute peak performance, but are there some general rules for the best gear ratios overall? To keep things simple let’s stay with the factory rear end ratio of 3.42 (manual) and we can use the LS2 as an example. Almost all performance driving happens in the first four gear ratios, so I am not concerned about 5th or 6th gear for this discussion

Here is some data (approx):

LS2
400hp @6000rpm
400tq @4400rpm

MN6 transmission (C6 Base/Z06)
Max speed by gear (mph):
1st...56
2nd...83
3rd...114
4th...148
Rpm after redline shift:
1st to 2nd...4350
2nd to 3rd...4750
3rd to 4th...5000

MZ6 (C6 Z51/C5 Z06/ C6 GS) transmission
Max speed by gear (mph):
1st...50
2nd...72
3rd...104
4th...148
Rpm after redline shift:
1st to 2nd...4550
2nd to 3rd...4550
3rd to 4th...4550

Now all things considered the overall ratios here are pretty close and we all know the 1/4 mile performance is similar. Which ratios are a better match to the engine? Considering the power band of an LS2, peak HP and Tq, what gear spacing is better overall? What are the principles behind the reasoning: Rpm drop to peak torque? Rpm drop closest to peak hp? Those familiar with engine tuning/building and competitive track car design should be able to help here, vendors maybe?

REVAK

Generally speaking, almost every one experiences an overall increase in performance when going to a deeper [ bigger number] rear. The same should hold true for the trans. ratios with any given rear gear set. The sweet spot is pretty close to the stock set up. Too tall and you have a salt flat car , too deep and you have a dump truck. There are many variables, manual or auto trans, stall converter rpm, weight of car, climate, elevation, engine set up [ cam, heads, n/a or blown, nos, ect.] Most folks I talk to like 4:10's with the Z06 trans., Z51 trans, [mz6 ratios], is a mixed bag , everybody has their own preference, from the 3:42's to the 4:10's.

Rocket-J

FYI.
The base and Z06 have the same trans ratio in a MN6 trans.
The GS has a different trans ratio in, I belive it is called, MZ6. First gear total redution is about 10:1. Similar to the Automatic.
A good hole shot.
I am not familure with the ZR1 trans.

Rick@RKT Performance

Base and Z06 have MM6, Z51 and GS have MZ6. ZR1 has the MH3.

Here are the lay out of the gears and you can see the spread:

MZ6 MM6 MH3
2.97 2.66 2.29
2.07 1.78 1.61
1.43 1.30 1.21
1.00 1.00 1.00
0.70 0.74 0.82
0.57 0.50 0.68

Shifter6

Yes it would seem deeper overall would be better for most performance applications. But when you take a very specific application, like say 1/4 mile drag racing, using the two tans ratios above its not as clear.

The MZ6 trans has lower gearing across the 1st three gears and a larger jump to 4th. The MN6 has less of a gearing advantage off the line. The shift into second is very tall (rpm drop to 4350) giving another advantage to the MZ6. But then the MN6 gear spacing provides a shorter jump to third (rpm drop to 4750). And then I believe the MN6 has another advantage which it can run the 1/4 in 3 gears and the MZ6 needs 4. Seems like a draw overall.

We all know that stock cars with MN6 and MZ6 1/4 mile about the same. Unfortunetly I am not sure if anyone has done a scientific test using cars where the only difference was the ratios (same driver, same track, same weather, same day etc.) Another interesting test would be a drag race to 148mph. Since both ratios share the same 4th gear and both cars have to shift 3 times, determining what car reached 148 the quickest or reached 148 in the shortest distance would isolate the effect of the ratios. The difference may be so slim its nonexsistent.

07MontRedcp

I have a '07 with the Z51 option and recently decided to have the internals swapped for the stronger TR 6060 gear sets and I had a little trouble deciding on which ratio set I wanted to use. I finally went with the Z06 ratios, but upgraded my rear end ratio to a 3.73 which puts the 1-3 final drive ratios in almost the same identical territory as the MZ6, but improves the final 4-6 ratios. Something for you to think about.

BJK

TMyers

It is all based on application. In drag racing I think it is a wash, we see the biggest improvement there by changing rear gears. On a road track I would have to go with MM6 do to is closer gear spacing and the predominant use of 3rd and 4th gear. In autocross the nod goes to MZ6 because we primarily use 2nd gear.

But there are more variables at play here. One is power, can you put it down. Has you can see from the list more power allows you to go to shorter gearing.

The other variable is tire compound and comes from my experince in autocross. With stock run flats our even max summer performance tire like Kuhmo's all vettes are traction limited. On paper the MZ6 should be better but because of it is much easier to break the rear end lose it tends to be a was. This all changes with R-compound tires though. With my MM6 I find it much harder to launch the car and find it much easier to bog the car coming out of a tight corner. In this case I wish I had more power or the MZ6 tranny.

Shifter6

All good points. The other area you didn't mention was street driving. My car has the MM6 and its a mixed bag. With such a broad power its not like it has any trouble pulling 1st or 2nd. At the same time, when you can reach felonious speeds at the top of second gear some enjoyment is lost. If the car could stick the power I got to imagine the lower first three gears of a MZ6 would be more "fun."

What I am wondering though, is there any rules to apply here. I mean just looking at the stats of a LS2/3 motor and the rpm drop of both gear set, is there a theoretical "better match".

Somewhere some engine builder/ track tuner uses guidelines when setting up gear ratios. Whether its rpm drop to peak tq or rpm drop to between peak tq and peak hp. Someone knows how to use the ratios to achive highest average power for a given distance.

Again I may be splitting hairs here because obviously both gear sets work from a pratical stndpoint.

JoesC5

For me, I would rather have higher gear ratios in the transmission and lower gear ratio in the rear end. That way, you have less RPM drop between gears, yet the over all gear reduction is the same. Since all the transmissions have a 1:1 4th gear, the lower rear end gear helps acceleration in 4th gear, no matter which transmission is used.

I would rather have the 2.66 Z06 transmission with 3.90 rear gear(10.37 total in first gear) then the 2.97 Z51/GS with 3.42 rear gear(10.16 total in first gear). With with the GS/Z51 transmission/3.42 the total reduction in 4th gear is 3.42, but with the Z06/base transmission/3.90 the total reduction in 4th gear is 3.90 That makes 4th gear much stronger in acceleration, and the 3.90 also helps 5th gear acceleration a bunch.

In 6th gear the 2.97 GS/Z51 transmission, with the 3.42 rear gear = 1.95 overall ratio.
In 6th gear with the 2.66 base/Z06 transmission, with the 3.90 rear gear = 1.95 overall ratio.

Both setups would have the same RPM while crusing down the interstate at 70 MPH, thus the same gas mileage, but the 2.66 with the 3.90 would have better acceleration in 4th & 5th gears.

topend182

Very good post. I personally have the mm6 gearing and wish it was a little more steep. For the recreational pull on the street, it is difficult to get into the power band for speeds between 15-50mph. Sometimes at 20-40mph I just want to downshift and go, but since downshifting into 1st isn't an option, I am left with a lackluster powerband in 2nd. I concur that the mm6/ 3.90 rear would be great for maximum enjoyment and efficiency.

Shifter6

3.90s will help, but there is still a large gap between 1st and 2nd. From a traditional sports car setup you can see why it would be set up this way. On a large road course I would imagine you would never be below 60mph effective making the 1st-2nd shift a non issue. Then you have progressively close gear spacing through 4th gear getting you up to 148mph. I can't imagine 5th is necessary on most tracks.

The MZ6 gear set favors speeds from 0-104 mph, what most Corvette drivers are doing 99% of the time. The tradeoff being the 3-4 shift and the drop to 4550rpms whent he wind resistance is higher. This is the "hole" of the MZ6 trans, at least in theory. I would guess because of: the low drag coefficiant of the C6, the relatively low weight of the car and the broad tq curve of the LSX motor, the theory mostly does not play out in reality. Another reason, is look at C5Z06's on the road course, even on larger courses with speeeds in between 100-140 mph it doesnt seem like that car is lacking anything.

Overall I would say:

MM6>MZ6
Faster road courses (barely)

MZ6>MM6
Most street driving (below 104 mph)
Autocross
Slower road courses

I would call drag racing a draw for the reasons above. Of note, back in 05, GM specs the Z51 car a tenth faster but that could be tire advantage.

Streetk14

Well, I've actually had both gear sets in my '08. It was a factory MZ6 car, which I bought basically stock. In stock form, the Z51 gearing was great. Steeper gearing to get out of the hole and close gearing on the 1-2 shift. But the larger rpm drops on the 2-3, 3-4 and 4-5 shifts are a disadvantage compared to the standard MN6 gearing.

I did a cam/bolt-ons and eventually a blower. With 650+ whp, I found the MZ6 gearing too steep in the lower gears to put power down on the street, even with very sticky tires. It also had a noticeable hesitation on the 2-3 shift at WOT (~6800 rpm shift point) as the revs would drop to 4700 -- or lower if any tire spin was present before the shift.

I eventually broke the transmission and have a C6 Z06 drivetrain in the car at the moment. At first I didn't like the taller 2.66 1st gear on the street with my cam. But then I realized the taller gearing really made the power more usable and the closer ratios help keep my engine where it wants to be. The 2-3 shift keeps me right at 5000 rpm, and I don't feel that hesitation that was there with the MZ6 gearing.

The real advantage the MZ6 has is the smaller rpm drop on the 1-2 shift. But we are talking 200 rpm here, and at the speed the car is going on this shift (~50 mph), the engine has no problem recovering. For me, it's a non-issue. Either gearset roasts the tires in 1st gear on the street, so 1-2 shifts at WOT aren't something to really consider for me.

I ended up having Rockland Standard Gear rebuild my original MZ6 transmission with MN6/Z06 1-4 gearing with a .80 5th and .50 6th gears. Should give me very strong performance up to 190+ MPH, and a nice cruising gear for MPG. Here are the spreads on my original trans and new one - all with 6800 rpm shifts:

Z51 MZ6:

1-2 = 4750

2-3 = 4710

3-4 = 4760

4-5 = 4830

MN6 w/ RS gear overdrives:

1-2 = 4550

2-3 = 4960

3-4 = 5220

4-5 = 5441

TMyers

Overall I would think you are correct for the driver that can drive at 10/10.

Shifter6

good info...

So would it be fair to say you like the MZ6 gearing when the engine was closer to stock?

Neumonic2002

Very good thread OP!

Out of all the combo's mentioned I think my car would benefit most from 07MontRedcp setup.

corvet786c

Hey spin you gonna chime in here?

Turbo6TA

07MontRedcp

Exactly what I did, but then I changed the rear end ratio to 3.73 to make everything a little stronger across the board. (See post #6)

BJK