REVHARD

Just curious on who has had good experience with the 2.66 gear set in there C5 Z06. The m12 2.97 gearing from the factory is really good with bolt on power upgrades and tune in my opinion. My car made 393/378 as an example and I mainly use 3rd and 4th at my local tracks.

But has anyone ever "upgraded" to the C6 Z06/MN6 gearing with this power level? I'm debating a gear set change but have a feeling it will be a dog out of the turns at my power level. I am planning a heads and cam upgrade which should bring me to about 420/400 whp in terms of power level. I feel increasing the torque and power will make the 2.66 a better fit but I may not actually do the power upgrades until late this year or early spring next year.

The trans will be out this week for a rebuild and was curious on peoples thoughts? Any regrets, pro's con's? If anyone is familiar with Michigan local tracks I usually run Grattan, Gingerman, waterford hills and M1 concourse. Top speeds don't usually exceed 130-135mph on the longest straights. The rear gear will remain as is at 3.42.

MySR71

I'm familiar with Grattan and Gingerman and I would say it depends. I'd consider how much time you spend on or near the rev limiter. At Gingerman for example, with 645 diameter rear tires, a stock rev limiter and around 385-400 rwhp, I'd hit the rev limiter between turns 2 and 3, right around turn 4 and hold it until turn 5, and going into turn 10b. With an MN6 and 7000 rpm rev limit, I no longer hit the rev limiter in any of these places. And I no longer have to shift from 3rd to 4th between turns 11 and 1 (the straight with the start/finish line).

At Grattan, I'd hit the limiter on the back "straight" and it was always awkward coming out of the last turn because I'd hit the rev limiter just before straightening out. With the changes (MN6 and higher limiter), these are no longer an issue. The only particular downside is that the revs can drop a little low in 3rd in places like the hairpin at Grattan so it might be more advantageous to shift into 2nd places like this. However, maybe I should be shifting into 2nd in the places with an M12 too.

I can probably dig up some before and after videos at Gingerman if you'd like to see.

REVHARD

Every single turn at both tracks you have just described I'm having the same issues. Only became apparent the faster I'm getting. Bouncing off the rev limiter and just flat out running out of gear. Causing an unnecessary gear change for a split second to 4th. I'm running a 315/30/18 NT01 which is I believe 26.1" same size as 645 essentially.

Thank you for your help. I was leaning towards the 2.66 then was having second thoughts. I think it will be a good upgrade for the future.

MySR71

I agree that at those tracks, it becomes more of an issue as a driver gets faster. I have no experience at the other tracks (Waterford or M1).

Scooter70

Darius - I prefer a 660 tall tire with the MN12 ratios just for the reasons that Dan pointed out. It gives you a few more revs at the end of all of the straights at GingerMan, Grattan, and MidOhio. I think if you have the option now, it might benefit you to swap to the MN6 gearset and then you can stick with the 645s.

REVHARD

Yeah, I was admiring the 660's on your car last week at Gingerman. I was thinking it would be nice to run a tire that tall or even a 305/675 or 315/675. But the economical setup is the 645 diameter or 30 series sidewall for me...jjust fits better in the front too for easy rotations.

MySR71

Unfortunately, the issue will get worse the faster you and the car become.

Gordy M

The last time I say Danny Kellermeyer in his C5 car at Grattan and Gingerman he was running 390 gears in the rear. He was running 315/30x18's in the rear and felt that optimized his speed and times, especially at Grattan.

REVHARD

Then I would think kellermeyer is most likely running the 2.66 set or the GM race trans set which is similair. But also on the other hand he races at waterford hills religiously and that's an extremely tight track. The best combination I've calculated is the 2.66 gear set with 3.73 rear end for grattan and gingerman...but it's out of budget at this time to do a rear gear also.

Gordy M

This year Danny is going to run his C7, it was about ten years ago when he last ran his C5 so all that has changed.

Supercharged111

Though the throttle may feel softer exiting a corner, the actual difference in acceleration is very difficult to quantify. In my racing class, we have strict power and weight limits and it's a real eye opener to chase a car with a different setup and still have zero difference in straight line pull leaving a corner.

6SPEEDZ

The MN6 is the best economical trans to go with for the track. The M12 is simply a magazine gearbox. It's meant to impress journalists to sell the car. Ideally the GM race box or ZR1 ratios with a 3.73, 3.90, or 4.10 is the way to go. But the ZR1 trans is expensive plus the conversion into a C5 and the diff gear change. This is why a lot of people go with the MN6 it has tighter ratios then the M12 and like Dan said you won't run up against the rev limiter at places like the Grattan back straight or the Mid Ohio front straight. Now playing with tire size also helps but it won't fix the wide ratios of the M12.

REVHARD

I priced out the parts for the MN6 1-4 swap...I pooped my pants a lil'

For those that dont know or in the future would like to know. You need:

input shaft
cluster
1st gear
2nd gear
3rd gear

The M12 5th and 6th gear shaft is one piece and can be reused and works just fine.

I also cried a little when they ran my credit card lol