Pumba

Gentlemen,

At 7:30 p.m. last Tuesday night my Z completed a journey that started at the 2013 North American International Auto Show. At that show Chevrolet debuted the 2014 C7 Corvette Stingray. While other show attendees were gathered around the new Stingray, I was focused on a cut away display of the new TREMEC TR6070 7-speed manual transmission that would be available in the C7 Stingray.

I had read about the new Stingray offering a 7-speed trans, so I took my camera and a tape measure to the show in hopes that Chevrolet would have a cutaway model of the trans at the show. They did, and I took pictures of the trans from various angles and took pictures of it while place a measuring tape along its length.







As soon as I got home from the show I fired off an e-mail to Rodney and Jeremy at RPM Transmissions and asked them how the length of the 6070 compared to the 6-speed 6060 trans. They got back to me right away and told me that the 7-speed was 1.75 inches longer, and we talked about what it would take to install one in a C5. The consensus was that we would need to shorten the torque tube, driveshaft, and shift rod the same 1.75 inches. Unknown at that time was whether the bell housing on the rear end of the torque tube would fit in the tunnel once the torque tube had been shortened.

Later in the fall of '13 RPM purchased a completed TREMEC TR6070 transmission and did a teardown. What they found was that the 5th gear of the 6070 trans was narrower than the 5th gear found in the 6060 trans, and hence any 5th gear that TREMEC offered for the 6060 trans would not fit in the 6070 trans. So my choice of the 5th gear was made for me, unless I wanted spend big $ to have a custom 5th gear made.

In further discussions with RPM, we decided on the gear set for the 7-speed I wanted to have installed in my Z:

- 1st: 2.66:1
- 2nd: 1.78:1
- 3rd: 1.30:1
- 4th: 1.00:1
- 5th: 0.74:1 - The stock 5th gear in the base Stingray trans
- 6th: 0.63:1 - This gear came from my existing 6060 trans
- 7th: 0.42:1

Over the winter of '13 - '14 RPM gathered the parts we would need to do the conversion:

- A new TREMEC TR6070 Export transmission:




- A new The Driveshaft Shop carbon-fiber driveshaft that had been shortened by 1.75 inches:




- RPM sent out a C5 torque tube and had it shortened by 1.75 inches and ground off the exhaust hanger strap fastener bosses:




On Tuesday, May 6th, at 8:00 a.m. I was at RPM's shop in Anderson, Indiana. Led by Wes, and assisted by Guffey, Kurt, and Jeremy the RPM team worked tirelessly for the next 11+ hours to complete the conversion.

The removal of the existing C5 pieces went quickly. Because I had a slipping dual-disc clutch, the RPM team also installed a new American Powertrain SCIENCE FRICTION Atomic Twin Kevlar clutch assembly and one of their SCIENCE FRICTION Billet Steel flywheels.

RPM also took the time to shorten my existing C5 shift rod:




Here is a close-up of the weld that RPM did when shortening the shift rod by 1.75 inches:






There were some noticeable differences between the 6-speed 6060 trans and the new 7-speed 6070 trans. The first is the reverse lockout mechanism:

6060 Reverse Lockout







6070 Reverse Lockout







Next is the location of the trans pump.

6060 Trans Pump - Output Fitting




6060 Trans Pump - Feed to Gear Head Unit




6070 Trans Pump Output Fitting and Feed to the Gear Head Unit



Notice how the outlet and inlet to the Gear Head Unit on the 6070 are both on the driver's side of the trans. This cleans up the package and shortens the hose.

Next, Wes installed the trans-diff assembly on a lifting cradle and slid them into place in my Z.




The last remaining challenge was to relocate the Exhaust Pipe Spring Hangers. On a C5 they attach to the rear torque tube bellhousing:




In the shortening of the torque tube, we were required to move the hangers to a location at the junction of the bellhousing and the transmission:







We were also required to move the attaching straps further to the rear on the X-Pipe:







At a little after 7:30 p.m. Rodney took my Z for a ride to verify that it was safe to drive.

On the way down to RPM I had set my cruise control at 76 mph. My engine rpms with my 4.10:1 diff gear and the 6060's 0.55:1 6th gear was 2,300. With the 6070's 0.42:1 7th gear my engine rpms at the same 76 mph was 1,700. My fuel economy improved by over 15%, and the Z was much quieter on the highway. And the 6070 upshifts and downshifts are much easier to perform than the same shifts on a 6060.


The only item that we will need to adjust in the build is The Driveshaft Shop's carbon-fiber driveshaft. They do not supply any rubber couplers with their unit or the option to install rubber couplers. On the drive home, the NVH from the driveshaft was very objectionable. I will be purchasing and having RPM install a new carbon-fiber driveshaft with rubber couplers.
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tlove32

Awesome writeup.

Telepierre

Interesting project!
Thank you for the write-up.

My turn to get hold of RPM...

tcruse

Very nice.

lowellmstevens

Was your goal to lower cruising speed RPMs? Or were other reasons involved? I see you mentioned having 4.10s so I can understand why you would feel that your RPMs with the 6-speed were still too high for long highway drives

Pumba

My goal when installing the TREMEC 6070 7-speed transmission was two-fold:

> 1) I want better gear spacing between 4th and 5th and between 5th and 6th gears. I don't want my rpms to fall in a hole on any of those two shifts. By not falling in a hole I should be able to achieve my goal of driving my Z to 200+ mph.

With my 4.10:1 diff gear ratio and my Michelin Pilot Sport 2 325/25R20 tires, which are 26.4 inches in diameter, I will achieve the following speeds in the first six gears at 7,000 rpms:

1st -- 50 mph

2nd -- 75 mph

3rd -- 103 mph

4th -- 134 mph

5th -- 181 mph

6th -- 213 mph

With 700 SAE engine horsepower I should be able to reach 200 mph.

>2) I want a quiet cabin and the improved highway fuel economy, between 70 to 80 mph, that a 0.42:1 7th gear (4.10:1 x 0.42:1 = 1.72:1) will give me.

MY03C5Z

Very nice detailed write up, looks like a cool project. Sounds pretty pricey, mind me asking what this cost?

apollo240

Got a thread with pics and details of your car?? I like where your going with this. Sounds like you want a c5 z capable of running/beating todays cars, yet still streetable and comfy.

MotoJB

Seriously awesome...

RC000E

10grand for 7th gear....seems legit...

Pumba

Talk to Jeremy at RPM Transmissions - (800) 406-1109. He can breakdown the costs for you.

Pumba

View my Garage - http://forums.corvetteforum.com/memb...11-albums.html
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Pumba

It costs less than that.

PeteZ06

Only because you already started off with a TR6060 in your car.. otherwise this project is right at $10K I'm sure.

Pumba

The only added cost a TR56 trans owner would have would be the cost of broaching his pinion gear from its present 27 spline configuration to the modern 30 spline configuration that is used in 6060s and 6070s.

FYRARMS

Nice write-up for sure. Definitely not the swap I will ever see being a necessity for my needs, however. Too many current easy drop-in replacement transmissions/diff gears available to net me the speeds and rpms I would want, and at a much lower price point. I do see a ZR1 TR6060 and built C6Z diff in my future, however...

Telepierre

Wow - Inspirational car for sure.

Question on the objectionable NVH: is it just noise to the ear or do you both ear and feel the vibration on the car?

I had noise due to vibration stemming from a new S/C install which went away after a hundred miles or so... maybe you want the system to settle first..

007Duc

Man, I'm dissapointed. No electronic diff conversion to go with that 6070?! Ha Ha

Pumba, you never cease to amaze me what you've got cooking on your vette.

Pumba

The driveshaft is VERY objectionable in both noise and felt vibration.

After I returned home, I talked to another C6 owner who had one of the same driveshafts. He said people would come up to him as his car was idling and ask him what was wrong with the car. After he took out The Driveshaft Shop carbon-fiber driveshaft, and replaced it with a CF driveshaft that had ZR1 couplers the noise and vibration were gone.

momo20

Pumba I love reading your write up's so much information, and love how you are willing to try things that other's won't very nice ride and keep the one off mods coming!!!