: Auto Trans Question

08-25-11, 01:06 PM
My Vagon should be delivered around the 1st of September, so forgive yet another newbie question, if this has been asked and answered previously.

I recently read that the automatic transmission cars are limited to 179 top end, as the transmission will not shift into 6th, while the 6-speed will hit 191 MPH in 6th gear.

Why is this? Will the auto tranny not take the abuse in 6th? Or does the drag on the car not allow it to pull this speed, with an auto? I had a 1991 ZR-1 (We used the hyphen, back in the day:)) and it would actually lose forward momentum if you shifted from 5th to 6th at high triple digit speeds...

Is there a way to "tune" the computer to allow it to go into 6th, once it red-lines in 5th?


08-25-11, 01:11 PM
I think it all has to do with the gearing and design of the auto trans. The gear ratio is different in a 6 sped manual as is the rear end axle (possibly).

The rear axle ratio for the manual is 3.73 and the ratio for the auto is 3.23.

Ratios are as follows for the auto tranny (6L90):
1st - 4.03
2nd - 2.36
3rd - 1.53
4th - 1.15
5th - 0.85
6th - 0.67
Rev - 3.06

Ratios for the manual are as follows (TR6060):
1st - 2.66
2nd - 1.78
3rd - 1.30
4th - 1.00
5th - 0.80
6th - 0.63
Rev - 2.90

08-25-11, 02:37 PM
Thanks for the info. So it's basically drag limited based on the gearing, and the computer 'knows' there no point shifting into 6th?

08-25-11, 02:50 PM
191 here, mortarforkers! Well, at least I think so...

08-25-11, 05:17 PM
I think it's speed limited. My auto will shift into 6th under power. I remember reading it was a heat-related issue on the auto trans also.

08-25-11, 07:11 PM
It's because some of the components can't handle the speeds, specifically the clutch basket and the output shaft iirc. After said upgrades, you're good to go to 191+

08-25-11, 10:24 PM
Automatics are limited to 171mph, I believe as a result of the output shaft not being able to withstand
the speed and rpms.

Best regards,


08-26-11, 05:10 AM
I have my V Coupe since March 24th and put over 12000 miles on it so I can tell a little about it.
It`s a 6 auto and the top speed is exactly 308 kph ( 191 mph ) it shuts off. (a friend with a 6 manual V Sedan had his up to 320 kph (199 mph)- no speed limiter and still a little room to go)
On the Autobahn when traffic allows it I`m mostly in the average speed of 100 - 190 mph. Had it to the 308 kph maybe 20 - 30 times since I have my V Coupe.
If I have it at about 240 kph (150 mph) in six`th gear and stomp on the gas pedal it shifts down to 5 th gear and goes up to 191 mph - lift of the gas the six`th gear will engage at about 150 mph.
Mine is the export model, hope I coule help a little.


Gary Wells
08-26-11, 11:32 AM
Cad CTS-V2 automatic versus manual trans data (as of 05-16-2010):

Manual trans (M6): Tremec TR6060 6 speed manual,
fully synchronized with single overdrive (MG9):
Gear ratios (:1) 1st: 2.66, 2nd: 1.78, 3rd: 1.30, 4th: 1.00,
5th: 0.80, 6th: 0.63, final: 3.73, reverse: 2.90

Gas Guzzler (GG) tax of $1300, or half that of the A6
Faster by 16 MPH (191 MPH versus 175 MPH (governed))
A tad slower in the 1/4 & on the street
A tad better *mileage* than the *auto* but probably not significant
About 38 more RWHP than the auto on the average
About 30 more RWTQ that the auto
About 95 lbs lighter that the auto
No remote start feature
Has “no lift-shift” feature

Automatic trans (A6): Hydra-matic 6L90E 6 speed
electronically controlled automatic overdrive with
torque converter clutch (MYD): Gear ratios (:1) 1st:
4.03, 2nd: 2.36, 3rd: 1.53, 4th: 1.15, 5th: 0.85, 6th: 0.67,
final: 3.23, reverse: 3.06

Gas Guzzler (GG) tax of $2600, or twice that of the M6
Slower by 16 MPH (175 MPH (governed) versus 191 MPH)
A tad quicker in the 1/4 & on the street
A tad worse mileage than the manual but probably not significant
About 38 less RWHP than the manual on the average
About 30 less RWTQ that the manual on the average
About 95 lbs heavier that the manual
Remote start feature
Normal mode initially starts in 1st gear, then starts in 2nd gear thereafter
Manual mode starts in 1st gear always

About 1 in every 6 ’09 CTS-V’s were / are manual trans (M6)

08-31-11, 01:32 AM
I have an '11 sedan and was just curious about this so I downloaded the ECM and TCM tunes out of my car with EFI Live. Keep in mind I have no idea what I'm talking about.........this thing has spark plugs; the EFI Live is for some diesel trucks :histeric: I don't see any place it says speed is limited to XXXmph (other than the 205 speed limiter, which we all know isn't going to happen). "Torque" limits in 5th gear? Is that what does it?

I don't give a crap about changing it, I'm not gonna drive that fast. Plus I need one unmodified vehicle in the driveway that has a good chance of getting me to work.

ECM Speed Limiter:


WOT Shift Speeds in the TCM:


TCM torque limits: