Cat Man HHR

Hi
Thinking of getting the GMTU for my stock SS automatic.
I would like to know what changes take place vs in stock form.
I know more boost is there but does the auto trans have different changes also?
I don't really see myself getting a cold air package or an exhaust upgrade.
Thanks

dphi8705

Granted... I'm not an owner yet... but, I've done a ton of research and figured I'd chime in with some of what I've read to at least give you a bump in case I'm wrong...

The GMTU is a selection of sensors and connectors coupled with a dealer ECU flash. This will effectively increase your boost to an average of 20-21PSI. The increased boost will lead to more usable horsepower and torque within the meat of the powerband. Most are seeing slight increases in MPG as well due to this.

It will NOT alter shift points. An aftermarket tuner (HP I believe) can add this function.

2005HHRauto

Nooo don't do it….

The GM tune was ok when it 1st came out, as most wanted to
keep the factory warranty , & there wasn't any aftermarket "tunes",
available.
Now, with the LNF being a very "mature" platform, "tune" wise, talk to
CJ about a Trifecta "tune", or find a tuner, that can tune you with HPTuner.
No need for the GM 3 bar sensors anymore.

Hay dphi8705, shift points are changed with the GM tune, RPM limiter is
increased to 6,400

Cat Man HHR

Thanks for your input on this.

russruth

I've gone three routes.

First the gm tune which the dealer messed up and spliced the wires wrong.

I paid for a complete new harness and used crate engine depot's pigtales so the wires would not have to be crimpled or soldered and that fixed most of the problems, though the bottom sensor still hit the air conditioner so the dealer flipped the sensor 180 degrees and that fixed the problem.

Next went with trifecta for more power, which I got a good tune, though had horrible torque management issues, with a very abrupt shut off if I nailed it at lower speeds. Vince couildn't disable torque managment because he said he only had a 2009, and couldn't write the torque managment out of a 2008.

So then I tried HP tuners and hired a long distance tuner recommended by the cobalt and hp tuners forums. Both his tunes were way off, just dead off the line and around mid range just went nuts at 24 lbs then back down quickly. Strange thing is the HP tunes I bought fell off after a few weeks and required a reload every so often.

So bottom line is I just run the trifecta tune and don't jump on the throttle or run the stock gmtu tune.

I personally think these cars are very sensitive and the only way to do it right is to either be very good at tuning yourself, or take it to someone that can tune, drive the car, maybe dyno it and get it solid and correct.

Anything else is just chasing your tail.

BTW: I tried reaching 2005HHRauto who is every helpful but his mailbox was full.

All the above is just my opinion and other's have different results.

Cokeybill

A little late, but I had the GMTU installed on my 08 ss shortly after I bought it new. I had some lower sensor probs until the 180 switch. Since then (6 and a half years later) I still see 22 on my boost and is solid whenever I WOT, still goes liked a scalded frog. Some of the Colbalt guys in my area are pretty impressed with how my SS still performs with the GMTU even after all this time.

bigjacksauto

x2
basically the same experience here
after the 180 degree switch of the lower tmap sensor
and having my PCV valve replaced the car has been running flawlessly
still capable of running a 14.0 in the quarter with little traction until around
80 feet out.

still need to install one of 2005hhrautos tunes