Thread: Tranny Upgrade Results: HP Tuners, Torque Management, MPG

Yeah, fitting the LS6 takes, time, money and a rubber mallet. The fuel rail is the big problem, cause the LS4 rail doesn't fit without extensive massaging and the LS6 fuel rail uses taller injectors and doesn't clear the alternator bracket. And it's not close. Anyway, I finished mocking it up last night and once I make sure there are no particles in my manifold I'll bolt it up tonight.

After a week of driving the car around and tuning the shift pressures, I have a couple thoughts. First, I for sure get better mileage in the 45-65 range (mid 30s instead of low 30s), about the same at 70, and a lot worse above 75. The left lane to work typically cruises at 80 or so, and I get about 19mpg on average at that speed compared to about 22 before. Going 65-70, I'm in the high 20s low 30s, and I can hold that mileage at 75 if I'm following somebody. So, as long as I don't speed, I get the same or better mileage. Not a bad deal considering how much more get up and go I picked up (12.3% more torque at the wheels in every gear, by the numbers).

I'm having a lot of fun with HP tuners. I turned some torque management back on in normal mode to save the tranny, and left it all off in performance mode (tap shift). I also put a shift RPM in performance mode (6100RPM) so I can drop it into tap shift and safely rip off a max acceleration. I've seen guys say you can safely go to 6200RPM with the stock valvetrain, but I don't want to push it to the limits. I also used higher shift pressures in performance mode. I'll probably wear out the half-shafts, but they're much cheaper than transmissions. Maybe some of the 3800 guys can comment, but I'd imagine that there are aftermarket half-shafts when the time comes.

For the 05-06 guys, you should really look at the 07-08 spark tables in DOD mode. I pulled a stock 05 cal from HP tuners, and it had less advance than V8 mode. My car has significantly more advance in DOD than V8 mode, and way more than the spark curves of the few tuned cals I found out there. Stock V8 mode advance looked the same for all years. I need to find someone with a wideband O2 sensor before I do too much with the engine cal, but once I bolt up the LS6 I'll pretty have to tune it too.