Is my power limited off the brake?
 

Took my truck to the track over the weekend, just for fun. I wasn't even going to run but some of my friends talked me into it. I decided hey why not, I've got a couple little things done, lets see what she will do.

Truck is a 2013 GMC Sierra SLE. 5.3L, 6speed auto, extended cab, reg bed, 4x4, 3.42 rear gears. I DO have 275/65/18 Nitto Terragrappler G2's on it, so they are about a half inch bigger than stock. I have a AFe CAI, borla type s cat back, and a tune my buddy did on HP tuners. We did not mess with tranny at all, mostly VE and PE and spark tables.

Truck trapped 88mph pretty consistently. Best ET was 15.9 and my 60' was 2.4 or 2.5 each time...

I would "launch" in 4 hi, and switch to 2wd after shifting to second. Best time was loading the converter and getting some slack out of the driveline. Revs held at about 1500 to do this. Drop the brake and slam the gas.

Nothing happens though... it feels like all the timing is being pulled or something. No tire spin or fanfare at all it just slowly leaves the line, no matter what I do.

Is this because of the stock converter or is it torque management, or something else?

Torque management can be partly to blame but there also isn't a huge amount of grunt off the line with the stock cam setup.

If you post the tune file here through a google drop box or something I could look at it or even someone else to see if anything else could be adjusted to help it any.

I know with traction control off and stabilitrak off in my truck I can do a pretty decent burnout off a stop in 2wd. I've found the key is to not sit on the converter to get a good launch. The timer doesn't start untill you break the beams so you can pause a second and take off. I basically just use both feet like you normally would but in a real quick motion foot brake rev it up and take off right away. Only foot braking for less than a second.

I've tried loading it up to 1,500 but it just takes off like a slug.

OK cool, I'll get the file pulled and see if I can post it. I also tried just stomping the pedal and not reving on the brake at all but that was 16.1, same mph.

I've noticed the same thing on the street... If I give it part throttle from a stop, THEN go WOT it starts to scream. It really doesn't like WOT from a stop for some reason.

Comparison:
My buddy has a 2015 Silverado 5.3 crew cab. CAI, cat back and custom tune from a shop here in NC. We were dead even at the track on our fastest run. I treed him so I won but...

On the way TO the track we did a 45 roll and I left him like he was standing still. On the hwy I hang with or beat a ton of cars that are 14 sec cars on the strip.

Some people on the HP Tuners forums say you can "skew" the electronic throttle control settings to open the TB blade quicker but there is always a possibility of bricking the computer or going into REP all the time. I do not wish to take that chance on my daily driver, buying a new computer isn't something I want to do.


The only other thing kind of slowing it down is the heavier tires you are running., not alot but some.

Some transmission changes could help as well, quicker/smoother shifts could get you minimal gains and a transmission tune is easy enough on the 6L80e with stock engines. They are pretty blah from the factory.

It is definitely torque management/abuse management hurting you. Truck will still be slowish with those tires (and it is basically stock with a basic tune), but should at least be peppier.

I would figure with heavy tires and launching in 4HI that adds a massive amount of rotating mass. Plus during weight transfer if the front starts spinning slightly then traction control will come in and rob all your fun.

Pretty common these days for pedal torque requests to be clipped when the brake is applied.

I suspected the tires could be hurting me some... and don't get me wrong, I know this is basically a stock truck. I just thought I should be able to cut a much better 60' time in 4 hi. Like at least down to 2.2 or so.

I'm going to do a 2/4 drop on it next spring along with a rear sway bar. Def. long tubes and hi flow cats. I'd really like to get into the motor and delete DOD with a proper kit and redo the valvtrain and put a decent cam in it but I may not have funds for all of that.

So I got this pig down the track in 15.7@89mph on Sun. WITH the big Nittos on lol. I was happy with that. I pulled the tailgate and the spare off and surprisingly not even a tenth. What finally did it was putting it in manual mode and limiting it to 2nd gear and manually tapping into third gear and winding it out. I don't think it was hitting 4th gear before but maybe it was? It's a pretty mushy shift and maybe I missed it? I dropped 2-3 tenths and gained 2mph whatever it was.