ZBass28

I've noticed a few things different with the trans since I put the Gibson catback on the other day.

On WOT runs from dead stop or rolling the truck will now shift 1-2 at 5600rpms, before it was running all the way up to 6K on tach...I can definitely feel it shifting short. Is this normal?

For the most part, the trans feels like it is shifting better than it was before, other than the WOT shifting.

Has putting the new exhaust on somehow changed shift patterns, and if so, why and what can be done?

Mongoose Z-71

I believe 5600 is normal for the new gen GM trucks. Mine has been at 5600 before and after exhaust. I don't see how yours was shifting at 6000 unless it was changed with a programmer.
Maybe someone else can straighten me out, but I don't think so.

01 Silverado

When I put my flowmaster cat-back exhaust on my 4.8 silverado it shifted at the same RPM's, but did shift easier and quicker. Me and some of my Silverado friends agree that the tach's in our trucks suck pretty bad, becuase ours are a little different even from the same kinda truck and engine. I have never heard of someone shifting at 6K stock, and 5600 seems a lot more accurate for the stock shifting point.
Good luck <img border="0" alt="[Truck]" title="" src="graemlins/gr_truck.gif" />
Kurt

ZBass28

Well, I can certainly agree that the stock tach is a little off, but I am positive the truck is now shifting much earlier than it was previously. I can see it on the tach (which used to visually show shifting at 6K) and I can definitely feel it with the ole butt-o-meter, it doesn't nearly rev as high as before.

Perhaps the tach was showing 6K before and shifting at 5600 and now it's showing 5600 and shifting lower than that, but there is a most definite difference. It used to concern me before when it would run all the way up to the 6K mark before shifting so I know it was something I was seeing.

Anyhow, is there any possible way that the lack of back pressure could cause this? I can't possibly see how but stranger things have happened I guess.

01 Silverado

hmmmm... that is pretty weird, I bet the back pressure has something to do with it, maybe take it to a mechanic friend of yours or something... I will talk to mine Monday and see if he's heard of it. Did you do anything to mess with the cats or O2 sensors??

ZBass28

Nothing else on the truck has been touched so far. The truck was completely stock when I put the Gibson on. It is strange because I can feel during normal driving that the trans shifts better than it used to, but at WOT it's just too early on the 1-2.

01 Silverado

Thats pretty weird... I will try and talk to my mechanic bout it tomorrow and see if he has heard of it before.
<img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />

CMNTMXR57

Tom, that's not unusual as the engine doesn't have to wind up as much before shifting into the next gear. Essentially it's not having to work as hard.

I've noticed that on all my automatic trans equipped vehicles after installing an exhaust.

ZBass28

Oh wonderful....this thing basically now is shifting just when it really starts pulling hard, at least compared to before.

Hypertech time I think <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />