Ive got a lil problem here. i have a sierra 5.3l ext cab with a flowmaster cat back and pacesetter LT headers. ive also got a diablo tuner and a cold air intake. i just installed the long tubes and it seems like the truck isnt as responsive. any ideas what might be wrong?

 

Flowmaster and 3" tubing killed the low-end. Dump the Diablo for a custom tune and you should get some of the loss back.

 

I'm assuming that you're using the Pacesetter 3" Y pipe. My belief is that the pacesetter setup is simply too much for the 4.8 and 5.3. I felt it was too big on my 6.0. The diameter of the pipes is such that the exhaust velocity is actually decreased resulting in decreased low end responsiveness. If you do a lot of racing though or live up high in the RPM range, the 3" pipe is actually pretty good. But for overall daily use I personally prefer a 2.5" pipe. Another issue is that you should probably get a custom performance tune and ditch the handheld. Adding headers does require slight tweaks to the tune to get optimal performance.

 

for what its worth, when i put on my pacesetters and ory, i was 0.6 faster in the 1/4. i think its all in the tune, get a custom tune like BOSS302 said

 

x3 on the tune!! custom tune makes a world of difference

 

get ahold of a diablo tuner.they can send you a custom tune via email that you load in your handheld then load to your truck

 

Yeah, i have all the supporting mods in my sig for a 5.7L LS1 GTO and i still think that 3 " would be too much for my car. The Magnaflow Cat back with 2.5" is good for over 500 hp.......115 cfm per sq in and 2.2 cfm per hp needed...............heck a SINGLE 3" would be good for about 375 hp.........

 

this is all very interesting to me.... still learning here, but what is the recomendation for us 5.3L guys?

I dont want to loose low end power as that is where i spend 75% of my time. Does the loss of power come from the Primary, or the y pipe? the factory pipe all the way back from there is 3"... isnt it?