No, that's not a good idea. You may increase exhaust velocity by doing that, but a single 2.5" will be a bottleneck. I think unless you are crazy about changing the exhaust is to leave it how it is and then focus on increasing the output of the motor. This will compensate for the bigger flow capabilities of the exhaust. The TR220 is the most widely recommended 5.3L cam and from what I've seen gives the best balance of power throughout the entire powerband. That cam and a torque converter of your choice and I think you'll be very happy.

 

well what if I keep the 3'' diameter but go to a single out instead of dual out? Would that help any?

 

Back pressure is very real, particularly in big power adder (boost namely) applications! The myth is that these late model trucks and cars don't have enough after swapping to a LT header and ORY with a good catback.

 

I have some vids but I couldn't figure out how to upload them. All I know how to post is this pic lol...



mine is the one closest to the camera

 

why's your tailgate down? That's your torque loss

 

you're joking right... lol

 

If you wanna step down anywhere, I'd say go to 2.5" at the collector all the way to the Y, then go 3" single after they merge. IMHO, 3" collector piping all the way down, even if merging into a single 3" for the rest of the exhaust, is costing you exhaust gas velocity in the lower rpm's.

 

You totally missed the point of my first response to the OP, I wasn't telling him to run a 3" pipe from the collector back to the Y, there are many y-pipes (stock included) that run 2.5" into the Y, then 3" out (excluding stock y, I believe it is 2.75"). I WAS NOT Talking about the collector size, I was telling him not to step down the 3" Y-out to 2.5" as that would cause a restriction in flow, it's hard to get that velocity back as you're decreasing pipe cross-section. So, do you still dis-agree with me???

Then you go and post this down below \/. Whats the deal?

If he want's his low end torque back then I agree, run 2.5" collectors to either a 2.5" IN /3" OUT Combined Y pipe, or run 2.5" Duals with an X or H pipe.

 

In that case, I must have misread your post. I agree with you. But I do think the stock Y pipe is 2.25" (at least on the NBS)

 

Thats what I was referring about. Where not talking turbo motors here.