So my set up so far is Ls3 480, 1 3/4 long tubes, 3” y pipe. My question, is there any benefit increasing the single exhaust pipe diameter after the y merge?

Thank you in advance

 

It wouldn't hurt but I think you'd also benefit from 1 7/8th headers on a engine that size.

 

You mean like not creating a choke point? That merge is your problem. I currently have a nearly stock 4.8L and cut off the stock collector and went dual 2.5" all the way, and there was a HUGE difference, especially up top. Now it just keeps climbing smoothly all the way.

I remember doing the math on here and I calculated my exhaust (being the OD - wall thickness and then getting cross area). Dual 2.5" is within 1% of a single 3.5".
Here:
(If a 2.5" pipe is measured by OD. 16g steel is .0625" thick. (x2 = .125" thick, 2.5" - .125 = 2.375" ID. 2.375/2 = 1.1875 radius. Pi R sq = 4.43 sq inches of ID area.
3" pipe - .125 = 2.875". /2 = 1.4375 x Pi R sq = 6.49 sq in of ID area.
3.5" pipe - .125 = 3.375 /2 = 1.6875 x Pi R sq = 8.946 sq in.
dual 2.5" pipe is (4.43 x 2 =) 8.86 sq in.
A 3.5" pipe volume is 1% greater than dual 2.5".


For a 3" pipe with 16g walls, = 6.491 sq inches of cross area (for dual 3" pipes = 12.982 sq in" of total cross area).

A 4" pipe is 4" - .125 total wall thickness for ID = 3.875 /2 = 1.9375 Radius
(1.9375)squared x pi = 11.793 sq in" of total cross area.

You have bends in there that are reducing the flow, but a single 3.5" can only flow 68% of what a dual 3.0" can do.

if that was me, I'm doing a dual 3" to a 4" collector, or even a 4 1/2" collector, or more likely getting rid of that merge and just running dual 3" all the way. If it's an air pump, why would you create a blockage, or a choke point to block air?

 

If I’ve already created the choke point with the 3” y pipe, I should just do a single 3” pipe into a good muffler and dump at rear bumper. Correct?

i know it’s not the perfect setup for top end but, will it at least help with low to mid range torque?

 

You will be fine with the 3” all the way out. Like mentioned earlier, you would need larger diameter headers to make any real beneficial gains from a larger exhaust downstream. I made over 500 rwhp with 1 7/8” headers to a y pipe to the factory exhaust with a magnaflow muffler.

 

Thanks y’all, I’ll be running 3” for now

 

Gen IV 6.2 trucks use a 3.5" single exhaust,

 

upsizing after a choke point only makes the exhaust note deeper.