1996 bronco with a LS swap. I should be making around 500/450. On the motor. I’m mounting up hooker blackhart manifolds which are 2.5”.

If I run duals, I have to route the driver side to the passenger side due to the transfer case and a frame mounted air tank.

the question is duals or a y pipe? If duals, what size - 2.5”? If a y pipe, 2.5” to 4”?

The goal isn’t max horsepower; it is torque. I’m leaning towards the y pipe but would like some input. The truck will mainly be used for overlanding. Either way I’ll be running borla mufflers and no cats.

 

Y- pipe, 3" pipe starts to get minor restriction at 500HP level, below that level 3" is basicly invisible.
Overlanding suggests quiet, full over the axle, out the back system. BIG diesel spec 3" muffler will be quiet, and non restrictive.
You turbo, supercharge or start trying for 600 HP you'll NEED to step up at least 3.5"

 

definitely no power adders. Short wheelbase and high center of gravity.

 

I have a 98 Wrangler with LS6/4L60E combo. Small cam so maybe 425 hp at the crank.
I used block hugger headers. For the same reason you have I had to route the left exhaust tube around the front of the oil pan and merge with the right exhaust tube then into a Flow master "Y". 2.5" inlet and 3" outlet. All mandrel bends to get around the oil pan. Then 3" all the way back to the bumper. Biggest/longest Dyno Max turbo muffler I could fit. Its been 15 years but I believe I used a 2009 Grand Cherokee V8 3" tail pipe. It's mandrel bent. Had mod it a bit to fit but it has worked well.
Pic.

 

On engine masters 3 inch y into 3 inch single with very smooth transitions was quite a bit better than 2.5 dual. 2.5 inch y was not very good.

Check out Engine Masters Season 5 Episode 7 Single vs Dual Exhaust.

 

Y pipe w/ 4in single. Go big once👍 I'm doing dual 3in to single 4in now on my TBSS.

 

I have done a lot of exhaust systems in that power range dual 2.5 with a X-pipe as close to the engine as possible if peak performance is the goal. Not a single fan at all, I had a 423 HP SBC in my 1990 RS that lost about 40 hp into a single 3" exhaust system even with a great merge Y and a good 3" catback with a good free flowing muffler. My 1980 C3 with a 400 hp small block responded extremely well to IIRC it was Pypes 2.5" dual kit and long tubes. I swapped the crossmember for an aftermarket setup for dual exhaust.

My 1997 stock 350 was dual 3" to the muffler but the manifolds had 2-1/4 outlets and stock 3" cats. When I replaced the cracked manifolds and put Thorley tri-Y headers on it the stock cats had failed from all the fuel being dumped in by the 02 sensors reading lean. Put 3" high flow cats and a dual 3" in/single 4" out muffler and 4" tailpipe for a GMT800 8100 truck on it. Stuck with the factory 3" dual tubing on that one because it was heavy gauge mandrel bent stainless from GM and Thorley included connecting pipes that bolted to the headers, had brace brackets that bolted and suspended the exhaust systems weight to the 4L80E and their tubing eliminated the goofy and massive resonator ahead of the RH catalytic converter. It was a very good setup except the flanges of the headers and connecting pipes should have been V-banded rather than using garbage factory style donuts and bolts with lock nuts in almost impossible places to put any kind of socket or wrench on. HUGE shot in the arm to that stock 350 though. Now has a 500 hp 383 exhaling through it without any real restriction.

I have had several other engine combinations that ran great with 2.5" duals and a X-pipe or dual inlet muffler. The 400+ HP 350 in my 87 G20 van has 2.5" duals to the muffler through 2.5" cats into a dual in/dual out magnaflow, very smooth sounding and great power.

My 2011 M56S made 428 whp and 434 wtq through the stock exhaust manifolds with their close coupled factory cats and a 2.5" dual system with a X-pipe where the stock Y-pipe resided and 2.5" magnaflow magnapack mufflers where the resonators sat. Did the same exact exhaust on my 2007 G35 Sedans VQ35HR (7,800 rpm V6 FYI) as well except had headers and high flow cats. Ended up having to add 2 more magnaflow mufflers at the rear of the car to make that VQ somewhat quiet cruising and even then at WOT it was boarderline obnoxiously loud. Neither the V8 or V6 was restricted in anyway by the exhaust and both gained torque across the whole rpm range with the 2.5" dual systems.

G35



G20


97 Express 350 OE 3" dual system complete with restrictive resonator.

 

Would have been interesting to try on my 3rd gen that lost ~40 of its 423 hp with a 2.5" to single 3" Y-pipe. I think a lot is lost in those cars because of the weird angles the Y-pipe has to bend to clear various obstacles. Almost like GM designed that cars chassis and then remembered it needed an exhaust system. I had a used SLP system I found like new identical to the one in this article and a Random Technology catalytic converter on it because I had to stay with a single cat to pass visual emissions at the time. The catalytic converter probably cost some power and I know the catback did too. Picked up like 17 rwhp with an open 3" cutout.