what size exhaust for ls

[nacho55]

I'm taking my truck down in the morning and wanting to get suggestions on exhaust pipe size and muffler selection, this is a stock motor for now but will most likely be getting some upgrading after its on the road a bit.
Thinking 2.5" or 3" duals.
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[Clyde65]

I have 2.5 on my stocker ls swap
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[85burb]

I would go with 2.5 inch. I put a 2.25 duel set up on my lq4 with cam and different intake and it is way way to small. Sounds like junk. I am saving up for a 3 inch mandral bent exhaust now. Right now it sounds like glass packs but i have flowmasters. It really upsets me.

[68GMCCustom]

I have 3.0" dual setup from the header reducers all the way back to the rear axle. Its in a genIV 6.0L swap warmed up with a hotter cam.

really depends on your motor tho. smaller LSx (4.8, 5.3, 5.7) could use 2.5" for some growing room, the 6.0/6.2 and up can use 3".

[Super73]

I would run 3" if it is performance based. 2.5" if you can do dual cut outs.

[BR3W CITY]

I'm running 2.5", but its a true dual so restriction isn't a concern

[nacho55]

Thanks for the imput, i guess i should of specified, it's a 5.3 truck motor stock for now but I can never leave enough alone.'
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[usmcchevy]

I'm running 2.5" full mandrel duals. I would guess I'm good until 450-500hp.

[Super73]

So with my old 347, with a 3" X-pipe through Warlock Mufflers I made 43x peak hp at 6,900. With the Warlocks opened I made 449 rwhp. TQ was the same from 2,500 to 4k but started to pick up beyond that rpm picking up 17ftlbs at peak (5,600rpm).

I have dyno'ed quite a few stock 5.7's with headers and various exhaust systems. Every one with a dual 3" and dual electric cut outs lossed 0ftlbs TQ and picked up from 3,500 on to peak hp.

I think a modified 5.3 would be better off with a well set up dual 3" system.

[crazy longhorn]

A true dual, should support 450hp on 2 1/2" pipes....& it wont be too big for your 300-325hp mill. I agree, the 6.0/6.2 can handle more(bigger) pipe, but on the smaller cube mills,you will give up the low end tork,running the big pipes. I have a 5.3 to drop in my old truck, & will run 2 1/2"pipes crazyL

[Super73]

Longhorn,

Just curious if you have dyno numbers or track results of different combos to quantify your claim of loosing TQ down low with a bigger exhaust pipe. I'm not saying there isn't a pipe tooo big, but I can tell you from my experience on they dyno and at the track with various combos/vehicles, there is nothing to loose going to a dual 3", at least on a 5.7, even with stock cam/heads.

Heck, my 418ci motor lost TQ under the curve and at peak going from the 3" X-pipe to dual 2.5".. Luckily I have dual electric 3" cutouts before it steps down to 2.5" so it picks it right back up. Only reason I went to a 2.5" from the 3" X-pipe was to quiet it down a bit.

I will be testing my buddies 60 panel with a 5.3 swap at some point. It will wear my old 1 3/4 stepped to 1 7/8 headers and my old 3" X-pipe with Warlocks. For fun, I will stick my current 2.5" exhaust on it. I will be happy to show dyno results when done.

[crazy longhorn]

Originally Posted by Super73

Longhorn,

Just curious if you have dyno numbers or track results of different combos to quantify your claim of loosing TQ down low with a bigger exhaust pipe. I'm not saying there isn't a pipe tooo big, but I can tell you from my experience on they dyno and at the track with various combos/vehicles, there is nothing to loose going to a dual 3", at least on a 5.7, even with stock cam/heads.

Heck, my 418ci motor lost TQ under the curve and at peak going from the 3" X-pipe to dual 2.5".. Luckily I have dual electric 3" cutouts before it steps down to 2.5" so it picks it right back up. Only reason I went to a 2.5" from the 3" X-pipe was to quiet it down a bit.

I will be testing my buddies 60 panel with a 5.3 swap at some point. It will wear my old 1 3/4 stepped to 1 7/8 headers and my old 3" X-pipe with Warlocks. For fun, I will stick my current 2.5" exhaust on it. I will be happy to show dyno results when done.

No, I sure havent done any dyno time, or track testing , but I would be interested to see the results This is my 1st "rodeo" on the LS engine, so I am here to learn I would be curious, about hp/tork # on the 418 ci that you are running(bet shes a beast)! crazyL

[68GMCCustom]

I agree with what you're saying Super.....but life "on the street" is different then going WOT on a dyno, or at the track.

An engine is living from just off idle to what?..... say 3800rpm or so (depending on configuration)...running at just 2/3 throttle or less for most drivers, or if wide open, at 100% throttle for just a few seconds, not WOT for a full pull.

I would have to say this is something verified by experience.... and your own "on board dyno".......... good old SOTP.

[Super73]

SOTP doesn't always tell the truth.
Sometimes things "feel" faster because you just spent some hard earned money on it, but then the track times reflect differently.
Or sometimes things feel slower because they are loud, yet track times reflect they went faster.

If I get the chance, when I dyno his 60 panel, I will limit the throttle body. It wouldn't take much to do a 1/3 pull, 2/3 pull and a 100% pull for both exhaust systems. I am always up for an experiment.

[68GMCCustom]

it would certainly answer some questions...