Over 500hp.....3" exhaust...or 2.5"?

[68GMCCustom]

Need opinions on my exhaust system for my truck. Its a roughly 550hp LSx with 1 7/8" headers and 3" collectors/reducers. A buddy gave me some low use 2.5" turbo mufflers and is trying to get me to go 2.5" but my original plans were for a 3" system. There's really no room for an x-pipe (within the frame rails) so I had planned on running an h-pipe over/under the driveshaft yoke, mufflers in front of the CPP trailing arm crossmember with the pipes going thru the 3.5" oval holes in it. Not sure from there....exit out the sides in front of the tires with some ovals notched into the steps, or over the axle and dumped...out of sight.


I know I would probably get better torque out of a 2.5" system...but feel the motor might need the bigger 3" system to reach its potential while still being "muffled".

Thoughts?

[KQQL IT]

Id say 3''

[tonypaul]

I have a vortec 454 and nowhere near 500hp and I went with 3" duals but I also have stock exhaust manifolds with a 2 1/2" - 45 degree angle bends coming off the manifolds then goes into the 3". Im always thinking about the future, and future upgrades will be better with the 3". I bought a 3" x-pipe exhaust kit but I ended up not using it cause I wasnt going to be able to get the 'x' part tucked high enough into the frame. So I just ran duals and dumped in front of the axle....

[68 C-10 KID]

You should be able to run x- pipe easily under your truck. I normally Flange mine on the back side also to make the trans easier to pull out. I also say 3" Due to future mods.
The shorter the exhaust the louder is going to be. Longer the quieter its going to be.

[cableguy0]

Run 3 inch all the way. bigger exhaust will not hurt the torque output. This has been covered a bunch in a lot more detail in some other posts but bigger exhaust will only help not hurt. Let it breathe. Any small amount of torque you could possibly lose from running bigger pipes is already lost in your case with the 1 7/8's primaries. Just run 3" it will run and sound better.

[68GMCCustom]

Thanks all! You helped me confirm my original decision...and as much as my buddy wants to help...he can keep the 2.5" mufflers for another project. I'm going 3"!

[ProStreet68SB]

2.5" 2.5" 2.5" 2.5"!!!!!!!!!!!!!!

[68GMCCustom]

now you know someone had to come in and buck the status quo.

[ProStreet68SB]

hahaha yeah. Trust my advice

[68GMCCustom]

do tell.

this truck will be more of a "race" truck - toy....then any kind of "driver". I don't go anywhere daily.....so I don't have one of those DD things.

[tonypaul]

Go to the drag strip and see how many drag cars/trucks are running exhaust smaller than 3". Your engine is nothing more than a airpump, everyone in the racing scene is trying to make their airpumps breath better. Bigger valves, bigger cam, bigger exhaust, turbos, superchargers, ect to get it to breath better. Most will run open hedders or run cutouts on street machines to get the most out of their preformance. I think you need to worry more about getting a tire to stick more than worrying about how much more torq you can get with 2 1/2" exhaust.

There is no way I would put on a 2 1/2 exhaust sstem on my drag can and expect it to preform better at the track...

[cableguy0]

The smaller pipe=more torque thing is a wives tale/myth. Put up some dyno charts etc and prove that 2.5 will be better. The header tube size does have an effect but by the time the exhaust is past the collectors it doesnt matter.

[KQQL IT]

prostreet68sb keeps preaching 2.5
show us why 3'' is so bad

[v502]

I went with 3in on ls3.

I got 1 5/8 headers with 3 in collectors with an x-pipe and sounds amazing.

[68GMCCustom]

hang on now....I never said I wanted to run 2.5" instead 3"...quite the opposite. I didn't want to go 1 5/8" and bought large tube headers for a reason. And I'll probably run open headers at the track (I prefer to hear my own motor over the one beside me)....I was just trying to confirm my thoughts and get my buddy off my back about running the 2.5". This truck will drive to and from the track with the occasional just because cruise...and I'd prefer to let it breathe over trying to restrain it. I like to let 'em run when I find an open byway...

now I see this is another one of those areas that folks like to debate....

[KQQL IT]

Originally Posted by 68GMCCustom

hang on now....I never said I wanted to run 2.5" instead 3"...quite the opposite. I didn't want to go 1 5/8" and bought large tube headers for a reason. And I'll probably run open headers at the track (I prefer to hear my own motor over the one beside me)....I was just trying to confirm my thoughts and get my buddy off my back about running the 2.5". This truck will drive to and from the track with the occasional just because cruise...and I'd prefer to let it breathe over trying to restrain it. I like to let 'em run when I find an open byway...

now I see this is another one of those areas that folks like to debate....

No doubt^^^

[Super73]

Originally Posted by ProStreet68SB

hahaha yeah. Trust my advice

So with your line of thinking, I should have made more TQ with 2.5" over 3" right?

Why didn't I with the 347ci motor making 449rwhp and why don't I now with the 418ci motor making 521rwhp?

I'm all ears and always willing to learn why...

Torque for both motors was more with the 3" ALL THE WAY THROUGH THE CURVE starting at 2,400rpm where I began all my pulls..

[vin63]

...fit the largest diameter exhaust you can.

[68GMCCustom]

3" Flowmaster universal kit w/h-pipe and 3" turbo mufflers (my preference) on the way and will be here tomorrow! I just love Summitt...its here 2nd day w/o while paying for air...just $8 for "standard ground" shipping. Going behind my DynaTech 1 7/8" - 3" long tube headers....should sound mean but we'll see!


and for anyone thinking I should have gone with 2.5" for "torque" reasons.....this truck won't pull or haul anything heavy. I'll build another truck for that someday. Consider this more of a "combo" truck seeing drag race and possible even track day/autocross road course style racing. For the occasional drive...it can have a "bit less then street manners"...it'll just add more to the fun. My fuel injected vehicles will be the "tame" ones.

[77BBGMC]

Once it's installed get a vid with sound so we can hear it...

[MONTE]

This is what mine sounds like with 3''exhaust
Just sound on it

YouTube - IMG 1198

[v502]

Originally Posted by MONTE

This is what mine sounds like with 3''exhaust
Just sound on it
YouTube - IMG 1198

Thats sounds great what kind of mufflers you got.

[Jacfourteen]

Originally Posted by v502

Thats sounds great what kind of mufflers you got.

X2



Also I'm a little late for the debate but I woulda said 3"

[MONTE]

I think they are trusher's. Got them at a local autopart store.
Posted via Mobile Device

[pharmd]

Another option is to use 3" or 3 1/2" cutouts off the headers (run a short 3 or 3 1/2" pipe from header to cutout), then reduce and run 2.5" out of the cutout. If you have having clearance issues with larger pipe, or if their is a huge difference in pricing (although this setup will cost more in the end). This way you can run quieter mufflers for longer cruises and keep it tolerable, then have an open header type sound when you want to get crazy with cutouts open (the cutouts open will make the most power over any sized exhaust BTW).

Here is an example...

102_5596.flv video by 05pharmd - Photobucket