exhaust size 2 1/2 or 3 inch

[thumper877]

Got my new ls3 525 hp for performance end what size exhaust is best I have heard small blocks like the smaller for the back pressure. Not sure if the ls is different. I'm usually a big block guy so any help or advice would be great thanks

[andrewb70]

I think 2.5" exhaust is good for up to 600hp. It also saves weight.

Andrew

[thumper877]

Thanks Andrew

[icemanrd19]

I installed a 2.5 dynatech exhaust. from headers back a 3" would work fine but with my quadralink i wouldn't want to deal with a 3" tailpipe.

I highly recommend dyatech muscle max 2.5" exhaust. Great fitment.

[thumper877]

Thanks randy I will check into that

[rohrt]

Jim Hand in the pontiac world did some extensive testing on exhaust systems. Based on the exhaust cooling and back pressure measured going 3" to the muffler and 2.5 for the tail pipes may be the best of both worlds.

[LS6 Tommy]

Jim Hand in the pontiac world did some extensive testing on exhaust systems. Based on the exhaust cooling and back pressure measured going 3" to the muffler and 2.5 for the tail pipes may be the best of both worlds.

Jim used Torque Technologies stuff. I'ved used them before, too. Going with them again on Madge. Good guys!

Tommy

[1989GTA]

Jim Hand in the pontiac world did some extensive testing on exhaust systems. Based on the exhaust cooling and back pressure measured going 3" to the muffler and 2.5 for the tail pipes may be the best of both worlds.

That is what I would think.

[icemanrd19]

[camarodude87]

Ice, just curious if those are corsa mufflers?

[72BBSwinger]

3" from headers and mufflers and 2.5" tails.

[thumper877]

Wow randy that's a nice looking exhaust tucks in there and gives u some good ground clearance to what type of headers u running and subframe

[icemanrd19]

ls3 with stainless works headers and dse front clip

[67SSDan]

So I've always associated a stepped down pipe size (3 in > muffler > 2.5 in) with the old farty truck exhaust sound. Guess that's not the case? Have been thinking about this very question myself.

Dan

[TomsResto]

Probably too late to be of any help to thumper877 but I'll share in case anyone else stumbles on this thread (like I did while flipping around the forum over lunch break)

Reminded me of an episode of engine masters/roadkill that did some comparisons of 2.5", 3" and open headers including weight of all component,etc.

In this case for an engine putting out more than 600H.P. the 3" exhaust produced more horse and they think debunks the backpressure claims... some quick google/youtube searches and here it is:
https://www.youtube.com/watch?v=_PVXvHkr-Vs

[rohrt]

Probably too late to be of any help to thumper877 but I'll share in case anyone else stumbles on this thread (like I did while flipping around the forum over lunch break)

Reminded me of an episode of engine masters/roadkill that did some comparisons of 2.5", 3" and open headers including weight of all component,etc.

In this case for an engine putting out more than 600H.P. the 3" exhaust produced more horse and they think debunks the backpressure claims... some quick google/youtube searches and here it is:
https://www.youtube.com/watch?v=_PVXvHkr-Vs

Nice video. To bad they couldn't keep going with more testing like a X-cross over of tried a mix of 3" and 2.5 tails.

Since you posted that for edification I thought I would post the JH muffler test.
http://www.pontiacstreetperformance....p/exhaust.html

[rhurley]

I always go big. 3" on all my rides. sounds better and i have yet to ever find it be negative.

[TheJDMan]

The only negative I can see to 3" exhaust might be packaging.

[68Formula]

With that combination of displacement vs. peak power, you could go a couple ways.

- 3" mandrel bent from collectors with x-pipe into 3" mufflers out to 2.5" tailpipes
- Same as above, except 2.5" collector back through x-pipe, mufflers and tailpipes

The relatively small displacement (compared to big blocks) vs. high horsepower, will probably show a low to midrange torque advantage if you go 2.5" all the way. While the 3" down to 2.5" tails would free up a few ponies on the top end at the cost of some low to midrange.

Also important, research your mufflers to ensure they're providing peak efficiency. Loud is not always best flow (one of the most popular brand of loud mufflers are actually horribly inefficient). Not much point of putting 3" pipes up front if you're going to choke it with mufflers that flow less than 70% (compared to a straight through pipe).

So it's down to what is more important to you, and what you can package. Either way, make sure it's mandrel bent, includes the x-pipe, and keep the tails 2.5".