I wanted to start ordering parts to mod my exhaust. but first i wanted to know a few things. first what size pipe is the stock exhaust system? ive heard that it s 2.5 and im curious on what would happen if i made the pipes 3 inches instead. but so far here is what i want done; plog, downpipe,res delete, muffleres with some nice tips. also, is there a plog for the rear manifold as well. and last but not least im wondering how hard would it be to do all of this work myself, and will i run into any issues like things not fitting and whatnot well looking forward to hear some opinions and ideas from you guys and thanks

 

The rear plog is turbo only specific. Either get a front plog and downpipe or buy headers.

IMO under 300hp get a front plog and down pipe with 2.5" exhaust

Over 300hp headers with 3" exhaust

You do t want a huge exhaust unless you have mods to flow it because it could loose HP if the exhaust is to big for your mods.

 

I agree with Turbo. Our pipes are 2.5".
I'm N/A and I'm running a straight pipe w/no muffler. Sounds so amazing imo. People hear that loud v8 rumble and turn their heads when I start.

The only reason I'm still running stock headers and 2.5" exhaust is because I'm not pushing alot of exhaust gases.

My exhaust setup is done for now :p

 

thanks alot, i dont wanna do major performance gains, rather i am going to get more mpg, thanks for the insight

 

not to sure onn what u meant by not pushing alot of exhaust gases

 

The factory stock exhaust is fairly reasonable with exception to a couple small issues.
The factory downpipe (which includes U-bend) is 2.5" outside diameter. It is double lined steel, so the inside diameter works out to about 2" (I actually cut my stock down pipe open when I swapped it).

The front exhaust manifold is a bit restricted where the back one is a little more flowing (hence the front PLOG).

As for 3", just as John said, if you aren't going to mod to the point of pushing much higher HP, don't go beyond 2.5" for the exhaust.

As for doing it yourself, I see no reason you can't. I swapped my down pipe and PLOG in driveway. Just make sure before you work on it, spray the bolts with penetrating oil (like PB Blaster). Don't be surprised if they snap (luckily mine did not snap).

Here's some info from when I swapped my down pipe:
'04 Monte Carlo SS - ZZP Downpipe

 

if i do decide to do this i hope nothing snaps...i would be screwed, im assuming it took am assortment of different tools to complete? also i seen a video on youtube where the guy had to cut the heat sheild a bit in order for his o2 sensor to fully sit correct did u have to do this as well?

 

What I meat by not enough exhaust flow; I don't have the mods to make alot of exhaust to make the 3" effective.


I had a shop swap my downpipe, u bend and resonator delete, and a flowmaster muffler for $250.


If I had a lift or a means of a way to do it, then I would have done it myself. Sometimes its just better to have a shop do it :p

 

The factory cat-back exhaust on all 6th gen 3.4, 3.8, 3.8 SC and 7th gen 3.5 is 2.25", and 7th gen 3.9 and 5.3 LS4 are 2.5".

If you can find an LS4er needlessly upgrading his cat-back to a Magnaflow (happens all the time) and buy his OE exhaust, it's an upgrade.

Maniac is spot on about the downpipe and front manifold being the most restrictive.

Assuming you have a 3800, I mentioned on another forum that these are mislabelled Grand Am headers but they're actually copies of S&S headers for the Grand Prix, and with their 2.5" collector and smaller primaries they're ideal for non-supercharged 3800s OBX Exhaust Header 99 05 Pontiac Grand Am 3 8L V6 3800 Headers | eBay

 

It really did not take a ton of tools to swap the front mani and the down pipe. You need the correct size socket (deep wells are best) and wrenches (can't remember which sizes, so have, so have 10mm, 13mm and 15mm on hand), a variety of extensions (and a long one is helpful). A jack and jack stands.

I did the PLOG with the Monte on the ground, the down pipe, I raised the car and set it on blocks, but you could also set it on jack stands. When I releases the bolts holding the down pipe and the rear mani together, I was under the car and I reached those bolts with a socket, ratchet and long extension (this way the handle of the ratchet was down where it had space to turn).

Now, I have see the bolts where the down pipe and Y pipe in the back connect have some issues (on a different W-body, I helped change that gasket). The bolts snapped. As a result, the holes had to be drilled out and replaced with nut and bolt setup.

Also, if I might make a recommendation.... When I did my down pipe and PLOG, I wish I took the time to replace the hardware with stainless (instead I used the old hardware, which at the time seemed fine, who knows how it is today).

And lastly, I did not have to cut anything for any of the exhaust pieces or rear O2 to fit. It all just fit.