2.5 or 3 inch exhaust???

**timboku** · 03-26-2014

Going to be upgrading exhaust. Got a gen v top swapped l26 in a 02 gtp. Going to go full size intercooler. Have SD headers and a bunch of other stuff but not CAM yet. Should I get a 3 inch. Heard different stories its better to run the stock size unless turbo? I hate drone so dont know if the 3 inch will add more but looking at a 30" glass pack, no cat, and dynomax vt mufflers to help with the drone (mixed reviews on these as well but they are 70 bucks on ebay and seem decent). 3 inch is only a little more money so if its benificial for my set up I will get that, if not I will stick with stock size.

**Sven the Sexman** · 03-26-2014

2.5 inch exhaust is more than adequate for what you have planned. Going 3 inch will probably cost you a little down low, but it will make up for it in the higher RPM when you really need the flow. I ran the GMPP exhaust (2.5") on my car Gen V, IC'ed, XP cam, mildly ported heads, 3.0 pulley (typically left the 3.4 on,) and SLP headers.

**timboku** · 03-26-2014

Cool thanks thats what I thought.

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**Sven the Sexman** · 03-26-2014

No problem. Have you decided what you're doing for heads/cam yet?

**timboku** · 03-26-2014

No thats on the block.for.next year..gotta a north star, ic, 42.5s to.put on when weather warms up...I have 1.9s on it now but was looking at xp cams and idk about heads but they will be next year to.

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**Sven the Sexman** · 03-26-2014

My recommendation is as you're thinking of upgrading, figure out where you want your car to be powerwise. Once you have that, then you can ask for suggestions to get there.

**timboku** · 03-26-2014

For sure..idk how far I will go..its kinds of a dd but I have a gxp as well that I like that is stock so I can keep on building up the 02...big thing is if I want to get a built trans which if I keep.going will have to happen. If I invest in a trans.then.it could turn.into a.nice build. But we will see.

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**Sven the Sexman** · 03-26-2014

Talk to GMR Badass about your trans needs and he'll be able to point you in the right direction with that. If you are after anything over 300WHP, time to think if SC is the right path for you...because you could unload all your stuff and basically get a turbo kit that'll put you there by bolting it on.

**coolone** · 03-26-2014

Although the 3" may be more than you're needing, it won't cost on low end. I run pacesetters, with 3" to mufflers and my low end is just fine. But then again, I opened up the intake too, ported SC and TB along with 1.9 YT RR's on. 3.4 pulley.

I would just recommend trying to know what you're going to do with the engine, how far you plan to take it. The 3" may be fine then.

**Bio248** · 03-26-2014

you really don't need anymore than a 2" catback until you're over 300whp...

**timboku** · 03-26-2014

The.plan is to put full size ic on and drop to 3.1 to 3.0 pully. north star, 42.5 injectors..waiting to go.on...I.want to.cam it and do heads next year and then we will see...with a cam and those mods will I be close to 300whp? Im.not sure

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**timboku** · 03-26-2014

Also.have headers.and 1.9s on it.now..obviosly 1.9s go away with cam and heads.

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**Bio248** · 03-26-2014

you'll be over it if you follow through, but there's still no need to go any bigger than a 2.5" exhaust.

3"+ exhaust is for turbo cars.

**timboku** · 03-26-2014

Perfect thanks!

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**Overkill** · 03-29-2014

Nonsense to most of the above; if you're spending money on an exhaust system for a supercharged 3800, always go 3".

**SnowFlake** · 03-29-2014

After seeing over and over and over how restrictive the stock exhaust actually is... go 3" every time no matter what your setup is lol. Bigger on the front end if you can fit it!

**timboku** · 03-29-2014

Alright gonna go with the 3 inch since I will more than likely continue to build the car...gonna go.with the mandrel exhaust system they have a 3 inch for 275 shipped...they can weld in a dynomax resonator for 75 bucks more. Is that a good resonator? I was gonna have 30 inch glass pack welded in and it would be only about 20 bucks more to have them just weld the dynomax in by the time I purchase the glass pack and have a shop weld it in.. just wondering if its worth it and will it sound good. Its only an 18 inch resonator.

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**Overkill** · 03-30-2014

Magnaflow 12641 muffler is what I recommend using as a resonator in a 3" system. Combine with the mufflers of your choice or run straight pipes at the back if you want it loud but minimal drone.

I like your choice of Dynomax VT mufflers, I'm becoming a believer in their benefit. If you buy the ZZP system (just the piping), keep in mind they switch to center inlet mufflers, and VTs aren't again in center inlet/outlet that I'm aware of, so you'll need to have the pipes modified for offset in and center out, straight forward to do.

On the 2.5" vs 3" debate, a long time ago a customer of mine had a Trash-er intake, 3.4 pulley, TOG headers and when installing he ran 3" piping through the resonator area before continuing the stock exhaust around the tank and to the stock mufflers. When he had his single 3" system continued around the tank and finished into dual Magnaflow mufflers, he dropped 1psi of boost and was able to drop to a 3.25" pulley. That was a basic modified GTP, and a 3" system dropped 1psi of boost, eliminated that much restriction. That's why I've always recommended since that if you do headers, do a 3" system, no matter the extent of your other modifications, you'll be doing the right thing.

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