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GXP Exhaust. Ordering parts but have questions

DirtDog

DirtDog

New member
ok so heres what im fixing to order for sure. My intentions with my exhaust are to make it a little louder and allow the engine to flow better as im pretty sure the stock restricts it alot.

zzpdownpipe_zps5338f902.png



so a the first of my exhaust questions to come is the exhaust pipe the runs from the DP to the Y split is 2.5" (im pretty sure) then from the Y split it goes down to 2" to the mufflers. now with the new DP will i need to replace all the exhaust pipe to a larger size? like the same size as the DP, or should i use this and not get an 02 bung on the DP and use the one on this

DPreducer_zpsc60af984.png


I am also going to do a resonator delete and straight pipe that section. for mufflers i am not completely for sure where to start on these...so many different types. like the offset and where the inlet and outlet is located. Would this one work and sound good?

Flowmaster 40 Series™ Delta Flow 942041 - Muffler | O'Reilly Auto Parts
edit: flowmasters....rulled out for now looking for something better thats not as crappy.

now for the type of tips i should get...i dont want expensive and i also dont mind to have to clean them every now and then. but i know im going to have to replace the stock ones so if anyone has any suggestions or ones for sale please let me know.

any other exhaust stuff or links i should read as well let me know. ive been reading alot of em on here but none have good specifics that im looking for so i can order
 
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The donwpipe should bolt straight up to the factory cat-back.

Are you planning on running a cat? How are you going to deal with a code if you don't run one?

For mufflers, get under your car and see where the pipe enters the rear of the muffler, that will tell you what offset you will need to buy.
 
i was going to run a cat less DP. what difference performance wise does the CAT have? if no difference i was gonna have it tuned out when i do a tune. i am going to have DOHCZ3 do a custom tune for me within the next couple months. I have to buy a new PCM though cause my 06 cant be reflashed or something like that
 
Performance difference is none.

Gas Mileage difference is something you will see without a cat and no tune. The code P0420 will set and cause the car to use extra fuel to see if it can get the rear o2 to read what it wants, but it never can. So with a tune, it can be worked around.
 
Hmmm I may add the CAT to the zzp DP cause it probably won't be until march time frame when I'm ready for him to start tuning. What about the pipe from the DP to the tips? Will I be fine leaving all that stock sizes except for removing resonator and changing mufflers and tips?

edit: i just updated the original post up there and added the CAT in to the DP.
also what about the exhaust reducer that zzp has listed i posted up there
 
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I would leave it all the same size and just have the mufflers cut and welded on there. They really is no reason to replace the whole exhaust because you dont gain anything.
 


and that makes since. for tips what should i do? on the stock ones this inside is like a 1" or 1.5" im not forsure but their tiny compared to some of the dual aftermarket ones ive been looking at.
 
is flowmaster better then magnaflow? or are they one in the same? i'm looking to put a different exhaust on my GXP too in the near future.
 
sorry this kinda jacks the thread but thought i'd ask since we have some GXP guys here. i was looking.. GXPs only have one front engine mount? is that good or bad, as in does that single one get the job done or why is there only one instead of having two.
 
Why not just invest in a set of headers. Doug Thorley offers a set. I also believe Cal Speed Perfomance is making a set. There is plenty of info over at ls1tech.
 


The headers for these cars are way over prices and for the money just don't do enpugh. But please let's keep on topic here from my original post. As for the engine mount question...it still has two.

Sent from my pager using Morse code. ... .. ... ....
 
but one of the mounts is different from the 3.8. as seen here
Search for 'engine mount' - 2006 Pontiac Grand Prix | O'Reilly Auto Parts
click show all when the link loads.

As for flowmaster over magnaflow or any other muffler im not forsure yet. i havent ordered mine and am still looking around and gathering info on which ones i wanna go with.

http://www.grandprixforums.net/mixed-emotions-about-exhuast-mufflers-72154.html
that link is another recent thread on mufflers that ive been following.

theres several other threads to just not gonna take the time to post. i cant seem to find a definite answer as to what the best type of muffler is sound wise for the gxp's but im probably gonna order some soon if no one else has any input. ill let ya know which ones i order, how they sound, and maybe even post you a video if im feeling lucky
 
None of the mufflers will make the sound you are looking for. The crossover design makes it sound the way it does. The Flowmaster 40 series is going to be loud and cause drone inside the cabin.
 
yea i was actually just reading on the flowmasters 40 reviews and alot say they drone bad. this is the ls4 engine so it will sound alot better than the 3.8. i also dont want to spend a ton of money on mufflers. but i do want the car to be a little louder. i dont mind a little more noise inside the car either and havent decided weather or not to replace resonator with glass pack yet or straight pipe it. some people say straight piping it makes it worse. what types of mufflers should i look into? design wise that is. chambered or not...bends

what about this brand
Dynomax® Performance Exhaust | Mufflers | Ultra Flo™ SS Polished Mufflers
 


hmmm i dont want it super loud. but i want it more noticeable. from what ive read the exhaust on the gxp's restrict flow a lot. how much louder is a cutout and does it make any performance gains? i do know for sure that i'm going to do a new ZZP DP.
 
Personally I would get Magnaflows for the Gxp...Flowmasters 40s are just to loud and drone like crazy. Magnaflows will increase your tone slightly compared to stock.

If its a 3800 = Borla. LS = Magnaflows.
 
marines542 said:
hmmm i dont want it super loud. but i want it more noticeable. from what ive read the exhaust on the gxp's restrict flow a lot. how much louder is a cutout and does it make any performance gains? i do know for sure that i'm going to do a new ZZP DP.
Click to expand...

Yes a cutout will be loud, but the benefit is being able to close it when you factory sound. As far as performance it will be like running open headers so there is a gain there especially when it comes to a LS based engine. You are only talking about maybe spending 50ish dollars with install. So it's not like you are losing a whole lot if you decide you don't like it.
 
contrary to belief we do have gains with the cat back for the LS4's GXP cat backs are restrictive and tiny. when i had mine chopped apart you wouldnt believe how tiny the ubend and tips are especially. i posted alot of pics under the ls4 section on ls1tech about it. i have the hogan catless DP and full 3' exhaust to a split 2.5 out. but anyway heres the magnaflow dyno link MagnaFlow Cat-Back Grand Prix GXP 16726 - PFYC.com

and to answer the motor mount question we dont use the same 3800 lower engine mount. we have two one in front of the oil pan one behind the passenger side cv axle and the one we share with the 3800 guys are the upper dog bone and driver side trans mount
 
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