Thread: Starting to mod my GXP - help me.

Well its income tax time and I got some decent money coming back to me. My 2005 Grand Prix GXP is in storeage and is screaming to get some work done. I need a few questions answered.

First off I am going to be doing the exhaust. Looking at putting on a highflow cat. However I was wondering what is the factory catalytic convertor input size? I want to do a 3" cat back. into 2 Flowmaster Super 40s.

Second is there any cheaper intakes than the K&N that has proven to be a good mod for the GXP? With the K&N intake does it have a tray for the PCM to be bolted down? I dont want to zip tie the PCM down or cut apart my factory airbox.

Third is a Thottle Body spacer going to give me any noticeable difference or benefit me? I see some people saying do it, and some saying its a waste of $100.

Also Ive been hearing a lot about flipping a motor mount or changing the mounts? Any suggestions on this while Im working on it?

Last where is my best bet to send in my PCM in for a tune? Ive thought about a handheld but not so sure on it...

look here for answers

Grand Prixs Of North America • View forum - GXP Area

No such thing as modding a GXP, and yes the k&n has a mount for the pcm if im not mistaken. And 40's are too mellow, 10's ftw.

a spacer probably won't do much. really all i've heard about it is that i cuts off coolant to the rear bank, and that's not good. if you wanna go fast, cam it. but that's just me

go turbo

Originally Posted by tod1d

go turbo

Go built transmission first.

do a cam and down pipe or headers tune a cone filter done then when the tranny blows get a tep

Originally Posted by extreme

Well its income tax time and I got some decent money coming back to me. My 2005 Grand Prix GXP is in storeage and is screaming to get some work done. I need a few questions answered.

First off I am going to be doing the exhaust. Looking at putting on a highflow cat. However I was wondering what is the factory catalytic convertor input size? I want to do a 3" cat back. into 2 Flowmaster Super 40s.

Factory converter size is probably either 2.25" or 2.5"...I however recommend a Curt Hogan bolt in catted downpipe that is 3"...see that one here: DP7S

Great guy to do business with as well. 3" catback is probably over kill...if you get the downpipe, I'd say a Magnaflow or SLP Loudmouth would be great additions and I hear nothing but great things from the GXP owners who spent the coin on a Maganflow system. I've installed a Magnaflow catback on my lady's G5 GT and when my old man bought his new 2011 'Stang...we got a Magnaflow Competition kit for it as well. Great products and easily installed with jackstands and simple hand tools.

Something to keep in mind...Flowmaster mufflers are very loud...and if you plan on doing a good portion of highway cruising...they drone pretty bad. Food for thought.

Originally Posted by extreme

Second is there any cheaper intakes than the K&N that has proven to be a good mod for the GXP? With the K&N intake does it have a tray for the PCM to be bolted down? I dont want to zip tie the PCM down or cut apart my factory airbox.

Cheaper? You can always make your own intake...OR...even though I have heard nothing BAD about K&N's kit from the GXP crowd, this one is WAY better and comes with a PCM tray that you were worried about...

Pontiac Grand Prix GXP 2006 - CAI Air Intake System

Originally Posted by extreme

Third is a Thottle Body spacer going to give me any noticeable difference or benefit me? I see some people saying do it, and some saying its a waste of $100

Waste of money IMO. Will it HURT you...probably not on an N/A V8 car...but it isn't worth the coin.

Originally Posted by extreme

Also Ive been hearing a lot about flipping a motor mount or changing the mounts? Any suggestions on this while Im working on it?

In the link in my signature...click the one about mods. OR...click the other one if you just want to hear a big, lopey, cammed, 3800

One of the first things in that thread discusses however, is the dog bone flip...the 3800 powered WBody's have the same dog bone. It is very easy to do...You can also email ZZPerformance or Intense-Racing to see if they can just ship you half of an order since the LS4 cars only have 1 dog bone.

Originally Posted by extreme

Last where is my best bet to send in my PCM in for a tune? Ive thought about a handheld but not so sure on it...

Handheld tuner's don't work very well on these cars...I'd say your best bet it is finding a local that can tune with HP Tuners.

Overkill PCM for your GXP :: Overkill Motorsports ::

I'd look into a Hogan downpipe, ask if it can be made with a 3" exit, and then get a ZZP 3" cat-back with or without mufflers if you want to use a specific brand of muffler.

For the intake, a drop-in K&N or other panel filter plus some minor modification to enlarge the inlet will be highly effective and save you a few hundred dollars. If you want to buy a ready made, buy on asthetics, cause that's what you're paying for.

save up and get a turbo kit.

YouTube - Turbo GXP at the Dyno

that said theres barely any aftermarket for the gxp's that i know off. a cai, dp and a pcm would be a good start if youre on a budget and dont know how far ur going to go.

http://www.grandprixforums.net/v8-guys-39266.html

I like the CAI box. With a little aluminum tape around the edges, you can see a difference in IATs. I picked up a kPa or two at WOT as well. Skip the spacer. It might help by slightly increasing plenum volume and giving air a chance to straighten a bit before the restriction in the throttle neck, but more than likely it will just kink the induction tract and throw the MAF transfer off. You won't need a 3" exhaust unless you've done a lot more to your car, but if you plan to do more it can't hurt to get it now.

LS4 sir. but good info

Originally Posted by 007

If you still have the factory cat(s) and are selling them, don't let nebrs13 (Christian Acton) rip you off -he's a forum leach and will offer you less than 1/4 f what anything is worth.

That aside, a high flow exhaust, a good intake setup, along with any aftermarket RWD LSx power mods that can be adapted easily to the LS3 powered W-bodies will help you along, but be VERY aware that your transmission had trouble handling stock 3800 supercharged power so with the power of the LS3 V8 it is very common to see them fail by 60,000 miles, and if it doesn't there, most will fail by 100,000 and the added stress from adding HP and torque will only cause it to fail even sooner.

LS4...LS3 is quite different.

Also, the bashing of another member isn't allowed...take that junk elsewhere.

Originally Posted by extreme

Well its income tax time and I got some decent money coming back to me. My 2005 Grand Prix GXP is in storeage and is screaming to get some work done. I need a few questions answered.

First off I am going to be doing the exhaust. Looking at putting on a highflow cat. However I was wondering what is the factory catalytic convertor input size? I want to do a 3" cat back. into 2 Flowmaster Super 40s.

Second is there any cheaper intakes than the K&N that has proven to be a good mod for the GXP? With the K&N intake does it have a tray for the PCM to be bolted down? I dont want to zip tie the PCM down or cut apart my factory airbox.

Third is a Thottle Body spacer going to give me any noticeable difference or benefit me? I see some people saying do it, and some saying its a waste of $100.

Also Ive been hearing a lot about flipping a motor mount or changing the mounts? Any suggestions on this while Im working on it?

Last where is my best bet to send in my PCM in for a tune? Ive thought about a handheld but not so sure on it...

http://www.diablewtune.com/

Cartuning Performance