Starting to modify the 2000 GTP. Suggestions?

**3800SC4DR** · 07-24-2015

So my father is looking to start modifying his 2000 Grand Prix GTP 4 dr. Nothing too crazy, just looking for a little more power.

The car has 87,000 miles. Great shape. When he first got it it had a little problem that we sorted out with the MAF.

So far it has just the resonator deleted (was when he got it), A K&N drop in filter, and we modded the air box. (Took the baffle out, and routed out the holes in the side of the air box. Read a write up somewhere, called the "Whine Box mod".

He already has a ZZP Front Power Log ready and waiting, but also wants other items as well. He'd like to do everything all at once. He's looking at the ZZP Rear Power Log, Ceramic Coated Crossover, 3" Downpipe with Cat, PCM 1.0, Colder Plugs, Lower temp T-Stat, and 3.4 modular pulley kit.

Problem we're having is ZZP doesn't seem to have any of the Ceramic Coated Crossovers in stock. I'm on th email list, but that's been at least a month. Emailed them and they said they don't know when they will be in stock, that they are waiting on cores to be sent out to be coated.

So my question is, are they just stock crossovers that have been coated? Do they do any port work to them? And if no port work is done, is it a vital piece then.

I've read that the rear power log and the crossover aren't that important, but would like some input.

He also wants to modify the exhaust from the cat back, he wants to put a glasspack where the resonator is, then delete the mufflers, and just run pipe to some resonated tips. I'm not sure if this is the optimum way to get good sound, but he seems to think so.

My friend who spends a lot of time with us has an 03 Audi A4 3.0 Quattro 6 speed that he had the mid muffler/resonator deleted and replaced with an x pipe, and the mufflers replaced with straight pipe, and resonated tips put on it. It sounds great. Very exotic sounding and loud. Has a mix between a VR6 and a 350Z tone to it. So I think that's why he wants to put it on his GTP. But I haven't heard many setups that I think sound good on the GTP. I've heard one on a dyno on youtube, but it was turbocharged and it sounded very reminiscent of a Toyota JZ Inline 6 Engine. Most of the other GTP's I've heard sound raspy, and not very "tuned" sounding.

So what's your guys suggestions? I'm trying to convince him to forget the rear power log and crossover and just order the rest of the stuff he wanted, and try to figure out a different exhaust setup. But I'm not a 3800 series expert, so I don't really know what works best.

Oh, and what could he expect power wise from the K&N drop in, air box mod, Front P-Log, 3" downpipe w/ Cat, 3.4 pulley, PCM 1.0, Colder plugs, and Lower temp T-stat?

**Slick2500** · 07-24-2015

For the price you would pay for the rear plog and the crossover you could just buy a set of headers.
As far as I know they are just coated.
As for the exhaust, I would say yes to the glasspack and no to the not running mufflers. Just get on Youtube and watch some vids of what a straight piped GP sounds. It sounds like asshole doesn't it? Do some research on mufflers and find one with a sound you like, Corsa sounds the best imho, but they are also the most expensive.
Also read this http://www.grandprixforums.net/threa...00-Powered-Car!! and take anything you read or hear from ZZP with a grain of salt.

**EHB** · 07-24-2015

since he's already got the plog , get the 3 inch catted or uncatted downpipe. skip the rear plog , even zzp doesn't make claims of any gains. if my rear cracked and needed replaced , i'd get it, but otherwise i wouldn't expect gains. header wrap will do more for the crossover than the ceramic , plus it's a lot cheaper. get the 2.5 , 30 inch thrush GP to replace the resonator.
take a listen to the cherry bomb extreme mufflers. of all the setups i've heard i think it sounds the most aggressive without being obnoxious.

**Slick2500** · 07-24-2015

Cherry bomb lets a lot more rasp get through.

**EHB** · 07-24-2015

Originally Posted by Slick2500

Cherry bomb lets a lot more rasp get through.

actually it doesn't sound bad in the cab in this video. what this guy did was put 1 cherry bomb in place of the Y section. i'd use 2 like normal mufflers.

**Fivefingerdeathpunch** · 07-24-2015

Skip the rear log and just get the 3in downpipe because he already has the front powerlog.

I personally wouldnt touch the exhaust, you/he will hate the drone with most exhausts unless you spend some money. Cherry bomb mufflers will sound terrible and won't sound anything like a Audi just because that is a completely different platform.

I'd even skip the ZZP pcm, they arent very good. Also when modding, it's wise to have somesort of scangauge to monitor the motor. You don't want to be doing things blind but that also means that you'd have to learn how the motor does its thing, how it thinks, how it figures out what is good and what is bad. Knowing engine lingo that deals with timing, engine knock and so on.

**3800SC4DR** · 07-25-2015

So from what I've gathered, forego the rear log and crossover unless they are currently damaged.

Also, to get some sort of scan tool to monitor KR such as the AeroForce Scan Gauge. I'm still trying to convince my father of the importance of getting such an item to monitor KR, and maybe even do a baseline run first to see if he has any KR in stock form. He says "He can't hear any knocking, pinging, or detonation".

He's also under the misconception that you can do just about anything to any engine that's fuel injected, whether it be my 92 C1500 with a 350 TBI such as throwing in a huge cam, or dropping pulley sizes on a GTP and everything will be just fine without a tune because all the computers are self learning and will always maintain a 14.7:1 AF ratio. I know that's definitely not true with my 350 TBI it would run like **** in my C1500 which is why I'm in the process of swapping it to a carb. I'm assuming the same is true for the GTP in regards to dropping pulley sizes and increasing boost. A friend of mine has a WRX that he went from a top mount to front mount IC, put an external wastegate and screamer pipe on it, and increased the boost, and until he got his tune right it ran like absolute dump.

I did read over the FAQ regarding modding the GTP, but noticed that it was written in 2009. It's now 2015.

In regards to the PCM, who would you recommend for the planned mods? Is it still Overkill Motorsports, 3800 Performance, or Reptile?

Appreciate all the help, would rather do this right the first time.

**Reptile** · 07-25-2015

I can absolutely give you a hand on the PCM.

**SgtMarshal** · 07-25-2015

I would mention to him that even from the factory these car have detonation. a typical stock GTP will has about 4* of kr at full throttle. tuning will make a huge difference on these cars because the transmission shift settings are slow, the transmission doesn't shift down from 4 to 2, and when you install the ported exhaust manifold, downpipe and smaller pulley you will have more air flow so you can increase timing advance to maximize the gains. as far as maintaining the stoichiometric 14.7, that is not necessarily a good thing, because under power enrichment you want a much richer afr such as 11, and I think the oem pcm doesn't command that.

Having an aeroforce scan gauge will help with other things as well, such as monitoring long term fuel trims and boost levels. another risk about not knowing how much kr you have is associated with dropping pulleys. because every engine is different and every engine responds to modding differently, you need to know how much kr you have so you can put a bigger pulley on if there is too much kr. These cars dont actually start knocking until it is too late, so the sound your father is looking for is the sound he may hear if the kr monitoring solution is not heeded.

**Slick2500** · 07-25-2015

Originally Posted by 3800SC4DR

So from what I've gathered, forego the rear log and crossover unless they are currently damaged.

Also, to get some sort of scan tool to monitor KR such as the AeroForce Scan Gauge. I'm still trying to convince my father of the importance of getting such an item to monitor KR, and maybe even do a baseline run first to see if he has any KR in stock form. He says "He can't hear any knocking, pinging, or detonation".

He's also under the misconception that you can do just about anything to any engine that's fuel injected, whether it be my 92 C1500 with a 350 TBI such as throwing in a huge cam, or dropping pulley sizes on a GTP and everything will be just fine without a tune because all the computers are self learning and will always maintain a 14.7:1 AF ratio. I know that's definitely not true with my 350 TBI it would run like **** in my C1500 which is why I'm in the process of swapping it to a carb. I'm assuming the same is true for the GTP in regards to dropping pulley sizes and increasing boost. A friend of mine has a WRX that he went from a top mount to front mount IC, put an external wastegate and screamer pipe on it, and increased the boost, and until he got his tune right it ran like absolute dump.

I did read over the FAQ regarding modding the GTP, but noticed that it was written in 2009. It's now 2015.

In regards to the PCM, who would you recommend for the planned mods? Is it still Overkill Motorsports, 3800 Performance, or Reptile?

Appreciate all the help, would rather do this right the first time.

That is when he originally posted it, he has been keeping it up to date, and he is actually getting ready to do another update on it.

Sent from A Galaxy Far Far Away

**blueguy** · 07-25-2015

That thread is still worlds ahead of any vendor recommendations in the 3800 community.

Don't over think it.

**3800SC4DR** · 07-31-2015

Just had the front p log installed.

Did a scan, 0 degrees of KR. 22 degrees total advance timing.

Small leak coming from crossover, but not terrible.