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04 GTP questions, seeking mod advice



blueguy91 said:
I'd recommend exhaust work on ANY 3800...of any level of modding.

It's god awful. The catback is fine; but everything else needs help. Manifold casting is crap, the downpipe is tiny, and the U-Bend is even worse.

On a stock car, PEM's and a 3" downpipe would probably add 15-20~ horse...and most of that would just be killing all the KR.
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I have been trying to figure out how much it would cost me to do headers, but I'm starting to see that I might have major issues passing emissions inspections here if I go that route. I would pretty much have to run a stock catalytic converter to avoid setting a code, and ANY code thrown during the emissions inspection here will fail the test (even if it's not emissions related!). And you can't have the codes deleted or emulated, because they actually do an OBDII test that basically checks to see if the PCM has been coded to ignore emissions DTCs or anything else to get around emissions.

So now I'm considering 1.9 rockers and a good tune, but it seems a shame to leave the stock exhaust system in place. Maybe I could have an exhaust shop here build something for me? Might be too expensive for me though.
 
TheTokenAsian said:
I had similar KR on my car, bone stock except shift kit. ZZP plogs + their 3" dp dropped it down to < 2'. The 180 thermostat didn't really seem to help KR on my car nor did 1 range colder plugs. I'm considering getting their 1.9 rockers today since they're on sale to try to eliminate KR entirely, but not sure if it's worth it.
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Did you install the downpipe and plogs at the same time? If not, did one help more than the other? I'm wondering if the front plog or downpipe would help more since 04+ cars don't have the downpipe u-bend and therefore might not be as restrictive.
 
you can still run headers or a downpipe with a catalytic converter and keep all the emissions intact. are you sure Utah county checks for emissions like that? I would be interested to see how their check can actually see if emissions have been tampered with. Even if you get a tuner and tune the vehicle, there are still gains to be had if you keep the emissions.
 
here in NJ they "look" for your cat, and obd scan for codes. i got a 50 dollar hi flow cat welded in. you can have a shop do that. as well as move the o2 bung. sd headers have a mid pipe in the down pipe, remove that pipe install the cat in its place. easy. you could band clamp the cat in place if need be. i did to get through inspection.

you need a tune with the cat and rear o2 deleted and you'll pass no problem.
 
cat band clamped in with rtv. passed NJ inspection. they dont go easy on you here.......still passed.

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SgtMarshal said:
you can still run headers or a downpipe with a catalytic converter and keep all the emissions intact. are you sure Utah county checks for emissions like that? I would be interested to see how their check can actually see if emissions have been tampered with. Even if you get a tuner and tune the vehicle, there are still gains to be had if you keep the emissions.
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I looked up the actual Utah county code on emissions and it says this:

"The mechanic shall:

"On 1996 and newer vehicles, fail the OBDII system tampering inspection if it is determined that the vehicle computer has been reprogrammed to defeat the factory OBDII system. This includes, but is not limited to, reprogramming to ignore readiness monitors, hard coding readiness monitor status, ignoring DTC's or reporting false information to the emissions analyzer."

So I'm assuming their analyzer has some way to check for these things. I figure as long as I can get a cat that will function well enough to keep my O2 sensor happy, I can do headers, but I don't know if your typical high-flow cat would cut it. That's why I'm thinking I might go to an exhaust shop around here and ask them what I'd have to do to pass emissions.
 
dont think they can tell one way or another if codes are deleted. they scan to see if items are "ready" or not. if items are not ready you fail.

when you delete codes in a tune they show ready asap and always.

i must have at least 24 codes deleted in my tune, evap, egr, rear 02, and cat codes all deleted.
 
I know at least one person that runs SD headers and lives in SLC, not sure if he is catless or not, but I would suspect that he does have a catalytic converter, so either he deleted the codes or his catalytic converter works good enough.
 
That's good to know. I have 10 months until my emissions are due again, so I guess I'll probably do headers with a high-flow cat and then delete any codes later when I have the means to do some tuning.
 
SgtMarshal said:
I know at least one person that runs SD headers and lives in SLC, not sure if he is catless or not, but I would suspect that he does have a catalytic converter, so either he deleted the codes or his catalytic converter works good enough.
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A cheap hi flow cat or a "test pipe" is the way to go if your e testing is an OBD2 check and visual inspection for the cat, a quality hi flow converter is only needed if you need to pass a sniffer test. I had to install a good magna flow HM (high metal content) on my gtp to pass the sniffer before OBD2 check only came in to effect in my area, a universal or cheap hi flow just won't get the job done compared to a stock cat.
 


I ran an o2 sim for years with no problems with headers and high flow cat.

Don’t have to worry about emissions anymore, 12 years and old no longer require emissions testing in Massachusetts
 
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