Thread: Need Help 2003 Grand prix GT N/A Mods

I'm still learning about these 3800 and they are pretty interesting being that I know aton about the duramax engine but these little engines are starting to lend there power potential to my curiousity. It doesn't seem like it takes near the money to have a fun grand prix as it does to mod a diesel heavly. I'm currently looking to do some mods to my girl friends car and need input on how the simple parts will return to me my investment in them. I'm looking to keep the car N/A so its minor mods I'm looking to do they consist of a ZZ Perf 1.0 pcm upgrade, a ZZ Perf throttle body spacer, a ZZ Perf ceramic coated crossover pipe, and then I'm looking to do as cheap as possible exhuast upgrade to help expel the gases without losing the cat or setting codes. I'm looking to stay as far under 500 bucks as I can but if it takes it not break the limit I have set to spend. so please help me out here as I'm still learning. Thanks in advance

Skip the TB spacer and crossover pipe. They wont help.

For exhaust the best route without going headers, is a PLOG and 3in downpipe. Also note that the highflow cat that ZZP has with their DP will likely set the SES light because its flowing too well for what the car wants. I would cut the cat off your original downpipe and weld it in the 3in downpipe (meaning buy the offroad 3in dp without cat).


I'll leave the pcm tune up to you, I don't see a need for it with what you want to do.

Intake, plog, 3in dp and tune. Right around $500 right there and a good 25ish hp gain.

Please explain this plog to me. Tune is for the 185* fan kick on, shifts, and whatever else I forgot to mention it does lol. Know of a better tuner please enlighten me if they offer prices like zz. CAI already done. Can the tuning take care of the SES lights if I run the 3in downpipe with hi flow cat? Sorry just trying to make sure I understand thing before I order.

Ok so went and checked out PLOG seen it before but didn't notice it called PLOG which ment power log basically a front header. got that figured out. Now on to the 3in Downpipe will it be ok with stock exhaust will it reduce back down to stock size pipe?

Originally Posted by Robby Avery

I'm still learning about these 3800 and they are pretty interesting being that I know aton about the duramax engine but these little engines are starting to lend there power potential to my curiousity. It doesn't seem like it takes near the money to have a fun grand prix as it does to mod a diesel heavly. I'm currently looking to do some mods to my girl friends car and need input on how the simple parts will return to me my investment in them. I'm looking to keep the car N/A so its minor mods I'm looking to do they consist of a ZZ Perf 1.0 pcm upgrade, a ZZ Perf throttle body spacer, a ZZ Perf ceramic coated crossover pipe, and then I'm looking to do as cheap as possible exhuast upgrade to help expel the gases without losing the cat or setting codes. I'm looking to stay as far under 500 bucks as I can but if it takes it not break the limit I have set to spend. so please help me out here as I'm still learning. Thanks in advance

Don't you wish it was as easy as a strait pipe, cai, lift pump, and a efi live tune and voila, 500-530 rwhp? Not quite that easy with these cars haha.

As for mods do headers, open cone type intake (do it for 50 bucks simple and easy), and overkill Pcm. Borla mufflers are preferred for our cars but I myself prefer the stockers. I'm pretty sure your can get headers with the cat. Properly tuned you should have no codes. That should be well within you price range. $200 for headers $165 for Pcm and $50-60 for homemade intake.

Unless you want to lose some of your low end torque stick with a plog, a 2.5" downpipe and not headers. The 3" is not needed on a n/a set up and can result in power lose.

Intake, hv3,tune and you'll be on your way.

Just make sure the flange on the PLOG is welded on properly unlike mine that has caused me so many headaches.

i got HAI,HV3,2.5'' downpipe,91 Octane Overkill Incar tune and as it was a good boost in power I still only netted 15.6 in the qtr mile, im planning on plog and rockers one day but in the end it will be 14.9-15.0 in the qtr.
If you want more power then that you have to boost.

PLOG and rockers aren't going to knock more than half a second off the quarter, just an FYI.

Especially ER Rockers.

Maybe a couple tenths at best...high 14's is what my buddy ran in his rusted out GT2 cammed 3800 SE...it made 202~ WHP with PEM's and a full single outlet 3" exhaust.

Modding an N/A car won't net much gains at all...proven.

Meh true, I never ran thru the 1/4 mile but I did do a 9.4 thru the 1/8th on my old GT build. Had Er rockers,overkill tune etc. pretty quick car but nothing compared to my now lightly modded GTP. Much more torquey

Originally Posted by dazedandconfused

Don't you wish it was as easy as a strait pipe, cai, lift pump, and a efi live tune and voila, 500-530 rwhp? Not quite that easy with these cars haha.

As for mods do headers, open cone type intake (do it for 50 bucks simple and easy), and overkill Pcm. Borla mufflers are preferred for our cars but I myself prefer the stockers. I'm pretty sure your can get headers with the cat. Properly tuned you should have no codes. That should be well within you price range. $200 for headers $165 for Pcm and $50-60 for homemade intake.

LOL yes if it was that easy there would be all sorts of bad grand prix out there. I know gas and NA is a whole different animal just would like to do some decent mods to make the car more fun and reliable.

Originally Posted by REDCOMPG

Unless you want to lose some of your low end torque stick with a plog, a 2.5" downpipe and not headers. The 3" is not needed on a n/a set up and can result in power lose.

Intake, hv3,tune and you'll be on your way.

Intake Check, Tune not yet, Whats this HV3 you and a couple other have spoke of? Explain please thanks

HV3 is an upper intake manifold insert sold by ZZP. You pull out the stock manifold runners and replace it with the HV3. It basically moves the powerband up.

Originally Posted by Robby Avery

Please explain this plog to me. Tune is for the 185* fan kick on, shifts, and whatever else I forgot to mention it does lol. Know of a better tuner please enlighten me if they offer prices like zz. CAI already done. Can the tuning take care of the SES lights if I run the 3in downpipe with hi flow cat? Sorry just trying to make sure I understand thing before I order.

Running a hi-flow CAT will cause a P0420 code to be thrown. This code can be tuned out.