It seems recently that my 05 Base is WAY slower then my 06 Base. It alsmost feels like the 05 hesitates when giving it gas. It is so weird. What could be causes for this? I put dual factory exhaust on my 05. The 05 also has 18"s on it. Which i know they weigh more, but i didnt think THAT much more lol. Could the dual exhaust maybe not be giving it enough back pressure? Do you thing putting a cold air intake on it would let it breathe better?


Edit: So now it gets interesting. I just put a factory dual exhaust on my 06.....and now it feels just like my 05!! It now feels slower acceleration and seems to "hesitate" at low rpm just like my 05. Seems like torque isnt available till higher rpms??? I just don't understand this. I don't see how switching to dual could affect the performace THAT bad?? It technically isn't any less back pressure is it? Although it does have a different smaller resonator then the single exhaust that might be reducing backpressure????

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

^I dont suppose either are tuned, right? Stock PCMs? I would say, just speculation, that it could have something to do with the torque management settings in the PCM or it may have something to do with the 18's you have on there(<not trying to be a smartass). iirc for every 100lbs you add(or take away) to a car it equates to a tenth of a second slower(or faster) in the 1/4 mile

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2005 Pontiac Grand Prix:|SE front|SPO grilles|HPTuned|HUD added|5-button DIC swap|Wizaired CAI|180*|EGR delete|GMPP rear sway|F&R STBs w/DRs brackets|3.29s|HD Diff|7/8" chain|WBS TA's|SD Headers|GenV SSM90 Hybrid(INSTALL PENDING)

yes all stock. I have been thinking about getting a pcm

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

yeah, get a CAI on that thing. the stock airbox is very restrictive!!!

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'07 GP Base SD Headers - hv3 - open cone - HPTUNERS user

How do you use the maf with a cai? Does it come off the stock airbox?

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

Yes you would still use the MAF iirc there are 3. Allen key head bolts and it will pull right out of the air box!

If your 05 is like my 04 the maf just screws off with a flathead.

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My 05' is like that as well.
I rented an 07' a few years back and it was better.
I suspect it is due to the fact the 05' is a "transition model".

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

I thought 04 was the transition year? I'm glad to hear someone else has experienced this.I'm wondering if a zzp flash would make it on par? Or if I would need a 06+ pcm to gain.

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

A friend of mine was a GM engineer and explained it to me [it made perfect sense].
The styling was a transission in 04'.
The upper intake was changed from plastic to aluminum in 05' as well as going to fly by wire throttle control.
05' was the first year the GP achieved SULEV emissions staus,IIRC [super ultra low emissions vehicle,IIRC].
I rented an 07' three years ago last August for trip to Columbus Ohio and it was a holy terror for a N/A V6.
That sold me and I bought my 05' about a 16 months later.
The car just never seemed to "snap" the same way as the rental did.
My dad's 07 seems to have more snap as well.
Hmmm?

05' was the first year for the aluminum UIM and necessitated a different Cal' for the timing and fuel tables due to the absorption/retetention of more heat creating a hotter intake charge.
I *believe* they erred on the side of caution when they did the 05's - for warranty/emissions reasons.
They *may* have improved things with better Cal's/cam specs in the 06' and up versions.
I do notice that if I disable traction control,the car has a *tad* more snap during throttle roll on.
I do know that some of the engineers in the engine dyno lab have played with predictive throttle Cal's - basically trying to figure what you want by your rate of throttle input.
Could be they went "too far" with the first aluminum UIM cars?
I wonder if there's a dealer reflash for people with this complaint?
Maybe when I see Will at Overkill,I'll ask him if there is a difference?
I think I'll be needing a reflash anyway.

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

Thanks for the info. I would love to hear what Will has to say. If the engines are physically the same I would think we would be able to flash it somehow?

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

I believe the 05' computers are the last year for electrically erasable computers.
Anything after that,I'd have to open one up to see what they did.
Maybe they're UV erasable after 05'?
They used to do that on the Grand Nationals Proms....of course you could swap chips on those as well.

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

^^^^^Original message updated with my new findings! ^^^^^^

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

I'm not surprised.
The 07' I rented was a single exhaust.
Relatively speaking,more exhaust back pressure is usually better for lower to mid range RPM's.
If you lower B/P,the cylinder scavenging effect at low RPM's becomes less [due to less exhaust velocity].
The higher the RPM,the better the scavenging effect with the above parameters.
To bring the bottom end torque back up,you need to rejig the curves [more timing,etc,].
We're talking Helmholtz theory here,so optimizing outside the "passband" on an emissions engine becomes tricky.
Hope that helps.

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

Ok, so then i have 2 questions....

1) does this mean factory gt's (pre 06) are actually slower then base models with single exhaust? or are the computers tuned differently in the gt's to get them back up to single exhaust specs?

2) My mechanic recommended unplugging the battery for an hour to try to let the computer relearn or whatever. Sounds kind of crazy but i have seen it work with other cars.

Looks like i am going to try to put a cai on them and see if that brings them back to life

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2005 Grand Prix: SPO Spoiler, SE Front Extenion, Painted rear extension white, SPO Grills, Body Color painted Tails, 6000k HIDS
2006 Grand Prix: SPO Grills, Painted Body Color Tails, 10000k HIDs

1. I don't know about the cal's on the two types.
I'l have to ask Sherm' and see if he knows.

2. That should get you back to a factory baseline.
I don't think you need an hour,but go for it...it can't hurt.
I have a modified air box,rotated dogbones,ported/coated PEMs and the upgraded alternator output wire to the underhood fuse box.
My car really likes the 91 octane fuel [Sherm' told me it would...hmmm].

If I turn off traction control,the car will jump out of the hole.
From what I remember,the single exhaust 07' I rented [45 miles when I got it] seemed to have more bottom end torque than this one.

For a cold air kit,have a look at this thread:

04-08-grand-prix-discussion-f19/post-your-intake-setup-pics-t17941.html

Interesting ideas there,depending on which way you want to go [stock box vs. aftermarket style].

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

PCM: If you're missing back pressure, grab a GT pcm or depending on your car and aftermarket GT PCM and see what that does for you. It should even out the powerband and take car of the lack of back pressure.

The Cold air should help, but probably won't do as much for you as a PCM would... and New vs New the aftermarket PCM would be a more cost effective approach.

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First things first the 2004 GPs had the Aluminum upper and drive by wire.

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04 GTT - Retired
Best ET 13.016
Best Trap 115.56 MPH

I got the transission year wrong?
Sherm' will kill me!

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

yuppers, as for the exhaust dual\single I can't see it making that big of a difference, when you swap are you swapping from the downpipe, or are you swapping from after the Catalytic? If from the downpipe, then perhaps a cat is clogged.

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2006 Grand Prix GT

i can gurantee that the catback exhaust is doing nothing to hurt your performance. id givi it a tune up.
the fuel filter can hold these cars back pretty bad. how many mile does the car have?

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2000gtp vs cam,105s,ssic,42.5s,n*,lq4,pacesetters,portedgen3,and someother stuff-demod
1999gtp f1 hood,slp gen1 spoiler,ssac headers,tune,3.4 of doom. holding back for turbo build.

I'd love to do that,but the fuel filters on the 05's and up are part of the fuel pump unit,IIRC.
I did just have a ZZP 2.5" D/P and Magnaflow Cat combo installed at ZZP's shop last Thursday.
The car was throwing a code by Saturday afternoon.
I asked Jerry about that before the install and he said no problem....it shouldn't throw a code.
I guess it's time for a proper Cat.
Sherm' and I liked the increased throttle response though.

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!