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PostPosted: Mon May 12, 2014 2:59 pm 
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Location: Santa Fe, NM.
Year and Trim: 2005 Pontiac Bonneville GXP
Hey what's up guys! Got a few questions for ya'll!

Since the N* can't be modded, I want to know if there is any suspension mods you can do to a Bonne GXP.

I want to put the power that already has, good to the ground. I mean, I've done some runs and I get wheelspin off the line and the weight shifts to the back pretty bad, more than my GTP.

I want a stiffer suspension and I want to lower the car, so is there any coilovers for the GXP?

And last, what is the widest tires you can fit in a GXP without modding anything? (i want to get some drags)

Thanks guys!

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PostPosted: Mon May 12, 2014 3:01 pm 
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Location: CHICAGO
Year and Trim: 2006 STS-V, 2004 GTO, 2009 G8 GT
Wrong section.

However to answer your question, the car is already lowered from the factory so it sort of limits what more can be done.

I'm sure simple stuff like bushings, and wider tires will help, but anything more (such as continued drop and other things), and you're going to upset your ride and comfort quality. You could upgrade brakes (Brembo's as Seth did), but it would require custom fabrication to develop a conversion bracket to mount the calipers.

Again, on the point as we discussed about the engine. If you bought this to modify, you bought the wrong car.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2015 Chrysler Town & Country Limited Platinum: Mommy's NEW RGC
2007 Chrysler Town & Country Limited: Daddy's beater affectionately called the Rolling Garbage Can or "RGC" for short
2009 Pontiac G8 GT: L76, Sport Red Metallic
2009 Chevrolet Impala SS: LS4 V8, Victory Red
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PostPosted: Mon May 12, 2014 3:36 pm 
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Location: Santa Fe, NM.
Year and Trim: 2005 Pontiac Bonneville GXP
Haa... I thought I put it in the Suspension section my bad!

Well, ride and comfort quality is not an issue so it's fine if its all stiff, all I want is to try to get rid of the weight shifting thing as much as possibe.

Brembo's? I could use some of that!! Or, are there any other brakes I could use without modifying that much?
Polyurethane Bushings over the rubber ones?

And do you know how wide a tire is able to fit in the front without modding?

I've been told many times that my GXP can't get any faster but I want to try to fight and beat the odds :)

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PostPosted: Mon May 12, 2014 4:22 pm 
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I will say this. I'm not the suspension expert when it comes to aftermarket support. I was the repair guy when something went wrong... Fix it please...

With that said, there is NOT a lot out there for this platform. When the SSEi guys raid the GXP parts bin for suspension goodies (as many do), what does that tell you. You pretty much have it from the get-go. Yes, there are little things you can do. Poly bushings (if you can find them), better struts/springs combo, and bigger/wider wheel/tire combos. The brake thing, Seth (Sethjamesromrodt), created a bracket to mount a set of Brembo 4 piston caliper to the car. But that was his one-off setup.

To answer your other question as to the widest tire combo... Don't know. Never ventured to check it out, because for a FWD car, with a fairly wide set of tires as is, there isn't a lot more room up front to stuff bigger meats, at least if you plan on being able to have full lock to lock capability.

Again, I'm sure some of the more adept suspension gurus can chime in. But overall, you're not going to convert this from a 4-door family sedan to a canyon carver.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2015 Chrysler Town & Country Limited Platinum: Mommy's NEW RGC
2007 Chrysler Town & Country Limited: Daddy's beater affectionately called the Rolling Garbage Can or "RGC" for short
2009 Pontiac G8 GT: L76, Sport Red Metallic
2009 Chevrolet Impala SS: LS4 V8, Victory Red
2003 Chevrolet Suburban 2500: Doeskin Tan - new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Mon May 12, 2014 4:29 pm 
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You already have the best OEM brakes and suspension that any Bonneville came with. No one makes coilovers, the only thing that's available are custom lowering springs from Coil Spring Specialties (IIRC), which is who several members on here have had make springs for them.

The squat you get is from poor weight balance and suspension design more than bad springs. You could literally put blocks in and it will still want to do it...

There are polyurethane bushings for the swaybars and endlinks at least, not sure about any others.

IIRC the widest tire you can run without hitting the strut with stock wheels/tires is 255? Also, anything wider than that and you're going to go way under the recommended width for a tire, since the GXP wheels are 8" wide.

The brakes that Seth used were Cadillac CTS-V calipers with BMW 7 series rotors, not sure on the brackets he used. And he needed longer studs and wheel spacers to clear the calipers.

It's not that you can't make a Bonneville GXP faster, it's that it's all custom work, and unless you're a fabricator, custom work = $$$. Not like an F-body, 5th Gen Camaro, even a G8, where there is a huge aftermarket behind them. There is virtually none for you...

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PostPosted: Mon May 12, 2014 4:39 pm 
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That combo is common even on the GTO's (with the beemer 7 series rotor due to the taller rotor hat). The Brembo caliper is a 2-piece aluminum caliper used by GM throughout the product line (the CTS-V caliper is the same as on my STS-V or XLR-V's, G8's, SS's, etc, etc...), heck even the same as Mopar uses on their junk. :p It wasn't until the later C6's and the new CTS-V that they used Brembo's Monoblock 6-pot setup.

Anyway, In order to mount the caliper to the front spindle, requires a custom made bracket that Seth fabbed for his. Damian (itsme4g63 on CHC), does the same type of things for us GTO's to convert to Brembo's.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2015 Chrysler Town & Country Limited Platinum: Mommy's NEW RGC
2007 Chrysler Town & Country Limited: Daddy's beater affectionately called the Rolling Garbage Can or "RGC" for short
2009 Pontiac G8 GT: L76, Sport Red Metallic
2009 Chevrolet Impala SS: LS4 V8, Victory Red
2003 Chevrolet Suburban 2500: Doeskin Tan - new plow truck
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Mon May 12, 2014 4:41 pm 
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255's are the widest without interference. MT drag radials work best for the street or slicks for the track will gain you half a second.
Try the airing up the rear shocks to the max, to help transfer more weight to the front.

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