Bonneville and GP GXPs

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Thread: Bonneville and GP GXPs

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    R2-D2 Astromech Droid Premium Member Neanderthal's Avatar
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    Bonneville and GP GXPs

    I ran across an old Car and Driver (Sep. 2004) Bonneville GXP test, and found the numbers compared to the GP (C&D, Oct. 2005) interesting:

    GP Bonnie
    curb wt. 3630 3940
    final drive 2.93 3.70
    top gear: .70 .68
    engine: 325 c.i. ohv 279 c.i. dohc
    HP [email protected] [email protected]

    TQ [email protected] [email protected]

    0-60/100: 5.7/14.8 6.9/19.0
    1/4: 14.3 @98 15.4 @ 91
    70-0: 174' 187'
    G: .82 .79

    When I started looking into these cars quite some time back, the bad news I kept hearing about the Bonnie's Northstar definitely turned me off that package. A Bonnieville SC 3.8 would have been a good package.

    Why GM didn't use the 325 c.i. in the Bonneville GXP is a mystery to me, it's just IMO a shame they went with lower power and more "sophistication" vs. a better mill.

    The 5.3 puts out up to 320 HP and 340 TQ in various truck applications. Granted, the GP mill is a somewhat modified 5.3, but those are good numbers for a Bonneville GXP.

    And so go...The Days of Our Lives. Or Water Under the Bridge.
    Last edited by Neanderthal; 01-01-2010 at 05:48 PM.
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    Firebird Concept (the turbine one) F14CRAZY's Avatar
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    Re: Bonneville and GP GXPs

    Funny how the Bonneville has the good trans but bad motor, then the Grand Prix has the bad trans but good motor
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    Re: Bonneville and GP GXPs

    Quote Originally Posted by Neanderthal View Post
    Why GM didn't use the 325 c.i. in the Bonneville GXP is a mystery to me, it's just IMO a shame they went with lower power and more "sophistication" vs. a better mill.
    One word: Torque Steer

    Well okay, it's two words.
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    Re: Bonneville and GP GXPs

    Quote Originally Posted by F14CRAZY View Post
    Funny how the Bonneville has the good trans but bad motor, then the Grand Prix has the bad trans but good motor
    The Bonneville GXP concept started as a promotional show car for GM. Full-sized attitude was the goal, and Pontiac responded by smoothing the Bonneville's lines and tuning up the front and rear fascias. Dark Argentinean Blue was the chosen color, accented by smoked headlights and taillights, Xenon fog lamps, and tinted glass.
    The body was dropped an inch and a half for a more aggressive look, and 5-spoke, 19-inch rims showcased mondo rubber and upgraded brakes. Although GM engineers wanted to drop a V8 into it immediately, the idea of installing a big mill into a turntable-bound Pontiac couldn't be justified.
    Instead, the Bonne's blown 3.8 was treated to a K&N filter, more boost, and a Corsa exhaust system, which pushed horsepower from the stock 240 ponies to 270. Not surprisingly, when Gary Cowger and Bob Lutz eyed the GXP they immediately fell in love with it.

    It was sent to the 2002 Chicago Auto Show, where it was applauded as a bold step forward for a division lacking the excitement that it advertised.
    After the superlative-filled Chicago venue GM knew it had something strong on its hands, and changes were made to prepare the Poncho for SEMA.
    But it stood to reason that distancing the upscale Bonne from the Grand Prix by offering a smoother V8 might make it stronger yet.

    And here's where this saga gets interesting: sometime between February and October, the GXP's supercharged 3.8/4T65E drivetrain lost out to a 4.4-liter, naturally-aspirated V8 connected to a stronger 4T80E transmission.

    Most of the new motor's specifications are still hush-hush, but it has been said that the 32-valve, quad-cam mill (for the most part a carry-over from the Cadillac-based Olds Aurora V8) will more than likely share the Cadillac 4.6-liter Northstar's architecture and all-aluminum construction. In fact, the GXP's motor could very well be a de-stroked version of the L37 Northstar producing 285 horsepower.
    How much torque it will make is anybody's guess--we're willing to bet that GM won't have to push the 305 lb.-ft. torque capacity of the 4T80E transmission, but needs more than the 280 lb.-ft.-rated 4T65E can give.


    the 19-inch wheels on the concept will be replaced with more reasonably sized 18-inch units wearing rubber with a W speed rating. GXP's big rollers and V8 power will require structural modifications, although no specific changes to the chassis, save for bracing, have been released.

    However, the GXP will share the Caddy's stronger tranny. Unfortunately, this strength comes with a price: the 4T80E is nearly a hundred pounds heavier, at 292 pounds versus 195 for the 4T65E. It has been estimated that a 24 percent driveline loss exists with this trans, which is higher than the 4T65E's estimated 21 percent. The 80 does have slightly higher gear ratios down low--2.96 and 1.62 for First and Second, as compared to 2.92 and 1.56 for the 65. But when factoring in the driveline loss and extra weight, we suspect that the 285-horse, naturally aspirated GXP won't be any faster than the original concept's 270-horse 3.8. ...we're looking at mid-14s in the 95 mph range on a good day. Not lightning-quick, but it will still beat the SSEi's mid-15s like a stray dog.


    http://www.gmhightechperformance.com...ure/index.html


    If you scroll down to the "GXP" tag, you'll see an unfortunate bit of (ill) fortune-telling.

    Quote Originally Posted by Tomko View Post
    One word: Torque Steer

    Well okay, it's two words.
    I'd guess the V8 Bonnie has TS. As does the 3.8 SC. In fact, my 3.8 Regal had a wee bit o' it.

    It's just something to acknowledge, adapt to, and enjoy.
    Last edited by Neanderthal; 01-02-2010 at 01:05 PM.
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    Re: Bonneville and GP GXPs

    The LS4 wasn't availbable when the first Bonneville GXP came out so they put the Northstar in there. Once the LS4 became available the Bonneville's days were numbered so there was no reason to spend the money to certify it for so few cars.

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    Re: Bonneville and GP GXPs

    Also consider that the Bonneville's platform mates already used the Northstar
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    Re: Bonneville and GP GXPs

    Having driven my grandfather's '06 Impala SS many a time and owning a '00 Seville STS, I can say for sure that the Impala has way too much torque steer for it's own good. At times, it feels like the car is going to lose control. On the other hand, my Seville rarely ever suffers from this problem. The only time I ever really get it is when giving it gas out of a corner, and even then it's minor. On the other hand, the Impala is a much better handling car thanks to a good 300lb weight difference.

    Bonnie GXP's are nice looking cars, but I do think the car would have been better off with a S/C 3.8. The motor is a little more coarse, but much more reliable. Northstar's are a hit or miss when it comes to reliability, and even then you have to deal with the oil consumption and other thing besides the headgaskets that can go wrong.

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    Re: Bonneville and GP GXPs

    I think the Bonneville GXP is one of the best looking cars on the road at the time and I still do.

    It's unfortunate the 295-300HP Northstar was not put in it. Too bad it was too early for a 6 speed automatic.

    I have Car and Driver comparo with the Corwn Vic, GXP and Hemi 300C. You can guess the results.
    Love to get a used one..if they are cheap(er) to own.

    Hate the Grand Prix---interior is bad, among other things, IMO. (not that the Bonneville was super)
    Last edited by avro206; 01-02-2010 at 06:18 PM.

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    Re: Bonneville and GP GXPs

    Quote Originally Posted by avro206 View Post
    It's unfortunate the 295-300HP Northstar was not put in it. Too bad it was too early for a 6 speed automatic.
    I would have liked to see it with Orenda Iroquois power. But since you're RL-206 you really are the one that got away...
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    Re: Bonneville and GP GXPs

    Quote Originally Posted by Tomko View Post
    I would have liked to see it with Orenda Iroquois power. But since you're RL-206 you really are the one that got away...
    lol someone knows their stuff!

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    Re: Bonneville and GP GXPs

    The 2003 on up Northstars seem much better than the 2002 and older versions which suffered head gasket leaks, oil consumption and other issues like piston pin noise and coolant leaks. I have driven and interviewed folks with 2003 and 04 GXP's that haven't had any issues, 2006 on up Lucerne owners and numerous Deville and DTS cars from 2005 to present. There is the occasional issue but it seems like a better engine these days but still hard to work on of course. The GXP Bonneville used the 275 HP version of the Northstar but paired it with the 3.71:1 gears as apposed to base Deville/DTS and Lucerne CXL/CXS models from 2006-2008 which all used 3.11 gears for better highway mileage so GXP will be quicker than the other 275 HP Northstar equipped cars. I'm curious how the 2009 Lucerne Super is with the 292 HP 3.71 geared HO Northstar as it's a bit lighter than the DTS.

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    Re: Bonneville and GP GXPs

    Quote Originally Posted by F14CRAZY View Post
    Also consider that the Bonneville's platform mates already used the Northstar
    I'm sure that this has more to do with it than anything else.

    I always liked the looks of the BGXP. GPGXP is alright, but I'd go with a LaCrosse Super for the sleeper
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    Re: Bonneville and GP GXPs

    What is the Largest Size engine,
    that fits a 6 speed FWD Trans?
    (6T70/6T75)

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    Re: Bonneville and GP GXPs

    These GXP Bonnevilles and GP's are going for dirt cheap on ebay. 8 grand will get you one with under 50k miles.
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    Re: Bonneville and GP GXPs

    I quite prefer the Lucerne Super to the Boneville GXP, which was a car that actually performed worse in many ways compared to the DTS and did not handle much if any better in the real world. Also something to keep in mind , the 4T80E is at best a band aid that needs heavy torque management and huge powertrain losses to contain even the stock 300 hp. I had my 4T80E electronically modified to change shift points and for firmer shifts, so it held up but transmission problems are fairly common in Northstar cars. I will never forget when I put my STS on a dynamometer and the sum total of all of that Northstar sound and fury was 212 hp to the front wheels stock.

    The STS also is a far better chassis, that especially with the right tires would literally leave a Bonneville or GP GXP in its wake on a twisty back road.
    I want a car so violent that the mere thought of full throttle would cause a heart attack. That actually going wide open throttle in would result in nothing less than instant death!
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