there is a reason why the GXP is FWD... read this article below
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There are some packaging and efficiency advantages with transverse mounting of the engine in a FWD application. Since the power flow does not have to "turn any corners" there is no high friction right angle gear drive. The hypoid style gears used for right angle drive (typically seen in the rear axle but the longitudinal engine FWD Eldorados had a hypiod gearset also in the final drive) are a high friction device and cost fuel economy and generate heat.

In the transverse arrangement the crankshaft is parallel to the shafts in the transmission (more properly called a trans-axle in this situation) so chains can be used to transfer power from the crank to the trans. The drive axles run off the same centerline as the main shaft in the transmission so that there are no friction adding gearsets or right angle drives. All this makes a more efficient powertrain package due to the friction reduction.

Since all the powertrain in the transverse FWD cars is mounted on the engine cradle it makes it much less complex to build the car as there are no long driveshafts to the rear of the car and no rear axle delivering power to the rear wheels. The car also does not need the heavy structure in the rear to contain the power delivery from the rear wheels as the cradle/subframe that holds the engine and transaxle also contains all torque reaction of the powertrain and tranfers the motive force from the wheels to the car to make it move.

Transverse powertrain packages can be designed and manufactured very compactly with the trans tucked beside the engine. It also allows for good powertrain structure by attaching the transaxle directly to the engine block where it mounts besides it.

The Northstar engine was designed for transverse mounting from the very beginning. It was highly optimized to package in as small a fashion as possible for the transverse mounting. That is why the water crossover casting is on the rear of the engine mouting the coolant passages into and out of the heads and block and why the water pump is at the rear of the engine. It is much more efficient to package it at the rear of the engine in a transverse setup where there is room over and around the transaxle bellhousing that is unused otherwise. With a clean sheet of paper engine like the Northstar the cooling system flow and ports could be designed like this from the beginning since the engine was not a longitudinal engine converted to transverse.

The most telling factor that shows the transverse optimized design of the Northstar is the fact that the right bank of cylinders is staggered ahead of the left bank. Most longitundinal V8 engines had the left bank of cylinders staggered forward. Since the right bank was up against the firewall anyway and there was no room for accessories on the right side the right bank was staggered forward on the Northstar so as to leave as much room on the left (front) side of the engine where the accessories would be. This is why the Northstar has number 1 cylinder on the right side and not the left.

Understand that there is no "perfect" powertrain mounting or architecture. There is a case for longitundinal mounting as well as transverse just like there is a case for front wheel drive and rear wheel drive. It all depends on the application and mission for the vehicle. For a passenger car the transverse FWD architecture is very effective as it takes the least amount of room and it is very efficient without the right angle drive in the system.

Also, the safety of having everything protecting you up front.

The one drawback is having the transmission so close to the engine, it gets a lot more heat than the one mounted behind the engine.

The GXP is front wheel drive because the Bonneville was only 4 years old in it'* current configuration when it was released. The cost to redo the entire platform for rear wheel drive would have been very high, and not enough to come close to making money off of the 4000 or so units that were produced in 04 and 05 model years, GM doesn't have an all wheel drive setup that would work on this platform either.

It most certainly was not kept as front wheel drive for performance reasons. Show me one sports car (not a sporty model of a sedan) or higher that has rear wheel drive.

Personally It was a refreshening of the Bonnie to try to boost sales/image, however the model we have now should've been released instead of the SSEi in 2000 in my opinion. It'* too little and too late to compete with new cars in the segment.

naw, I meant that the GXP was FWD because it uses the N* engine. There is no Northstar engine that is RWD. They were designed with only FWD in mind. To use RWD in the GXP the entire engine would have to be reworked.

The Northstar was redesignd in like 02 or 03 for the SRX, and now it'* in the XLR, the STS as well... ALL are RWD or AWD based off of RWD setups.

or they could have used the LS1 or LS2

I agree that the XLR and the STS use the N* in a RWD drive configuration but when Cadillac wnated to give their sedans a real RWD power house they chose not to use the N*... whether or not it is because of inital design and set up for a FWD car I don't know.

I like my FWD N* Bonnie. I bought it for the comfort and size and am not worried about it being a road dominating muscle car. It has plenty of power and handles slendidly on the highways in central Florida.

If I was ready and willing to pay for a true performance sedan it would probably be in one of the German brands and to be honest a 500hp E55 AMG while extremely luxiourious and powerful would not be a cost efficient alternative for the syle of commuting I have to tolerate.