this was copied directly from bimmerforums.com
this is a what STS says as for benefits of the rear mount and a members own theories to contrast or concur with STS
(again this was taken from another forum so the arguements are from the guy who had originally posted this (i know none of his credentials))
Lower underhood temperatures. No need to worry about melting wires, hoses, or other engine components, as with a front-mounted turbo.
A properly designed kit or custom build will account for heat management, and remember there are wires and components underneath the car.
Ease of installation. STS turbo systems can be installed in about 8 hours with standard tools and average mechanical ability.
A well designed and documented front mount kit could most likely be installed in a similar time but I dont have hard numbers to support this claim as I've never installed a kit.
Cooler oil to the turbo. Cool oil is better for both the turbo and engine.
They are inferring that because the turbo doesn't absorb as much heat as a front mount due to the loss of thermal energy along the exhaust tract (yes energy) that the oil doesn't have to perform as much of its secondary function of cooling the turbo bearings as it would in a front mount setup where the majority of that thermal energy is mostly maintained except for a small amount that is absorbed into the turbo (housing, shaft, turbine, and bearings).
Well first off a lot of turbos are water cooled which reduces the amount of cooling the oil has to perform to nill, secondly any heat gains to the oil can be offset with a properly sized cooling package, again heat management is key. Last having to route oil lines all the way to the rear of the vehicle is a liability I wouldnt want.
Performance Sound. The turbo acts as a muffler and sounds like an aftermarket performance muffler. Turbo spool and rushing air from the blow-off valve make a unique sound that will turn heads!
Um in a front mount setup the turbo also acts like a muffler and if you want the cool sounds it can also be had, this is a pretty crappy reason!
No need for major modifications to your vehicle. STS systems are designed to "bolt-on" to factory mounts.
Again easily achievable with a front mount kit.
Increased gas mileage. Unlike a belt driven supercharger, the turbo utilizes "wasted" energy leaving your tailpipe. Most of our customers get 1-3 mpg increase in gas mileage compared to their original stock mpg numbers.
Saying that a performance modification that makes more power will consume less fuel than its OEM setup is ludicrous. More power equals more air and fuel!
Converts back to stock in about an hour.
Well this is a plus if its true but I find it hard to believe, but Im sure it does take only a small amount of time compared to a front mount kit.
More room under the hood. Future repair work or modifications will not require the expense of removing the turbo system to allow access to engine components.
This is another benefit to the remote setup.
Lowest Intake Air Temps. Low IAT's equate to more horsepower per pound of boost than any other forced induction option. STS intake piping provides built-in intercooling. Add the optional intercooler, and IAT's drop even further.
Intake temps will not be any better than a properly designed front mount kit or build with a proper intake setup. In fact I would say that a front mount setup would be cooler and more efficient due to the intake point being in a more optimum position thermal and pressure wise.
The idea that the intake piping offers a degree of heat expulsion and acts like an intercooler is true to a small degree but long intercooler piping can lead to large pressure losses which is much more detrimental to performance than a slight temperature reduction (and im going to say very slight)! Another issue with intercooler piping going the length of the car is speed bumps and other road obstacles, the tubing is more prone to damage. Last but not least you have an increased intake volume that will tend to reduce throttle response!
So they are again making pretty bold claims with the, "Low IAT's equate to more horsepower per pound of boost than any other forced induction option" comment.
Approximately 500F lower turbo temperatures. Eliminates the need for a turbo-timer, which allows the engine to run after the car is shut off in order to cool down the turbo and prevent oil and bearing damage.
Again this isnt nescessarily a good thing you have lost a lot of thermal energy that could of been put to good use!
Denser exhaust gasses drive the turbo turbine wheel more efficiently.
Hum Im going to guess they are saying they are denser due to being cooler but at the same time they have lost alot of velocity that could of been used to spin the turbine!
Turbo is exposed to ambient air rather than underhood air. Allows for better cooling of turbo components.
What components need to be air cooled to function more efficiently?
No need for expensive headers, mufflers, or exhaust systems.
Turbo is closer to the tail pipe outlet. Provides a better pressure differential across the turbine wheel which promotes better flow across turbine.
These are some pretty good points especially the last one about pressure differentials which in theory is true with a turbo wanting minimum restriction after the turbine, I believe a megaphone style outlet is the ideal. But again I would want to see some hard numbers comparing a conventional front mount with a rear mount to believe the advantage goes to the remote mount setup.
Better weight transfer. Increases traction because the bulk of system is mounted in rear of vehicle rather than up front.
Sure, this is a good point it does keep weight off the front of the vehicle.
Less noise and heat in the passenger compartment.
Good point about the wasted energy . . . . . err heat. Less noise is a good thing for some builds I will admit.
Just some food for thought