If the question refers to some price-is-no-object drag strip dedicated race car comparison, I would say that the car with the gigantic turbo plumbing sitting where the passenger seat USED to be will probably dyno more ponies than a KB...
But then a top fuel dragster will blow them both away.
The two different approaches to adding power have unique advantages and drawbacks to both approaches.
In general, the twin-screw blower is something a person can live with day to day in their daily driver (again, if installed properly with that in mind), whereas turbos in these cars that produce comparable power are considered less suited to daily driver status. Small turbochargers (or, as the larger trucks are now running, sequential turbocharger arrays) are better suited to this role, since they will spool up quicker and reduce akward lag time and driveline shock, something the twin screws do not experience of course.
Setting the baseline of the query as being installed on a stock 4.6 IMPLIES that the upper power output would be limited by whichever stock component fails first, which would probably be the rods, though the clutch or transmission would be preparing to give up the ghost at about the same time.
So the correct answer would be "neither", since the conditions of the test would insure that other components in the drivetrain would fail before either combo could be fully taxed to the limits of their power potential.
This is an article I wrote a while back on this subject for AFM:
New Supercharger Tech for the Ford Mustang: Part 1 of a Series
2008 and 2009 promise to be important years for Mustangs, and superchargers will figure prominently in the picture.
Eaton has been long known for its positive displacement, Roots-type superchargers (such as those featured on the 2003-2004 SVT Cobras), so its no surprise they are near the front lines with their Eaton Twin Vortices Series (also known as the Eaton TVS). It’s a patented design that features twin four-lobe rotors working at a 160 degree twist. This unit is very different from the original Eaton superchargers, which have three lobes at a milder 60 degree twist.
The extra lobe and added angle of attack, along with a thoroughly upgraded air inlet and outlet ports makes for better flow – and better flow into the engine equals more power.
The new blower works cooler – quieter – and has less vibration, all big advantages over the earlier Eaton designs. Companies using the new TVS in their cars or kits can now use a smaller unit to produce the same power as an older-model unit. This has obvious advantages in terms of finding space for the installation due to the often crowded conditions under the hood. Aerodynamic and cooling considerations become simpler, given the ability to use smaller superchargers that create less heat while also accomodating a trim, low, hood line.
Eaton’s new TVS superchargers are already making a splash in the performance marketplace. In Australia they were featured on the TRD Aurion, then Roush featured them at the 2007 SEMA show on one of their fast Mustangs. The biggest news is that General Motors is planning to install the Eaton TVS supercharger on the 2009 Corvette ZR1 and 2009 Cadillac CTS-V.
For those wondering what superchargers are all about, there are a number of different types of superchargers. The most commonly used models in automobiles are Centrifugal (aftermarket) and Positive Displacement Superchargers (OE and aftermarket).
Centrifugal blowers work in a manner similar to turbochargers, utilizing a small turbine spinning at high rpm’s to pull in air and create boost. Whereas turbochargers are powered by the channeled flow of hot exhaust gases from the engine, centrifugal superchargers are belt driven, and therefore exact a certain parasitic power drain from the motor. In modern superchargers, this inherent cost is minimized by advanced design, and more than compensated for by the added power generated by the boost. (Examples of companies that make centrifugal superchargers: ProCharger, VorTech, Paxton, etc).
Positive displacement blowers are different from the centrifugals in that they create added boost via a positive gain in air displacement using large, lobed screws which turn in a confined, pressurized case. They are less flexible as to their location compared to their centrifugal cousins, for they work best when they incorporate the intake manifold, where the centrifugals can be mounted anywhere they fit in line with the serpentine belt and crankshaft. Packaging on most OE installations favor the positive displacement sc’s, so they dominate the original manufacturer market. Like the centrifugal superchargers, they are also belt driven, and exact the same sort of parasitic power loss. (Examples of companies that make positive displacement superchargers: KenneBell, MagnaCharger, Whipple, etc.)
The TVS from Eaton (all components Made in America) operates with a high thermal efficiency (up to 76%). Since the efficiency of any supercharger depends largely upon how much heat it produces as it provides boost, this high efficiency pays dividends in terms of performance, drivability and efficiency.
When Ford failed to follow up the success of the 2003-04 SVT Mustang Cobras, some doubters felt that the day of the supercharged Mustang had passed.
The arrival of powerful supercharged ponies from Shelby, Saleen, Steeda, and Roush would indicate that word of the supercharged Mustang’s demise was very premature!