Just thought I would throw in my .02 on this discussion...
Rereading the Roundel article on the AA S65 supercharged unit, a couple of items caught my attention.
The only performance specs are power numbers at the flywheel, 628 hp @ 8,300 and 450 ft-lb @ 6,000, running 6.5 psi of boost, high flow cats and exhaust. Subtract 20% for powertrain loss and the numbers are 502 hp and 360 ft-lb. Compared to the stock 420 hp @ 8,300 and 295 @ 3,900 ft-lb, approximately a 20-22% gain, including the cats and exhaust.
20% drivetrain loss is excessive in our SMG cars. More like 15-17%. Also, depending on the blower used the torque will come on differently. Roots type blowers have a different power curve than centrifugal. Also, since superchargers build boost as a function of crank speed (RPM), there is a direct correlation between peak boost and peak RPM.
Concerning the G-POWER site, I see no clarification of whether the power increases are gross (at the flywheel) or net (at the tires.) The systems also include modified intake, electronics and exhaust, wonder how much of the increase is from the blower alone.
G-Power only quotes flywheel hp. The blower is the only real gain in HP from G-Power.
No mention of warranty I could find, although I don’t read German.
When I visited their offices and drove in their supercharged M5 they offered a warranty to european customers (spring '08). They may have a USA warranty now that they have resellers in California...not sure yet.
They also state, “Electronics: Custom made software for the standard BMW engine and SMG- transmission electronic control unit (BMW OBD stays completely untouched)”, which means they use a piggy-back controller, which sends BMW’s OBD erroneous information, instead of rewriting the actual BMW code. This is a band-aid approach, the external controller for example, tells the OBD that the engine isn’t getting enough fuel or air, when it actually is, so it will direct the injectors to supply more. On the 335i, in order to raise power, piggy-back units tell the OBDs that the engine is getting less boost than it actually is. IMO, much better to actually rewrite the OBD’s code or replace the OE unit with a complete replacement, as in racing applications.
They do use a piggy back unit, but I believe it operates the other way around. The piggy back unit takes the inputs from the stock BMW DME and then controls the "outputs" (i.e. - fuel output via injectors, etc.). This is a common approach in cars which are not FI cars from factory. It's not uncomon to see AEM or even better units like Motec that are very customizable and expensive. Most stock DME's do not offer the capabilities needed to handled the additional maps for boost and load for example. Those types of capabilities need to be inherent in the DME or you'll need to use a piggy back unit.
Also, you can't replace the BMW DME entirely as it's too "wired" into the other functions of the CAN bus. I looked into it when researching my custom twin turbo setup in Dallas. Not pretty, nor worth the undertaking.
There is one board member who drove a G-Powered M5 in Germany. Afterwords he bought a Dinan Stroker Motor instead.
That was me. I went with the stroker because of 1) Warranty (they did not offer a warranty to North American customers at the time), and 2) price (they were very "proud" of their solution...which I think they have a reality check now based on the ebay pricing I've seen).
Another board member tried a supercharger for his M3 (non-V8) and couldn't get anywhere close to the advertised claims. He switched to a twin turbo unit, which delivered "the goods". Damn fast M3....
That was RaceMX-M3 from this board and he went with an HPF Stage 2.5 which is a single turbo.
I'm fairly confident our blocks can handle a modest 5 pounds of boost, especially since the peak boost level will only be reached momentarily at near peak RPM. Nobody drives constant at peak RPM...you shift the gears a few hundred RPM before redline so you'd only have max boost for a split second.
A turbo application is different and can produce max boost much lower in the RPM band and then hold it at max boost for a long portion of the power band. This is what is so attractive about the turbo application and why it would definitely require lower cylinder compression and forged pistons (and other internals).
Just my thoughts.