Just because the turbo is a "MasterPower" unit and not another maker does not indicate it's a POS. MasterPower makes turbos for many vehicles around the world, and is very similar to Garrett in many ways except price.
Think about this. If you buy a Tarus pistol, it is just as accurate as the Beretta that costs 2x as much... (I know, I own one.)
Same goes for the MasterPower turbo. I have the T-70 version, and it's quality is every bit as nice as the ITS unit I had before, and Garrett units I've looked at as well. Only it was less than a grand...
Reading up on this car, the HP claim is totally within reason based on what this owner has done to the car. The fuel system is capable of much more actually. (850 to 900 should be possible on this car, without the funny gas... and more if sprayed..)
He has the stuff needed to get there.
Standalone.
Fuel
Turbo
Engine mechanicals to handle it.
Why the drama over his straight out exhaust? If you do not like it, build a faster car so you can't see it anymore..
Untill then, I'd be surprised that all you would see is that exhaust getting smaller and smaller in front of you in a race
PS: The only thing I'd reccomend to this owner is getting some real brakes. Even uprated stockers can't hold up to the speed that engine can dish out. Seriously, it's a safety thing at this level of power. The car can go much faster than the stock brakes can effectively slow it down from more than once or twice at most in the same general period of time. (Stock fades away, and becomes worthless, even with good pads, and fresh fluid, there is just not enough mass in the rotor, or enough cooling surface either.)