It would be cheaper to buy an S2 if you can find one for sale.
The only engine with more power was, as mentioned, the GTN, which had the 4.6is engine, tuned by Alpina. The S2 had the same engine as the S1
I'm always interested to read comments regarding the 4.4/4.8 V8 because no one is yet been able to get more power out of the engine without major modifications(and this included MMC). As for bolting on a supercharger or turbo, general consensus is that you'd struggle to find space to do it in an Aero and would end up with something sticking out of the bonnet like a hotrod!
It would seem that the variable value timing is the limiting factor and this is what stops you from making and noticeable gains in BHP.
As an aside, what I always found frustrating is the large performance difference
http://www.talkmorgan.com/ubbthreads.php/topics/20075/1between standard engines. Aeroman, Asbo, Boshly, MrTony, myself and a few others all put our cars on the same rolling road, on the same day, and there was, iirc, a 30bhp spread between best and worst performing engines. It would seem that the easiest performance gain would be buying a very strong stock engine, rather than one with asthma!
