Someone on the Ducati mailing list mentioned the 907ie as a good candidate to make some power.
I ported and over-bored (94mm, 944cc) one for Larry Hovind. He road it for almost a full season before he brought it in to have the maps optimized. (I had burned a chip for a 944ie for BCM a couple years earlier, so I had a pretty good starting point.)
Larry rides with a guy who has a K1200 BMW and wanted to 'keep up'.
Below is the final result, with and without an air-box top (runs .014 & .017) compared with Jeff Adkins' 900SS.
The older heads (1990, 1991, 1992) were often 'buggered' in the port department. So, they don't often have superior ports even though they may be ported.
Jeff's heads were pretty good to start with (or should I say, not as bad.) That, and the long inlet may be the reason for more torque. Also, the ignition timing on the injected bike is a little more advanced, than that of the 900SS.
The slightly advanced ignition timing could be ideal if the cylinder pressures are low for the previous reasons.
The 907ie uses 46mm throttle bodies and the previously mentioned shorter inlet length.
Both engines use the same cams and valve sizes. Stock 900SS cams (they first appeared on the 907ie Paso), 44mm inlet, 38mm exhaust.
Suffice it to say, the two engines are a little different.
I don't know how much power will be lost when the paint starts to blister on the air-cooled 900SS.
The 100HP 'thermal' barrier that so many folks refer to has more to do with race-track performance than with street bikes, because you don't build any more heat at a similar cruise speed with a 'built' engine than you do with a stock one (it's the same load). Unless, of course, the fuel-air ratio is wrong or the timing is off.
At sustained WOT the air-cooled engines performance will fall off as the temp rises.