Here's an interesting tidbit about the 2.5's that I found while reading "Porsche 911, R-RS-RSR" by John Starkey.
" ... To take complete advantage of the 2.5 litre class limit, Porsche supplied several sets of components for customers who wanted engiens of this size. In fact, Porsche built two prototype 2.5 liter engines of differing stroke/bore combinations due to a problem they encountered with the first design.
The first design took advantage of the "E" production variant (AKA: 2.4 liter motors) having piston stroke increased to 70.4 mm (previously 66 mm) in conjunction with a bore increased to 86.7 mm: the result was a cubic capacity (2494 cc) at the class limit. Otherwise the 2.5's specifications were as the 2.4 liter unit. In its new size, the engine developed 275 bhap at 7900 rpm and 196 lbs/ft of torque at 6200 RPM.
The problem with the first 2.5 liter engine was that it tended to loosen its flywheel bolts, or in extreme cases break its crankshaft. There was little doubt at the factory that this was due to the longer stroke now being used and so some engines were built using the previous stroke of 66 mm whilst employing "Nikasil" cylinders with a bore of 89 mm. This resulted in the same power and torque figures as the long-stroke engine without its fagility"
I'm suspect that Roland may have even more behind-the-scene history on this. It's an interesting proof that (all other things being equal and reasonably optomised) that changing the bore-stroke ratio doesn't change the HP or torque figures. Both are a function of the amount of air pumped, which is 1.25 liters per rev. Anyhow, I'm sure that Porsche figured the problem out.
PS: Speedvision was rebroadcasting the Goodwood Speed event (Hill-climb) yesterday and they showed one of these 911ST's running the hill. The car seemed to be an absolute Rocket (and rev'd like it too!), but then the driver stuffed it. He said afterwards that "The car just started turning faster then I could"
