The 928 Porsches are great cars. Build like a rock, great brakes, great high speed (100+) stability, and quite comfortable, if a bit cramped.
The 2 valve US versions (rated at 219-234 hp) are the 78-84s. The 5 sp usually runs low to mid 15s at 89-91 mph. The autos, mid 15s to low 16s at 87-90. Top speed 135-144.
The 85-86 US version had the US only 5 liter 32 valve 4 cam engine. It was rated at 288 hp/302 tq. Porsche went to the bigger 5 liter 32V engine for the US to boost power and still meet US emissions laws. The europeans still had the 4.7 liter single cam engine. The 5sp US 85-86s will usually do mid 14s at 96+, the 4sp autos, high 14s at 94-96. Top speed 148-152.
In 87 all 928s , US and Euro, had the 4 cam engine rated at about 316. 5sp cars do 14.2-14.6 at 97-101, autos 14.4-14.7 at 96-99.
Top speed 160-165.
In the early 90s, the engine was punched out to 5.4 liter, rated about 340 hp. The 5 speeds were doing 13.8-14.1 at 101-103. Top speed was 168-174.
I have a 86 928S auto. I got it back in Nov 94 with 22K miles on it. It now has almost 100K, and still feels as good as ever. I would wager that it could still pull a 14.8 at 95, and it still goes an easy 140 without effort.
The basic engine is usually good for 200+K miles, the auto tranny has Mercedes-Benz guts, the car is all galvanized steel with some aluminum panels, it's a solid piece. But....
Upkeep is not bad, but even basic repairs are big bucks if done right. The electrics can be flakey, some of the minor controls are less robust than in a Regal, the AC 90 degree+ heat is sad, and the leather squeaks in cold weather.
Overall, it's a great overall car.
If you want some more info, e-mail me.
ny6814s@aol.com