As your car is getting to 120 mph I'm assuming it is getting there relatively enthusiasticaly.
Once you get above that sort of speed you are in the realms of high drag and thus require big power to push the car on. You could well find that your car may go faster but it will need a bit of patience.
Whilst Porsche tend to publish conservative figures, they put the top speed of a Lux at 135 mph so you are not a long way short. I don't remember seeing 120 mph down Revett Straight at Snetterton in my Lux so perhaps you are doing well. Even BKE goes like stink to 120 and then seems to start thinking about it and he's reputed to have 300+ bhp [
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Porsche graph figures on acceleration indicate:-
2.5 Lux
0-60 IRO 7 seconds
0-100 IRO 23 seconds .'. 16 seconds for that extra 40 mph
0-120 IRO 39 seconds .'. 16 seconds for a further 20 mph
Try looking at the second hand on your watch and imagine the speed increasing. 16 seconds seems like forever, for 20 mph.
By comparison a 220 turbo will hit 100 in 15 secs, 120 IRO 24 seconds, but again tails off requiring a further 17+ seconds to squeeze another 20 mph out.
Based on power and drag, again Porsche figures, the 924S top speed is 2mph higher and 0-62.5 is .2 secs quicker. The 924 is 20kgs lighter but it gains on top speed because it has a lesser frontal area, thus less drag.
I'm afraid you could spend shed loads on your Lux and end up going almost imperceptably faster. At the end of the day, if you want all out power, you will have to do what I did and sell the Lux and get a Turbo. On the other hand, within licence retaining speeds, the agillity, poise, and linear delivery of the Lux makes it every bit as enjoyable as a Turbot.
