The rev limit is increased by turning the potentiometer inside it Gaz. Only a small amount of movement will make quite a difference as I found out. Fitted one that had been modified to mine and the car wouldn't run! Gave it 1/4 of a turn and it at least reved around to 6k.

Standard S1 limit is 6500k rpm and series 2 is 6250 rpm.

If you have an S2 fuel ECU in an S1 that hasn't been modified to work with the S1 loom or the loom modded to work with the ECU, then you will have no fueling for on boost or cold start enrichment as the ECU won't be powered up (power and earth pins in different places). S1's had an ECU with a blue sticker and S2's one with a green sticker.