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This next one is a bit more of a curiosity; outwardly it appears as though it is a 'King' spec unit, which was identical to the ProKing but had 6 FETs instead of the more usual 8.

However the PCB is a ProKing unit. I know Francis had a couple like this bitd. I guess the King and ProKing boards were essentially identical apart from the lettering on the reverse so it allowed for a little chop and change. You can clearly see where there are two missing FETs on the reverse side.

Date sticker on this one reads 640 723 (1987 week 23) , so ideal for a CAT SWB or XL build

dinglem wrote: ↑Sat Jun 05, 2021 12:25 pm I guess they would have been considered outdated and large by 1989, although they did still occasionally appear in the magazine tech-spec sheets through '88 and '89 so there were clearly some top drivers still using them. I wonder whether they all had uprated spec units like the Rory Cull version though?

I saw this race report the other day and suspect Rory was the last.
As far as prokings with better FETS. I'm sure there are more out there. But bare in mind a standard proking is rated nominally at 240A (8X 30A BUZ11) or 264A (8x 33A BUZ11 ST electronics)

The Rory Cull team proking is rated at 250A (6x 50A SMP50N05)

Back then it was all about the price of the FETS, like you said size played a part. Nick never made a dedicated Forward only speedo, using the same PCB on forward only version, this obviously had a size penalty.

Christian Sterr of CS electronics had a pretty neat solution for this on his CS rocket 6(1985), The reverse relay portion of the PCB could be cut off during manufacturing allowing for a much smaller FWO version.

Great tech chart - i hadn't come across that one before, so thank you for posting. Being '88, and looking at the date sticker that could well have been the very uprated speedo I now have. I know his parents do not have any more ProKings in their left because i asked them to check!! This was the only one they could locate.

I have another write up from mid-88 also, again featuring Rory and mentioning his Proking... this time it specifically states that it is a forward-only version, which again gets me thinking that this is the same unit I now have.

The giant JR Apex 40meg receiver dates this picture quite nicely also.

Hayden Spreadborough also looks to have a complete Demon arrangement installed as well. Some big UK driver names on that list.

Note the pretty cool 2-speed set up on what looks to be a modified MMS gearbox. Rory's dad still has that 2-speed rear end.... he wouldn't part with it however(!)