Thanks for your interest and owning two Sr8s! hope you enjoy them.
There was a definite order of ‘spec‘ as produced as new , except! 2-5 only ‘special orders‘. I would guess your chassis #87 is one of those special orders.
Early cars were built with Hewland JFR as you see , around 45-50 came the early Quaife Q-tec , which was designed by Quaife as a Porsche replacement gearbox , with facility to turn crown wheel around to give mid-engine drive. This box had an extension housing for our rear 5-6th gear due to width of the planned Porsche gears. Quaife then worked with us on ‘miniQ’ version, where crudely explained we got all 6 gears in same main case without extension housing or subsequent selector shaft extension, by reducing size of parts, we worked together on selection of components and dog rings. This was most prolific box used in sr8 and even the 10- 12 or so final update sr8s last year or so.
So how is your car fitted with Hewland on late chassis number?
Well the clue to me is the Stack equipment along with Hewland.
We changed from the Hewland because of Crownwheel and pinion life.
With hindsight … the 10,000 rpm engine needs an 8 tooth pinion, which was always fitted. The Hewland is rated for the +/- 200ft lbs torque, but only on the 12 tooth pinion as used in F3 etc., the torque capacity reduction between 8-12 tooth is in the order of 40%. To make the pinion live a reasonable service we needed to really optimize the whole package, setting up CWP gears with finesse, to avoid ‘hot spots‘ on the CWP gears, running new components in really well, and finally select suitable proven gear oil. We strongly recommended NEO which seemed to have the magic fix after good running in. All that done, it worked well, the Hewland differential has a performance edge on traction and set up, to keep it on that edge was not easy with the wear we saw.
Performance seekers saw that edge, liked the weight reduction (in the order of 20 kg less for Hewland)
Regarding the stack system , they were not fitted as standard always an option , with a full blown system needing its own loom and sensors , or they were fitted aftermarket , was not very production friendly and much more costly up to £15-£20k for full system ,with commercially no benefit to Radical , and with Aim we were developing ‘plug and play ‘ type installation / upgrades.
So, the stack systems were fitted by folks who had invested in Stack and could move them from car to car as they bought new cars. There were very few specced like this and for uk / European championship eventually Aim was only system allowed.
The guys who were happy with Hewland and stack performance edge usually had a good amount of spares for both, so convincing them to ditch their spares as well as changing car was not easy.
Hence when I see a later car with Stack and Hewland it was usually special request not a variation back and forth in production.
Hope this helps, there are lots more stories in the development of SR8. It was nearly my nemesis!