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DV,
I will have to agree that a spool will not work for autocross usage. However, for a high speed track such as RA, Willow, or Laguna Seca, they can be used fairly effectively.
A proper differential is superior to a spool in most all cases for road course work.
Unfortunately, all of the differentials that I have seen for a 9 inch rear as well as the 8.8 (Which is what is used in the JBL) have limitations as to setup and operation. (The exception is the McLaren electronic unit for the 8.8, but this is a very expensive unit and not a production item. This means they are build as bespoke units.)
The problem with all of the units (to my limited knowledge) is that they are not adjustable as to percentage slip in the deceleration mode. This is very critical in chassis setup, particularly in the case of a rearward weight bias chassis. This slip percentage is very critical to braking and initial turn in.
Of course the acceleration percentage slip is also very important for mid corner and exit. Current racing differentials will allow for changes in these settings to properly set up the chassis. I certainly wish that someone would make a proper unit for the 8.8 that was affordable and available.
I hope that some of the JBL folks will make it to your "Spring Fling" next year. However, they would all get hammered on an autocross type track with the standard setup. (The rack ratio is way too slow for tight autocross type tracks. As well, the standard dampers would probably have too much rebound control and the chassis would be sluggish in the weight transfer times required by autocross type tracks.)
Craig,
The major differences in setup will surprise you. Note: this is only for slow speed corners, you only change the damper settings on the high shaft speed control. (Not the slow shaft speed, which affects the high speed corners.)
More rearward brake bias and softer bump settings front, lighter rebound rear. This allows the chassis to transfer and rotate into the corner. However, one must pick up the throttle very early (Prior to apex) to catch the rotation. Once you get used to this, it is a quick way around and fun to drive. (Much like a shifter Kart.)
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