TryHard

iTrader: (4)

3x6 I think, but 3x8 works fine as well.

Normal CVD's have a limit to the working range of the angle they can turn. This is because they are not a true CVD (the CV part refering to constant velocity!), so the driveshafts speed up and slow down very quickly during their rotation. At high steering angles, this is what creates the chatter common on the front.
If using a diff or one-way, its not noticeable, simply as the velocity differences between the outdrives is compensated for by allowing one side to spin faster than the other. The effect is still there however.
However, with a Spool, the outside wheel is going to spinning at the same speed as the inside wheel, and everything is bound together. This acts to amplify the effect of any chatter, especially at high lock.

The DCJ/ECS/LCD (Losi were the first with it for their JRXS) is still not a true CVD (look at the litemodz CVS for one of those, if you dare), but reduces the angles that the driveshafts see in operation. By effectively halving the maximum angle, it drops the joints back into a reasonably effective operating range, reducing chatter.

So why does it help? Simple... Chatter can (as has been disscussed recently here, with Nilks' question) cause the front end to bind up, and "jump" when cornering. If the inner wheel is spinning faster than traction allows (as happens with a spool), and then there is bind up because of the CVD angle, there will be a sudden loss of grip... which if your using a high lock angle, your most likely in the middle of a corner, so it happens at the point where you least want it too!! This is why the cars tend to "wash out" from the apex at higher steering angles.
Using the DCJ's should help to stop this, in effect increasing steering in the middle of the turn. Should make the front smoother as well, and reduce the spool effect.... in theory

HiH
Ed