[Jeff Lee]

AFCO offers two unique valving specs that are an option. BNC & BNR. Stands for Bull-nose Compression & Bull-nose Rebound. You would use BNC on the front and BNR on the rear. What that means is the initial hit on either compression or rebound is very solid and less so a as the shock goes through it's travel.
I just had my 4 AFCO's revalved to this but have yet to run them so I can't say if it's worth doing. I also had the rear valving stiffened up considerably from what was offered initially. But keep in mind I'm a stick racer.
Opposite of what Rod stated earlier, I will be running a light spring on my rear coil-overs. That allows you to pre-load the spring to get the ride height and when you launch that stored energy is put to use. Rod having the shocks in front of the rear may have something to do with this as there is less leverage working the shock / spring.