During braking the slapper bars will dive toward the road and not really help in wheel hop. They use to make a shorter traction bar called Traction Action Jr. This style device clamped on the front of the leaf spring with U bolts. It made the front of the spring ridged and kelp the spring from S'ing. This style helped wheel hop some during braking.
Going back many (won't say how many) years, guys used to make traction bars from old tie rods. Mount a bracket under the axle and another even with and below the front spring mount, put a tie rod end on each end of a heavy truck tie rod and they had traction bars. They seemed to work quite well for both launch and braking but I haven't seen any like that lately. Anyone still doing that? Advantages/disadvantages. Maybe not strong enough for today's engines, tires, etc?
Caltracs look just like the ones in Frank's link. Only difference I can see right off is Caltracs have 2 different holes on the front bracket to mount the front Heim joint, and Calvert ships out a solid aluminum front bushing for the eyes in the spring, so there is no twist or flex at all at that front portion where it mounts to the car.
I have the competition engineering slapper bars on my car. If you have a set of scales and have someone who knows how to use them you can make them work really good. My engine builder had a camaro with slapper bars on it and it ran mid 9's at 3600 lbs. with a dot tire. My car 60 ft.'s in the mid 1.30 's and runs high 10's for now and I don't have any plans of changing them! And as far as braking it may be the shocks you want to play with.
Do you have the universal fit or the J bolt design? Mine are the J bolt design that are for the 65-73 Mustang. The car needs to be scaled to get them right. Just don't be one of the people with their bars hanging 2" below the leaf spring! They will be touching the spring at the front. You just need scales to tell you how much to preload to get your corner weights evened up. Remember your car works in an X shape so changes made to the left front will affect the right rear. This includes shock settings, tire pressure, and front end alignment. If you don't have scales it's really just trial and error. Also make sure the car is tracking square by measuring the wheelbase on each side.
