If you like Aurora A/FX cars I have written an article on tuning Magnatraction and X-Traction cars that has a lot of info that also applies to those.
https://drive.google.com/file/d/0BzLR42 ... sp=sharingIf the cars have sponge tires those really need to be treated with traction compound to run well. The tires tend to harden up with time and the traction compound will not be effective for very long. Most people avoid that problem by using slip-on silicone tires that work very well if the track is clean. The quick way to clean a track that is slightly dusty is to run around a car that has gooped sponge tires.
Aurora Magnatraction and first generation Johnny Lightning/Auto World X-Traction cars take the same bodies as A/FX cars and have a modest amount of magnetic downforce, you might try one to see how you like it. The latest X-Traction cars have an added neodymium traction magnet, in my opinion those are mostly for kids. In any case the extra magnet can easily be removed.
A/FX cars have been out of production since about 1974, you have to scour swap meets and ebay to find even used examples. New old stock T-Jets are still available, but that is not the case with A/FX cars, however you can build a NOS car using parts from places like JAG hobbies. Another alternative is to remove the tall magnets from a Magnatraction or X-Traction car and replace them with A/FX, Johnny Lightning or Dash magnets with shims under them.
You might also be interested in Gravity type cars, those do not rely on magnetic downforce, they are raced on both railed and braided tracks and tend to be much more sophisticated than the Super II type cars. There are several other slot BBs that cover the subject of Gravity cars, if you drop me a PM I can give you some links.