Only you can decide what lenses to use, since only you know the track where you will be photographing. If it's a club race meeting, your chances of getting a track pass should be better, which on some tracks means you could get good close-ups of cars at race speed with a 100 mm lens (!) - conversely, at an international meet where you can't get close, a 400 or 600 would be vital.

I would think your present gear would be quite good, as long as your zoom is sharp enough at full aperture. For most peole these days, b+w is traditional in itself, I wouldn't worry about darkroom tricks, personally I wouldn't even push-process the film. If you do buy another lens, why not look for a 400 - there are some around with no automatic diaphragms but good glass available for peanuts (you don't need an automatic diaphragm because you'll be shooting at full aperture all the time!).

Regards,

David