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!).