Rotary Spark Gap, the rpm's, and horsepower

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <JACKBINTHEBOX-at-aol-dot-com>

First of all, I'd like to say thank you to all of you who answered my 
previous posting about splicing two secondary coil wires together.  I will 
be cutting my 4 foot secondary in half, and I guess I'll be making another 
tesla coil with it soon!  Many thanks, you'all saved me from disaster.

I will be making a RSG, but I don't quite understand the significance of 
motor RPM's and horsepower in the design.  Is it better to have more or 
less RPM's and horsepower?  I have a whole bunch of 1/20 HP, 3600 RPM 
motors from film projectors.  Would one of these be suitable for an RSG 
with like a 6" disc?  I see that most of the professional RSG's have huge 
motors attached (1/4, 1/2, or 1 HP), but the RPM's are usually only like 
1800.  Why is it necessary to have so much power and so little RPM's?

Many thanks,
Jack