becuase a thermo fan costs a lot more to manufacture than a engine fan...

also an engine fan is more reliable becuase it has no moving parts or electricals

but as was said the thermo can be swiched off and that is where the power advantage is

from experience in playing with 4x4 you can get a range of fans for bigger motors and putting one that has more blades seriously affects power and revability... so if thats noticable then there should be gains to have on our smaller scale


getting back to topic.....

electronic ignition is one i forgot... best to get an elec dizzy for ease and tidiness... but they arnt particularily easy to get

p.s. i just noticed the stuff about ceiling fans.... i would love to see you try to stop one spinning at 3000rpm...(no i wouldn't)