A SP has better low end torque....just what a bus needs. A DP has better top end....just what a light beetle needs. In the USA, 71 buses were the last of the upright 1600's. They were SP..... > I see all this talk of converting from DP to SP. I hope this is not a stupid > question but why would one want to convert from DP to SP. I always thought > that DP was an improvement over SP.