ORIGINAL: alangsam
if you race you need to use motors designed for starter boxes not pull starts. Yes pull starts and roto starts are easier than a Starter box. The engines are different. the RG's made for starter boxes have a little more compression and are more reliable. You wont find many competitive 21 racers using pull starters.
No the compresion ratio is the same. In fact everything is identical between the pull start and starter box version.