my friend the pros use .21 engine
if you look @ the results always is .21
i have try everything
and o.s engines are the best

o.svspec its a very good engine for the price i like my vspec eb modified its other thing
the speed its the top of the line bit is more expensive


and the ninja jx.21 its the best of both worlds o.s made them for mugen thats on my truggy
better than a vspec similar power but whith o.s speed quality inside and 300 bucks no other engine @ this moment can compete whith the ninja
good luck buy vspec or ninja

i whant to try the new reedy and the team orion alpha engines but o.s power the best out there