Im buying a hpi mt racer that has a .12 O.S. cv-r engine. The seller says this engine is pretty difficult to tune and i am not very experienced. So i am looking at the HPI .18SS pull start engine. I have a .15 FE and it is reliable and easy to tune and thats why i want to get an HPI engine. Do you think this is a good choice? And if i were to sell the O.S. .12 engine, in good condish, how much do you think i could get for it?