The new fantoms are great engines. The 2005's arent as cheap to rebuild as the previous versions. Previous engines by fantom costed around $35 for a piston and sleeve set and the 2005's cost $55 now. Depending on where you race I would go with the fantom or something with a little more power than the cvr. It is a great off-road engine but if you are on a bigger track you won't be able to keep up down the straight. Rotary carbs tend to be better for most drivers for off-road, how ever I run slide cause I like the driving feel of it. Rear exhausts have more low-end power than a side-exhaust would.