Not hitting the wall is much more important than the motor. I hear people talking about this or that and then watch them run they smack the wall ten times in a 6 minute heat. You want to improve in VTA run 6 minutes and the body doesn't have one scratch (Not one). If you can do this you will be in the A main and 90% of the time in 1st place.
When you run at my track the winner is the one who hit the wall less than everyone else. If you look at in this manner you'll realize motor and new chassis and etc... isn't that important. I've raced Batman and neither of us hit a wall or each other in a heat. When you come off the drivers stand knowing this you're pumped even if you ended up second. It's a feeling you don't forget.