Not much! I had such a great season that I`m reluctant to change anything, so I`m not. The motors coming out to check the bearings and valve springs and do a leak test as it has 500 runs on it now if everything looks good it goes right back in. I just picked up another 904 to be built as a spare, the convertor was freshened by Ultimate last winter and I have a fresh set of QTPs I only used at the Bracket Finals ( less than 10 runs) so there fresh for next year. Since I race my D150 on occasion I need a set of wider rear wheels and a stickier drag radial type tire. The Pep Boys tires I have don`t hook very well even a 20 lbs. the truck only runs mid 15s but I lost a race last week because I spun a little.