Best thing is to take a look at the rulebook first for the class you intend to run. Or check it out to decide a class where you want to run and build from there. Generally .21 top fuel cars are 29 inches have to weigh 40 some odd ounces and have a .21 motor modded or not doesn't matter. Brakes and a throttle return spring. Check www.imdra.com for the current rulebook. I had a couple of LiteSpeed rails. One was the X-21 and I upgraded that to a BioHazard. Lots of fun to run. Lots to learn to make them go fast. Direct drive cars are the deal right now. Basically a truggy rear gearset with an adapter so the clutchbell can accept a dogbone type driveshaft direct to the rear wheels. No tranny single speed. Gets rid of a lot of rotating mass to ditch the jackshaft and tranny cluster. Clutch tuning becomes more critical when you are running direct drive. You don't have a lot of gearing choices with a direct drive car as you are using the final drive only. Some use the entire plastic diff carrier some make custom mounts and run the rear pinion and bevel gear out in the air without a case around them. Brakes on those cars need to be on the rear axle so if you break a driveshaft or clutch you can still stop the car.

Griz