pretty good
I have to say that you did a good job immitating the Mario Kart engine. Now you just need to put in more levels and other things that are needed to make those levels fun. For one thing, you should have actual walls. It's nice that there was friction, but the player should bounce off the walls subtly like in the original game. Also, power ups and obstacles can make the levels look good. Right now, the level looks bland. Also, put in sound FX. Aside from all of that, the engine is pretty good.