I chose the OS 18 with the slide carb. They had them on ebay for $109. Ran it today and the RC magazines were right on! The OS 18 pushed it from around the stock set-up 40 mph to about 55 mph on the street. I am using the 14/17 pinion gears and the small diameter Proline Speed Hog II tires. I believe this is the limit on the outdrives and strength of the chassis. Looks like I will have to try the 10mm aluminum tube trick on the outdrives if the OS keeps producing this kind of power.