We went with the 38mm APT SmartCarb for a few reasons. First of all, no more jetting. Also, APT claims that the SmartCarb has proven to provide a broader powerband in most applications both on the track and on the dyno. That being said, we took a step down to the 38mm instead of the 40mm so that the quad would be a little more rideable before hitting the powervalve instead of constantly being on the pipe. I'm pretty sure we're going to be the first to try this carb out on the quadzilla and I'm confident it is going to be a blessing over the stock 87 Mikuni, but that's not really saying much, LOL. I was looking to replace the reeds and air filter with fresh components before the carb came in so that everything around it was "clean" if you know what I mean. It wasn't in hopes of a performance gain at all. Just not sure how old the reeds in this motor even are because we haven't taken anything with a gasket off yet.