Pros Of The 4 Stroke Engine

Well, since the YZ400F made its debut in 1997, when Doug Henry won the final supercross of the year in Las Vegas on one... things have changed dramatically. The fours have fast become the dominating force on any track or terrain. Why? Well it seems there are a number of debatable reasons. Their power to weight ratio is almost on par with the 2 strokes - and I simply mean in terms of how a 450cc four stroke is now a lot closer to the weight of a 250cc two stroke, but puts out a similar amount of speed and power. Back in the early 90's four strokes were heavy beasts and were considerably slower than the two's. With the new and improved 4-banger, many people find them easier to ride with their smooth, tractable power delivery. But on the other hand, a lot of riders don't actually want that. They want the thrill, noise and adrenalin of a powerband that only a two stroke can serve up.So why are the 2 strokes disappearing? Some people believe (and blame) the format of the AMA, and large companies such as Honda have a heavy influence over why we are witnessing the decline of the popular two's. Is it fair that a 450cc four stroke is able to compete against a 250cc two stroke? It has also been said that another contributing factor to the 2 strokes decline is the pressure felt by government groups and lobbyists to phase them out because of the environmental damage they cause. But how much more pollution do they really put out compared to the 4's? It seems that the technology already exists to create a two stroke engine that is just as, if not more environmentally sound as a four stroke.

http://www.dirt-bike-tips-and-pics.com/2-stroke-vs-4-stroke.html
http://www.btosports.com/p/PCTI4R4
http://blogs.internetautoguide.com/6564865/auto-news/2010-honda-crf450r-dirt-bike-available-now/index.html

A Honda CRF450 2009 at Washougal MX Park.

This is a Procircut pipe for a 4 stroke engine and bike.