Four-Stroke Rule Change-Help!

KTMkarl794

KTMkarl794

PR Addict
I'm currently researching the history and future of two-stroke and four-stroke engine technology for school (only way I can keep myself motivated anymore is to some how relate the research to moto!). I'm having serious trouble finding the official rule book change for 1996 that allowed four-strokes with nearly double the displacement to compete in the 250cc class. Some sites say the change happened in 1996, others say 1998, but by 1998 Doug Henry had already won the Las Vegas SX on the YZ400. Anyone have any good links or knowledge on the topic? Not trying to start a debate between 2's and 4's but more so find a good medium of data.

I'm also looking to find any good research that has been done for the future of two stroke technology, in relation to EPA regulations and what not. KTM has been rumored to have a direct injection two stroke coming, can anyone confirm this?

Thanks Guys!
 
For current / modern two stroke info read up on Activated Radical Combustion and the EXP-2 two-stroke engine ….both were experiments at Honda.
 
I don't think it was an actual rule, but an exception given to the manufacturer's to experiment with the 4 strokes. They were allowed to run so many races at first to allow for testing.

Would recommend contacting the AMA office directly and let them know what your working on and see if they'll provide you with the information your looking for.
 
Greg Zitterkoph rode an ATK 604 at some open/500 nationals in the late '80s. Chuck Sun also rode a 4 stroke. I think it was a 650 Husky.
Doug Henry rode the YZ400 at the '97 Vegas supercross and won. He also raced the outdoor 250 series on it in '97. Poor guy broke his back at Budd's Creek in '95. In '97 at Budd's Creek the 4 stroke blew a motor over a double jump. Henry broke both arms. The next week, at the next national he was frantically waving and cheering teammate John Dowd from the pits. Henry won the Budd's Creek National and 250 championship in '98 aboard the first year in production YZ400.
 
Try posting this up in the forum of twostrokemotocross.com There is a seemingly endless knowledge base of everything concerning smokers
 
I believe what you are looking for is the homologation rule that allows a manufacturer to submit an application to race a bike that is not yet avaliable for sale. I think you have always been able to race a four stroke but the displacement limits have been adjusted several times to try and keep the playing field level. You can find some information in the Pro racing rules on the AMA site. Remember those rules are different from the amatuer racing rules also.

The examples listed above you also have to remember that the MX Pro Nationals used to have part of the season being run on 250cc machines and the other part on 500cc machines. I would assume the limit for the four stroke displacement would have been adjusted also.

I would try emailing the AMA also they would probably be able to supply you with more specific times and the actual rules for the different times.
 
From what I've been reading, Ski-doo already has 2 st DI technology that is now pushing 4st engines into the dustbin of extinct engine designs!
Read reviews of the new 800....
-TJ
 
i own a model year 2001 50cc 2 stroke aprilla scooter with with efi & it will smoke most other 50cc scooters (zumas)
 
Gary, bring your Aprilla down to Beans sometime next year and I'll race you with my Zuma. Anyone else with a 50cc scooter would be welcome too. No big bore kits though..
 
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