secsy1 Posted 3 hours ago Report Share Posted 3 hours ago In Poland apparently they use R500 engines that are restricted to 250cc to save costs as the engine is then unrestricted and used as a 500cc. Can anyone elaborate on this and how specifically the engines are restricted? Quote Link to comment Share on other sites More sharing options...
phillwhitewasmad Posted 3 hours ago Report Share Posted 3 hours ago 54 minutes ago, secsy1 said: In Poland apparently they use R500 engines that are restricted to 250cc to save costs as the engine is then unrestricted and used as a 500cc. Can anyone elaborate on this and how specifically the engines are restricted? Its through an insert in the carb and inlet manifold to reduce the fuel flow from 34mm down to about 28 or there abouts it is becoming a class in the uk next year Quote Link to comment Share on other sites More sharing options...
piston197 Posted 1 hour ago Report Share Posted 1 hour ago 1 hour ago, phillwhitewasmad said: Its through an insert in the carb and inlet manifold to reduce the fuel flow from 34mm down to about 28 or there abouts it is becoming a class in the uk next year The CC is worked out on bore and stroke, even if you sleeve down the inlet manifold the bike will still be a 500cc albeit with less power, you would need to sleeve the cylinder bore and fit a smaller piston to produce a 250cc engine, much like Matchless did in the day, the 350 Matchless and 500 matchless single had the same stroke, but the 350cc had a 69mm piston and the 500cc had a 82.5mm piston Quote Link to comment Share on other sites More sharing options...
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