crazybond700 Posted May 4, 2016 Report Share Posted May 4, 2016 https://scontent-lhr3-1.xx.fbcdn.net/t31.0-8/q81/s2048x2048/13131628_10208548852892630_339939631488377412_o.jpg Interesting 1 Quote Link to comment Share on other sites More sharing options...
biffsgasgas Posted May 4, 2016 Report Share Posted May 4, 2016 Very! Whats going on under that thing... Looks almost 3d printed then cast. --Biff Quote Link to comment Share on other sites More sharing options...
cascao Posted May 4, 2016 Report Share Posted May 4, 2016 http://www.mototrial.it/sostenitori/mototekna/novita-2013/testa-regolabile.htm Quote Link to comment Share on other sites More sharing options...
smokey125 Posted May 4, 2016 Report Share Posted May 4, 2016 Very! Whats going on under that thing... Looks almost 3d printed then cast. --Biff Looks like it's just been fairly roughly machined on the outer surface. Interesting idea, don't really like it as it changes squish and compression, personal opinion is that a regular insert is best as you can maintain the squish gap. How often would you need the ability to change compression ratio like that? Quote Link to comment Share on other sites More sharing options...
zuendapp Posted May 5, 2016 Report Share Posted May 5, 2016 Years ago I did see a variable compression cylinder head for a Yamaha YZ250, The dome was preloaded for maximum compression and as the RPMs rose it would moved up into the dome for less compression. I believe it was made in Italy?? I searched for photo's on the net and could not find any. Typically higher compression is for more low end power and less compression is for higher RPM that a motocross bike might need. I like the idea of externally changing compression, I have seen problems with taking heads off with "O" sealing. Terry Quote Link to comment Share on other sites More sharing options...
crazybond700 Posted May 5, 2016 Author Report Share Posted May 5, 2016 A lot of people, especially in the UK mount flywheel weights, extra gaskets etc. this will definitly help (however probably be expensive?). The bike can be a powerhouse if needed, and otherwise be a little bit grippier and less powerfull. Quote Link to comment Share on other sites More sharing options...
dadof2 Posted May 8, 2016 Report Share Posted May 8, 2016 What actually counts is not so much the compression [ratio] as the mean effective pressure (MEP). The easiest and proven way of varying the MEP is by varying the ignition timing and the height and / or profile of the upper part of the exhaust port (power valve) The map switches on most trials bikes work by varying the ignition timing, but an even greater variation in engine characteristics could be achieved with an exhaust valve, but at the expense of added complexity and costs. Quote Link to comment Share on other sites More sharing options...
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