old bob at herne bay 828 Posted March 22, 2021 From Flemming's website (courtesy of Google Translate The Dane Flemming Graversen, currently one of the most sought-after tuners in the speedway scene, is now coming onto the market with an in-house design: a DOHC cylinder head for the short-stroke GM engine. The aim of this new design was to achieve a higher torque in the lower speed range in order to improve the acceleration after the start. Therefore, the maximum speed is only 11,000 rpm. but an increase in performance between 2 and 3 hp compared to the series was achieved. The camshafts are driven by 2 chains, whereby the chain coming from the crankshaft drives the inlet camshaft and a second chain then branches off to the exhaust camshaft. The camshafts are mounted on one side in needle bearings and on the other side in ball bearings, which keeps friction losses low. By using light metal materials with very low weight and machining with the latest CNC milling technology, the weight of the The complete engine, as offered by Graversen, weighs 27.2 kg, only about 1.2 kg more than the production GM. As is usual with four-valve engines, the spark plug is placed exactly in the middle of the combustion chamber. The inlet valves have a plate diameter of 34 mm and a shaft diameter of 5 mm. The plate diameter of the outlet valves is 33 mm and the shaft diameter is also 5 mm. The valves face the combustion chamber at an angle of 22 °. So he has built a completely different cylinder head (double overhead camshaft ) completely changing the characteristics of the original GM, but re uses the the GM "bottom end" ? Lots of tuners have done his in the past ... adding new top ends to existing bottom ends. So don't see an issue. Sounds like GM need to step up and offer thier own dohc motor ? 3 Share this post Link to post Share on other sites
uk_martin 1,606 Posted March 23, 2021 Didn't Weslake have a DOHC engine out in the 1980's? It never really caught on did it? From what I remember riders always thought that the SOHC was a step up in complexity from the pushrod 2-valve JAWA's and didn't want to take another quantum leap forward in complexity (& consequent cost) . I wonder how it will pan out this time. Share this post Link to post Share on other sites
Sings4Speedway 3,247 Posted March 23, 2021 7 minutes ago, uk_martin said: Didn't Weslake have a DOHC engine out in the 1980's? It never really caught on did it? From what I remember riders always thought that the SOHC was a step up in complexity from the pushrod 2-valve JAWA's and didn't want to take another quantum leap forward in complexity (& consequent cost) . I wonder how it will pan out this time. From more recent memory didn't jawa release a demo DOHC engine that was being backed by Sam Ermolenko? All went quiet after they were found to be wildly oversized? Share this post Link to post Share on other sites
Technik 491 Posted March 23, 2021 The Jawa DOHC unit was very top heavy & did'nt suit the more light weight riders. 2 Share this post Link to post Share on other sites
Daniel Smith 5,666 Posted March 23, 2021 6 hours ago, Technik said: The Jawa DOHC unit was very top heavy & did'nt suit the more light weight riders. Wasn't the other issue that the tracks had more shale than today & rider's couldn't stop the engines spinning to hard & couldn't never get the setups right between tracks?? Whereas today, this idea may now have substance with a better pull at the low end on today's super slick circuits?? Share this post Link to post Share on other sites
IronScorpion 1,407 Posted July 14, 2021 Is any one using the Flemming Graversen top end or is the dispute still ongoing in what riders can use? I have not seen any pictures yet of riders using it & thought it would be more suitable to the British tracks over the Swedish or Denmark tracks although I have no knowledge of shape or size of tracks in those 2 countries. Share this post Link to post Share on other sites
