Join Date: Aug 2011
Location: Richardson, TX USA
The radial valve layout does not actually refer to a difference in the valves themselves, but the way they are positioned in the cylinder head. This arrangement allows improved port size and shape, valve included angle, and improved combustion chamber shape. It may also contribute to better cooling. The main benefits are better breathing and better combustion efficiency, leading to better power output. This is extremely important in a short-stroke engine design, because there is very little stroke length to draw-in the intake mixture, or to push-out the exhaust gases. So breathing capability is paramount. As we know, the MV engine is the shortest stroke 750cc 4- stroke motorcycle engine ever made. This short stroke contributes to the high-revving abilities of this engine, and in a design like this, revs mean power. At nearly 14000rpm there is an extremely short time for the mixture to enter the engine, so the flow rate must be maximized. The radial valve layout is an effective way to maximize the flow, and improve the efficiency of the combustion by better chamber shape so that the fuel can be efficiently transformed into power at the high revs that are seen in this engine. With short- stroke designs, there is little inertial mixture flow to aid in the induction of the mixture beyond the BDC point of the stroke. Even with longer duration of the cam profiles, it hasn't enough time to keep drawing much after BDC. So it all must flow in on the initial draw of the descending piston. Anything that can be done to improve this initial mixture flow will do a lot to help the power output. Having the added benefit of better chamber shape, with less valve area being shrouded by the chamber walls and cylinder walls gives us the second benefit of getting the best burn out of the additional mixture that has been inducted into the cylinders. Then the radial layout of the exhaust valves has a similar effect in getting the exhaust gases out of the cylinder. I am not certain, but I believe this was first done in some Ferrari F1 engines. As we know today's MV 4-cylinder engines were derived from a Ferrari F1 engines in the early 90's.