trappermike
ArboristSite Guru
The reed valve has many advantages over it's earlier piston-ported intake power.
Yamaha really pioneered reed valve intakes: piston-port reed intakes and had much success.
The reed valve has a much better intake-crankcase charge and timing than a piston port,and also has much better crankcase compression than a piston port. Of course we're talking modern hi-flow reed valves,not some Homelite XL-12 thing. Piston intake ports open at a way too late period,and close at a way too late period,but they can make great power. If only you could make an intake port open at the right time and close at the right time,well reed valves come close to that. Not only that the reed valve stays closed during the piston's downstroke to create more crankcase compression,there is much higher pressure in the crankcase to push gases up the transfer ports.They also create a much better intake period,almost ideal,a really strong well-timed intake charge of up to 180 degrees or more.. In piston port motors there may only be 30-40 degrees of crankcase compression when the intake port closes to push fuel up the transfers into the cyl.,whereas the reed motor has about 120 degrees compression on the crankcase-far more pumping pressure.
Of course to adapt reed valves to a saw you must use modern design,a big reed cage and well designed intake. With reed valves you can also use a larger carb than can piston-port and still run like stock.
Yamaha really pioneered reed valve intakes: piston-port reed intakes and had much success.
The reed valve has a much better intake-crankcase charge and timing than a piston port,and also has much better crankcase compression than a piston port. Of course we're talking modern hi-flow reed valves,not some Homelite XL-12 thing. Piston intake ports open at a way too late period,and close at a way too late period,but they can make great power. If only you could make an intake port open at the right time and close at the right time,well reed valves come close to that. Not only that the reed valve stays closed during the piston's downstroke to create more crankcase compression,there is much higher pressure in the crankcase to push gases up the transfer ports.They also create a much better intake period,almost ideal,a really strong well-timed intake charge of up to 180 degrees or more.. In piston port motors there may only be 30-40 degrees of crankcase compression when the intake port closes to push fuel up the transfers into the cyl.,whereas the reed motor has about 120 degrees compression on the crankcase-far more pumping pressure.
Of course to adapt reed valves to a saw you must use modern design,a big reed cage and well designed intake. With reed valves you can also use a larger carb than can piston-port and still run like stock.