Terry Syd
Addicted to ArboristSite
Transfers
If I had taken it too far, a new piston would fix it right up - I have been trimming the crown of the piston in front of the exhaust port. Actually, this 158 degrees exhaust timing (from 12 degrees blowdown to 16 degrees, a 33% increase) feels about right. There is a noticeable torque increase in the upper revs where the saw likes to sit and cut.
To properly raise the transfers on these Husky stratos would be a real job. On these Huskys there is a transfer cover that has an insert into the port that directs the flow. Essentially, you can't raise the transfer without stuffing up the flow characteristics. The transfers are already sitting quite high (126 degrees duration) and it is the small blowdown time that limits the power.
For someone who doesn't want to take a Dremil to their jug, just nipping two degrees off the crown next to the exhaust port and trimming the intake skirt to 150-154 degrees duration would probably be an easy performance mod that anyone could do. It would also still retain the stock cylinder liner at the top of the exhaust port for long cylinder life. The purists on the board would consider it a hack job, but for someone who just wants some more power out of their saw it would be a quick and easy mod that they could easily reverse by purchasing a new piston.
I think I will find someone to build me a dome on a new piston. The 4 degrees I added to the blowdown has taken a bit more off the front of the piston than I wanted and is trapping some mixture under the squish band that I could be using for better power. The first trimming of 2 degrees was very small and likely not trapping much mixture (or perhaps just air as it is a strato) and I would consider it a negligible loss - especially since the extra blowdown time made such a significant difference.
If I had taken it too far, a new piston would fix it right up - I have been trimming the crown of the piston in front of the exhaust port. Actually, this 158 degrees exhaust timing (from 12 degrees blowdown to 16 degrees, a 33% increase) feels about right. There is a noticeable torque increase in the upper revs where the saw likes to sit and cut.
To properly raise the transfers on these Husky stratos would be a real job. On these Huskys there is a transfer cover that has an insert into the port that directs the flow. Essentially, you can't raise the transfer without stuffing up the flow characteristics. The transfers are already sitting quite high (126 degrees duration) and it is the small blowdown time that limits the power.
For someone who doesn't want to take a Dremil to their jug, just nipping two degrees off the crown next to the exhaust port and trimming the intake skirt to 150-154 degrees duration would probably be an easy performance mod that anyone could do. It would also still retain the stock cylinder liner at the top of the exhaust port for long cylinder life. The purists on the board would consider it a hack job, but for someone who just wants some more power out of their saw it would be a quick and easy mod that they could easily reverse by purchasing a new piston.
I think I will find someone to build me a dome on a new piston. The 4 degrees I added to the blowdown has taken a bit more off the front of the piston than I wanted and is trapping some mixture under the squish band that I could be using for better power. The first trimming of 2 degrees was very small and likely not trapping much mixture (or perhaps just air as it is a strato) and I would consider it a negligible loss - especially since the extra blowdown time made such a significant difference.