Hello all, and thank you for sharing your knowledge on this great forum.
My name is Steve and I live in Sarnia, Ontario, Canada. I drag race snowmobiles on both ice and grass. My current project is a 1047cc three cylinder, case reed induction, Suzuki engine, based on an Arctic Cat F7 two cylinder engine. 79.7 X 70 bore and stroke with auxiliary exhaust ports. After reading this thread it is obvious that snowmobile cylinder design is not at the level of today's best technology and I am hoping to rework a cylinder and start dyno testing. To that end, I need some clarification regarding the "Wobbly" exhaust duct. My thinking is as follows:
Raise the exhaust port floor to the point of effective transfer opening at the bore and then fill in the port floor enough to carry a 25 degree angle to the end of the spigot.
Weld and cut the duct roof at an angle greater than 25 degrees such that the area is reduced to 75 % of the original effective port area at the bore, at a length of 1.5 times the bore diameter 119.5mm.
Then cut the spigot roof at an angle of "X" degrees to achieve an opening of 100% of the original effective port area at a length of 2 times the bore diameter 159.5mm.
Is my thinking correct that all area changes are made by changing the angle of the duct and spigot roof, and the width of the complete setup is the same from the port to the end of the spigot?
If the above is correct is the transition from duct to spigot left sharp or radiused? If radiused, how much of a radius?
I can't seem to find much information with regards to the passages from the auxiliary exhausts. From the posted pictures, it looks like the passages exit the spigot at close to the horizontal centreline. Is the centreline of the spigot end the exit target or should these passages be ran at 25 degrees the same as the floor of the duct and spigot and exit wherever that puts them?
How is the sizing and the inward angle of the auxiliary passages determined? A semicircle equal to the height of the auxiliary port angled inward enough to still have the same semicircle at the end of the spigot?
Any and all help is appreciated.
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