Port Ponderings

[2strok4fun]

I have my watercraft cylinder out now for some freshening up and other goodies. This is a steel sleeved motor with a displacement of 476.62cc x 2. While looking at the stock port layout and the entry angles, I notice the entry angle has a multiple angle, the sleeve and the casting have different target points. The front wall of the main xfer has a "kicker" with the sleeve pointing its target point directly to the rear of cyl/boost port. The front wall casting has a more typical target of approx 55% of bore. Also the back wall has a kicker trailing away to the rear of the cylinder as well. There are many people that are doing big bore on these motors going from the standard 88mm bore up to 92mm. This virtually removes the kicker. I think the possible downside to this is more short circuiting of charge. The charge short circuiting is my guess as why the cylinders may have the kicker for emission purposes.

I was thinking of changing the angle on the kicker without doing the big bore, by either grinding, which would increase the area, or by using epoxy. Shouldnt a target area more toward the center of the bore raise peak HP? What are your thoughts?

 

[Eric Gorr]

I know what you're describing and I suggest using epoxy to match the duct to the sleeve in the transfer ports. Don't touch the rear boost, it should be 1mm lower than the other transfers. Raising the transfers on a PWC tends to kill the low end and make them lazy getting up on plane.

 

[2strok4fun]

So should I match the angle of the casting wich points it to the 55% of bore, average the two with a straight fill, or just match to reduce the "kicker"?

I understand about not raising the the xfers, I have lowered slightly by using a thinner base gasket.

This winter I will prolly pick up some cyls off of e-bay to try some other porting, one idea I have is to change the vertical entry angle of the secondary xfer port, currently has a 0 angle, I am thinking of making the entry angle 2 deg by using epoxy to not raise the xfer port. What do you think?

Thank you for your response.