2 stroke transfer port angles

[Bummers]

Has anyone got any information on the effects of different angles of the
roof of a 2-stroke transfer port has on performance? That is, the
vertical angle at which the fuel enters the combustion chamber.

Is there an ideal angle for max horsepower? Are there any trade offs?

It's tuning time for the 1975 rotary disk valve Kawasaki KX125.

Bummers

[IRONDOG]

Post by Bummers
Has anyone got any information on the effects of different angles of the
roof of a 2-stroke transfer port has on performance? That is, the
vertical angle at which the fuel enters the combustion chamber.
Is there an ideal angle for max horsepower? Are there any trade offs?
It's tuning time for the 1975 rotary disk valve Kawasaki KX125.
Bummers

Poke around this site for some answers: http://macdizzy.com/
Jerry

[Bummers]

I've been there - a great site but I didn't find a lot of info on the
effects of different transfer port roof angles.
It seems the general consensus is "flatter is better".

Post by IRONDOG

Post by Bummers
Has anyone got any information on the effects of different angles of
the roof of a 2-stroke transfer port has on performance? That is, the
vertical angle at which the fuel enters the combustion chamber.
Is there an ideal angle for max horsepower? Are there any trade offs?
It's tuning time for the 1975 rotary disk valve Kawasaki KX125.
Bummers

Poke around this site for some answers: http://macdizzy.com/
Jerry

[FB]

Post by Bummers
I've been there - a great site but I didn't find a lot of info on the
effects of different transfer port roof angles.
It seems the general consensus is "flatter is better".

That makes sense if the strategy is to direct the flow of fresh mixture
toward the rear of the cylinder instead of just aiming it up where it
can short citcuit out the exhaust port.

If you aim the flow toward the rear, it can bounce off the back of the
cylinder and be turned up, and then sweep across the combustion chamber
and drive burnt mixture out instead of short circuiting.

Tuners used to avoid messing with the top of the transfer ports. They
didn't want to upset the scavenging loop. They would make an aluminum
spacer to fit under the cylinder, raising the exhaust port.

They would mill a thickness equal to the spacer and an extra base
gasket off the top of the cylinder block to keep the compression ratio
the same.

Then they would grind on the bottom of the exhaust port and the bottom
of the transfer port. That way, they increased port area without
changing critical angles developed by factory testing.