ESE's works engine tuner

[jamathi]

So here is the result of doing the opposite to having a hot exhaust duct.
I drilled thru the holes from the watercooled case, up underneath the Exhaust duct,and moved the main water inlet to the cylinder
from over the Exhaust port, around to the inlet, allowing cold water to flow directly over the transfers.
Simple mod - 1 Hp, and no sign of deto as the datalogger showed under 1.5V
Thankyou Mr Dyno.

Thank you very much for doing this test.
It confirms my own experience.......
more power and less deto!
My compliments!

[F5 Dave]

The stock KZ10C engine has all the water flow into the cylinder from one side directly over the top of the Exhaust duct.
Here is the flow as I did it - see the plug up high on the side of the cylinder.
There are also two small holes drilled right thru to water in the case, that lets cold flow run directly up under the Exhaust duct.

Case like an old suzuki but with main at rear. So under and over duct important.

[Martin1981]

coating it will likely need new pipe dimensions in my opinion.

Different pipe dimensions wouldn`t be a problem for Wobbly i guess. The test only shows, what Wobbly and Frits told many times.

If the pipe was sucking exhaust gas out of the cylinder only, a coated duct could do something good or at least nothing bad maybe. But there is also fresh charge entering the exhaust duct. And this fresh charge "plug" is later pushed back in the cylinder again by the pipe. And this plug should be well cooled to make the engine make power and not detonate (The same situation as the exhaust gas entering the crankcase by the transfer ports and causing overheating and deto). So the duct should be flown around with water instead of beeing coated. So to speak, the (well cooled) exhaust duct is the intercooler of a 2 stroke engine.

[ken seeber]

So to speak, the (well cooled) exhaust duct is the intercooler of a 2 stroke engine.

Nice analogy.

[lodgernz]

In all the photos I have seen of disc valve setups, I've only seen one with a trapezoidal shaped inlet port.
Such a shape would seem to offer the least radial angle for a given port area, thereby maximising the fully-open period of the valve.
People who know stuff, like Jan with Aprilia, didn't use this shape so clearly there are issues with it.
Perhaps because the valve would open instantaneously rather than progressively. Closing would still be progressive but rather sudden at the end.


Anyone care to comment?

[TZ350]

Suzuki and Kawasaki have both made rotary valve ducts like this.



They become increasingly trapezoidal shaped as you widen them to get more flow area.

Bell or was it Jennings talked about the benefit to wave action of having an abrupt opening/closing. Tried it but not convinced myself, preferred the results I got with a gentler opening/closing and the wear on the closing edge, engine side was less.

[SwePatrick]

In all the photos I have seen of disc valve setups, I've only seen one with a trapezoidal shaped inlet port.
Such a shape would seem to offer the least radial angle for a given port area, thereby maximising the fully-open period of the valve.
People who know stuff, like Jan with Aprilia, didn't use this shape so clearly there are issues with it.
Perhaps because the valve would open instantaneously rather than progressively. Closing would still be progressive but rather sudden at the end.


Anyone care to comment?

I would imagine that in the short inlet tract you don´t want a lot of difference in shapes from the carburetor.
Any altering of the shape robs energy from the atmosphere to fill the crankhouse.

Rgds.

[husaberg]

I would imagine that in the short inlet tract you don´t want a lot of difference in shapes from the carburetor.
Any altering of the shape robs energy from the atmosphere to fill the crankhouse.

Rgds.

The idea behind the rectangular/trapizoid port compared to a true round port is that for the same number of open degrees you gain significantly more time area. ie it is open wider for longer. You achieve similar gains from a larger disc valve. (But with a larger valve you also gain a staighter inlet port as well)
Losing energy? The track needs to change from the carb to the disc port shape regardless.

Frits or Jan will explain the rounded corners but i think it was to do with boundary flow.
First pic is RSW125 (2nd 3rd appear to be from a similar year twin ) next one is an older version of Rotax.
The last Frits and Jan can explain the advantages of the shape. But i suspect it opens fully faster for longer time area.
Regardless the intakes clearly worked better with the edges slightly rounded but the port squared off.

[TZ350]

I would imagine that in the short inlet tract you don´t want a lot of difference in shapes from the carburetor.

Maybe True, but achieving it, is not so easy .....

And maybe not so much of a problem, a short tract may become virtually invisible and it basically becomes a carburettor attached to a window on the side of the crankcase. The carburettor and window have to both be big enough to pass the required amount of air/fuel mixture in the time available and remember the carburettor is open for longer than the window.

[Frits Overmars]

Bell or was it Jennings talked about the benefit to wave action of having an abrupt opening/closing. Tried it but not convinced myself, preferred the results I got with a gentler opening/closing and the wear on the closing edge, engine side was less.

You can forget about wave action in the inlet tract. The inlet is open during more crank degrees than the exhaust port, so for a wave to travel up and down the tract once, that tract should be longer than the exhaust pipe (OK, the speed of sound in the inlet tract is lower because it's colder there, but anyway..)
A wave would travel up and down the usual inlet length so often between inlet opening and closure that it would have lost all of its energy by the time the port closes.

You want to open the inlet when there is no pressure difference over the disc. Opening it any earlier would cause pressure loss from the crankcase, and opening it any later would cost time.area and cause an unwelcome drop in crankcase pressure that would slow the transfer flow down.
The only benefit of a late opening is that the pressure difference will send a clearer signal to the carburetter.

I would imagine that in the short inlet tract you don´t want a lot of difference in shapes from the carburetor. Any altering of the shape robs energy from the atmosphere to fill the crankhouse.

That's it, Patrick. Any change in shape should be gradual, but you don't want a long inlet tract either, so you must compromise between a trapezoidal shape and a short tract.

The track needs to change from the carb to the disc port shape regardless.

Not necessarily, Husa. I'm curious about your view.

The last Frits and Jan can explain the advantages of the shape.

I can't; you'd have to ask the Great Leader; he insisted on that 'nose'.

[husaberg]

Not necessarily, Husa. I'm curious about your view.

It was the same as yours a compromise over the shortest possible area to blend the shape from the carb bore to the intake port windows greater area.
If you were meaning the rounded corners i would suspect it is the same as having the edges on the ports slightly radiused.
plus square bore carbs are not that common plus a small round intake window in the cases would be bloody restrictive.


The Kawasaki one (pictured below)actually has back cuts incorporated into the short track, whether this is a production compomise or design feature i am not totally sure.
But it would be nice to suspect its the later.
TZs pic shows these back cuts on the Kawaski 175 valve.

I can't; you'd have to ask the Great Leader; he insisted on that 'nose'.

Funny.........

maybe his thoughts were to keep the port open in one area of the port on initail opening?

Or maybe he was a control freak who had been given the keys to the factory soley based on taking the credit for others work efforts at Cagiva?
I did notice the RSA125 has a few totally different discs. but thought that was due to the different orientation of rear disc engine.

[lohring]

Model engine disk valves always have a trapezoidal shape. However, they are confined to the crankcase diameter so need all the area they can get.

Lohring Miller

[SwePatrick]

This is a carb from PVP kart engine.



They start to alter the shape already in the carb to make inlettract flow more.
This to gain flow without having a to big area, this gains airspeed that overcomes pressure inside the crankhouse better at the late phase of filling the crankhouse, less 'spitting' backwards.

[lodgernz]

The last Frits and Jan can explain the advantages of the shape. But i suspect it opens fully faster for longer time area.

If I remember correctly, Frits or Jan stated that this disc shape was to give better support to the disc as it passed the port.
But my memory is pretty shit so I'm probably wrong.

[wobbly]

During my time at ZipKart, tuning for Hines Superkart Rotax 250 twin, we tested the rotary valve shape and the port shape to death.
The big issue with the trapezoid port shape is that the inlet column pressure on the disc wore away the closing side of the case really badly, really quickly.
The disc shape with simple opening/closing edges that were angled directly thru the crank center line worked just as well as any other, but the ones we developed
that were like the odd angled Aprilia version, reduced the wear even more with an oval port and lost no power.
We tried concave and convex opening/closing edges as well ( same timings of 140/88 ) with no gains.
I never quite managed to equal the full trapezoid shape power ( slightly better around and after peak ) but we simply could not stop the case wear issue even with
PTFE coatings and lube cutaway slots etc.