ESE's works engine tuner

[wobbly]

The only logic I can muster re the transition taper , is that when the floor is colinear the returning wave front easily ramps up the reverse ski jump and arrives early , with maximum
amplitude whilst the piston is still low over the port - just after BDC.
Thus more of the finite plugging energy is seen at the port face , with the least interference from the rising piston.

[TZ350]

Dane Rowe

https://rocinantemecanico.blogspot.c...with-dane.html

TZ750. One of Rudi and Danes chairs.

[Pagi]

The only logic I can muster re the transition taper , is that when the floor is colinear the returning wave front easily ramps up the reverse ski jump and arrives early , with maximum
amplitude whilst the piston is still low over the port - just after BDC.
Thus more of the finite plugging energy is seen at the port face , with the least interference from the rising piston.

Does your exhaust duct is still relevant ? ( except perhaps the percentage of surface of the exit of the conduit as you specify it in a previous message). Have you or can you give us more details on the dimensions of the reverse ski jump ?(length, angle)

[Vannik]

Does your exhaust duct is still relevant ? ( except perhaps the percentage of surface of the exit of the conduit as you specify it in a previous message). Have you or can you give us more details on the dimensions of the reverse ski jump ?(length, angle)

Latest picture:



Wobbly can comment further.

[Pagi]

Latest picture:



Wobbly can comment further.

thanks Vannik....

[Kickaha]

TZ750. One of Rudi and Danes chairs.

TZ750 ? are you sure about that because I didn't know Yamaha made a triple

[TZ350]

TZ750 ? are you sure about that because I didn't know Yamaha made a triple

You are right. After a better look I now think it was a TZ350 with an extra cylinder added.

https://www.flickr.com/photos/teamhe...th/2966770061/

The days when someone with talent, energy and a modest workshop could build something to compete on the world stage with.

[wobbly]

Only thing to add is the ideal port exit roof angle has been found to be 25* , and the ski jump floor should be perpendicular to the bore then turn down , such
that the main duct smallest CSA is coincident with the increase in area created by the Auxiliary ducts entering from each side.

[katinas]

You are right. After a better look I now think it was a TZ350 with an extra cylinder added.

https://www.flickr.com/photos/teamhe...th/2966770061/

The days when someone with talent, energy and a modest workshop could build something to compete on the world stage with.

Very nice photo album collection. And nice short message from Dane's daughter Karin Hasen: Dane Rowe (Kurth) is my mum. She‘s not on facebook (she thinks facebook is evil) she‘s still alive and kicking and says „thank you for the nice comments“ and „I am very busy with ancient coins these days“

Add Yamaha TZ 525 triple. Maybe have been ridden by Gene Remero.

[Pagi]

Wobbly, thank you for the clarification

[Kickaha]

You are right. After a better look I now think it was a TZ350 with an extra cylinder added.

Apparently one of the first people to do it, I was already well aware of Rudy and Dane, he built some interesting stuff

[Condyn]

**Edited** So just to clarify, the whole entire exhaust duct (up until the tapered transition) is supposed to be 75% of the total window area? Before seeing this new drawing, I always thought the duct was supposed to taper down from port window face to the cylinder exit, and then taper back up into 1:1 at 2x bore from the window. Now it seems that the entire point of the initial flat floor, leading into the ski jump (with roof at 25 degrees) and later the convex floor at aux entry into the duct is to maintain the 75% all the way down. Pardon my ignorance of gas dynamics, but this makes more sense, as the main purpose of this special duct is thought to be because it keeps the fresh slug more dense via the smaller surface contact.

[wobbly]

Completely wrong end of the stick .
Nowhere ever , is it mentioned that the duct at any point is @ 75% CSA except at the exit face of the cylinder.
The floor is a convex ski jump with the main ducts CSA area reduced down from 100% at the port face, to be a minimum at the Aux duct intersection point , then the combined Main / Aux area is gradually reduced down
toward the exit such that it ends at 75%.

And who said that the intrinsic idea was to reduce the duct surface contact area of the retained return slug of overscavenged A/F mixture - not me.
Thats an assumption , and they are usually errors waiting to be revealed.
I have stated dozens of times the whole concept was based on achieving 0.8 Mach at the duct exit point , then have a highly tapered transition out to the 100% CSA header entry point.
This highly tapered divergent section of course reflects a changed sign wave ( negative ) very early back to the port , increasing scavenging whilst the piston controlled port is still open.
Just another piece of the puzzle.

But the lengths shown in all cases I have seen , are longer than the norm - giving more surface area , not less.
And of course , I have done the dyno experiment ( as proof of concept ) by lengthening the cylinder duct using a spacer with slots to allow water to cool right out to the spigot face , and the 1.5 X bore
( based on square engines ) makes more power , combined with a modified pipe to keep the Lt the same.
And EngMod agrees - funny that.

[Condyn]

Thank you for setting me straight. I misinterpreted something I had read.

[F5 Dave]

I don't want to derail this conversation as certainly back in the day I ruined my good 50 cylinder by making a nice taper exhaust port before I had any clue of this.


But to hark back to the 250MX long stroke advantage just for a segway. I've got back into Trials. And bothered to read the spec of my new bike. Which is industry standard.

250cc.
Bore 72.5. Stroke 60mm! So the other way around, and these are not high revving (or high power) engines.

The 280s and 300s keep the same stroke. Ok these are low BMEP engines with hardly a conventional pipe, but it seems odd that they would be so short stroked. We Dynod a Beta 250 20 years ago and it puffed out about 13hp. But was dynamite to ride at least for a beginner.