ESE's works engine tuner

[adegnes]

I have a tendency to jump in.
But if my port walls end just shy of the bore in a sharp point to get that tiny last bit of area, shouldn't that retain the same directional control?
The A/B walls "traditionally" converge a bit into the bore, now they converge a tiny bit before it.

Are these "dead spots"(green) necessary, or just a product of the need for bridges of a certain thickness for a traditional ring to survive?



My idea would be like re-sleeving a cylinder to a slightly smaller bore, keep the same port angles but let them end in a sharp edge just outside the bore.

[Frits Overmars]

Are these "dead spots"(green) necessary, or just a product of the need for bridges of a certain thickness for a traditional ring to survive?

Neither. You do need bridges there, but they need not be wider than about 4° each (see the difference between trailing and leading position angles below right) or about 4% of the bore.


I would not use a sleeve if I were you, Alex; it would seriously hamper heat transfer.

[_____]

We set port timing by the edge of the piston crown. Yet the ring is roughly 2mm down and is the real seal surface. Is our port timing off? I ask because if I made a regular dykes style ring that seals at the crown tangent point is the timing going to change? Does this matter? Anyone test this?

I once checked that with an 1D/0D simulation programm, by adding a very small "nose" upon the exhaustport.
The nose is increasing the exhaustport height with the height of the ringland, the width is the circle-ring area of the ringland. The difference was quasi non existent, since the cross-section of this "port" is way to small for serious mass flow.
Comparable to a foulstroke where the valve opening perioud is only interesting after 1.0mm of valve lift.

On the "reversed" Dykes ring: The ring land on a few pistons of mine looked pissed as well, whilst dealing with a big exhaust port.
@wob, which dimension of pistons were tested with the 100% exhaust-width? D54mm? How long used?

Cheers, Chris

[adegnes]

Neither. You do need bridges there, but they need not be wider than about 4° each (see the difference between trailing and leading position angles below right) or about 4% of the bore.


I would not use a sleeve if I were you, Alex; it would seriously hamper heat transfer.

Yes, that drawing was of the original iame M50 cylinder, lot's of dead space.

But if the ring didn't care, wouldn't 0° be even better?



Worry not, people have offered to coat the cylinders for me, no liner.

I really want to do everything but the coating "in house", a long way there both equipment- and knowledge wise.

[SwePatrick]

Due to piston is tapered it can rock in the bore.
This makes it very hard for the ring to seal if you restricts it´s movement.
And piston is rocking the most in bdc and often is the ring hooking into the exhausts 'floor'

There are no free lunch here, sadly enough.

[Frits Overmars]

... if the ring didn't care, wouldn't 0° be even better?

Even if the ring doesn't care (I have my doubts), the piston will; it will act according to Murphy's Law: if it can topple into a port, it will. You'd need quite a long piston. Or instead of combining Mark Atkinson's piston with Denver Lawson's inside-out L-ring, you could go the whole way and copy Flettner's epicyclic crank-rod system. That has a much better guidance plus a handful of other advantages.

[adegnes]

Due to piston is tapered it can rock in the bore.
This makes it very hard for the ring to seal if you restricts it´s movement.
And piston is rocking the most in bdc and often is the ring hooking into the exhausts 'floor'

There are no free lunch here, sadly enough.

Even if the ring doesn't care (I have my doubts), the piston will; it will act according to Murphy's Law: if it can topple into a port, it will. You'd need quite a long piston. Or instead of combining Mark Atkinson's piston with Denver Lawson's inside-out L-ring, you could go the whole way and copy Flettner's epicyclic crank-rod system. That has a much better guidance plus a handful of other advantages.

But I want my free lunch!
If I only delete the B/C bridges, and run the cylinder 90° twisted to have most of the thrust load where there's actually some wall left?
I'll go back and read up on Fletners crank(and the ring in bore idea)

[Muhr]

Since I am pondering piston rings and placement on the piston I have this thought that I don't think we have talked about.


Or maybe I just have forgotten.


We set port timing by the edge of the piston crown. Yet the ring is roughly 2mm down and is the real seal surface. Is our port timing off? I ask because if I made a regular dykes style ring that seals at the crown tangent point is the timing going to change? Does this matter? Anyone test this?

I put 170psi on a 4mm2 and 2mm high cube which of course is very much better boundary layer condition.
around 600ms so about 0.123cc at 13000 rpm on a 125cc but probably much much lower

[SwePatrick]

But I want my free lunch!
If I only delete the B/C bridges, and run the cylinder 90° twisted to have most of the thrust load where there's actually some wall left?
I'll go back and read up on Fletners crank(and the ring in bore idea)

You need the bridges to control the direction of the incoming gasses, if you blend them together before entering the bore you need to start develop the shape again to get the correct direction for effictivly scavenge the bore.
I can be brave and say it´s equally important in the exhaust also.

Don´t underestimate existing solutions, they have been developed for many many years to have reached the shape they´ve got today.

[wobbly]

There is no dead area in front of the boost port.The hook ( radius ) twists the inflowing gas column axially underneath the boost port.
Its real easy to see for yourself, turn a cylinder upside down that has the B port hook , and use a stream of water dropping down into the duct from a tap.
You will see immediately the effect , hard to explain , harder to understand how it happens.
Many of the latest high performance cylinders have the rear wall of the B port closest to the boost port, crossing the centerline about 1/3 length away from the bore to the mid point.
So this is a much steeper exit angle than around 1/2 way to the bore center as was used previously.

I believe SwePatrick is correct - as I said before the gas columns entering the cylinder must remain coherent - all the way up to the point they become the single leaning tower scavenging loop..
This coherent column flow is even badly affected by the smallest chamfer on the transfer ports at the bore , creating eddies around the columns sides that then detach and become mixed with exhaust residuals.
So if a tiny chamfer fucks the scavenging efficiency imagine what will happen to two individual flow streams colliding " outside " the bore.

[adegnes]

You need the bridges to control the direction of the incoming gasses, if you blend them together before entering the bore you need to start develop the shape again to get the correct direction for effictivly scavenge the bore.
I can be brave and say it´s equally important in the exhaust also.

Don´t underestimate existing solutions, they have been developed for many many years to have reached the shape they´ve got today.

I totally get that point, I don't want to blend them before the bore though.
Look at it this way, I'm not going to remove the bridges, but make them 0.01mm wide. Same angles as before, just that tiny bit more area.

You're of course right about existing solutions, but it's not where the fun is for me.

[TZ350]

.
Been getting my engine back together again after replacing the rod kit and using a special crank pin Flettner made for me that has direct posi lube oiling to the big end.

The current problem I am having is trying to get three variables to align up. Squish, Compression Ratio and Port Timing.

Getting everything correct by hand is so fiddly and time consuming I admit frustration and a less than satisfying result. Next time I am going to pay someone with a CNC machine to make the inserts for me.

[adegnes]

There is no dead area in front of the boost port.The hook ( radius ) twists the inflowing gas column axially underneath the boost port.
Its real easy to see for yourself, turn a cylinder upside down that has the B port hook , and use a stream of water dropping down into the duct from a tap.
You will see immediately the effect , hard to explain , harder to understand how it happens.
Many of the latest high performance cylinders have the rear wall of the B port closest to the boost port, crossing the centerline about 1/3 length away from the bore to the mid point.
So this is a much steeper exit angle than around 1/2 way to the bore center as was used previously.

I believe SwePatrick is correct - as I said before the gas columns entering the cylinder must remain coherent - all the way up to the point they become the single leaning tower scavenging loop..
This coherent column flow is even badly affected by the smallest chamfer on the transfer ports at the bore , creating eddies around the columns sides that then detach and become mixed with exhaust residuals.
So if a tiny chamfer fucks the scavenging efficiency imagine what will happen to two individual flow streams colliding " outside " the bore.

Thank you both for the input!
Interesting about the steeper angles, so in effect they have less "hook"?
Dead space was the wrong word, what I ment was "potential port area not in use". Do you think it's important the columns collide a certain distance from the bore, could sacrificing port area for collision closer to center be beneficial?
If not maybe my razor sharp walls could work?

[jonny quest]

Adegnes, what is the most effective thing on making power in a 2 stroke cylinder? (I said cylinder, don't come at me with pipe)

Focus on that. You can then always grind your transfers one step at a time during testing to verify that getting rid of transfer bridges will lose HP. I'd be more inclined to believe taller transfers may make more power with a superior exhaust port.

[adegnes]

Adegnes, what is the most effective thing on making power in a 2 stroke cylinder? (I said cylinder, don't come at me with pipe)

Focus on that. You can then always grind your transfers one step at a time during testing to verify that getting rid of transfer bridges will lose HP. I'd be more inclined to believe taller transfers may make more power with a superior exhaust port.

Nitromethane/hydrazine mix? 😁

Yeah, sounds like a plan.
If only someone could hand me a bag of money, I could take a year off, buy the necessary equipment, and start chewing through cylinders with ridiculous ideas.