ESE's works engine tuner

[diesel pig]

No, conventional bridge port except twin outlet but with more ports further round the cylinder where exhaust normally cant go. Extra eye ports but with a rotating valve that can open and shut as needed. Extra blowdown but thats all.

I still have the sleeve engine in a box waiting for a spare YZ250 gearbox to materialize.

That begs the question do you mean the exhaust eye ports open when the revs rise, like some Yamaha's and Kawasaki's or do you mean the ports that open and close each revolution? A system I remember reading about decade's ago. A lotus test engine using that system had a a mini crank like set up driving off the end of the main crank opening and closing the exhaust valve (the valve would completely close the port each time) each revolution? interesting none the less either one.

[wobbly]

So now we have a circular discussion, what Hp are the transfers capable of now , and if its easy to add a bunch of Blowdown , yes of course its easy to lift the
transfers. But when you do that , you loose Blowdown STA and thus the Hp capability.
We ( you ) need to generate hard numbers of where you are at - then extrapolate out to where you want to be using whatever new geometry has been concocted.
I am assuming , you are not looking to exceed the RSA ( crank ) bmep of 16.5 Bar @ 13000 , but even a much less powerful device needs to have the STA numbers in balance.

Edit - and I am struggling to understand why increasing Blowdown capability is " good " but the return stuffing action from the rear cone is " bad " so needs to be reduced.

[Flettner]

So now we have a circular discussion, what Hp are the transfers capable of now , and if its easy to add a bunch of Blowdown , yes of course its easy to lift the
transfers. But when you do that , you loose Blowdown STA and thus the Hp capability.
We ( you ) need to generate hard numbers of where you are at - then extrapolate out to where you want to be using whatever new geometry has been concocted.
I am assuming , you are not looking to exceed the RSA ( crank ) bmep of 16.5 Bar @ 13000 , but even a much less powerful device needs to have the STA numbers in balance.

Edit - and I am struggling to understand why increasing Blowdown capability is " good " but the return stuffing action from the rear cone is " bad " so needs to be reduced.

No, reverse pulse is not reduced, its redirected back up the main port like a normal engine. The extra eye ports are only there for blowdown after that they 'disappear', at TPO its back to normal twostroke until next cycle.

[TZ350]

Bit of dyno time with the 250 today. Main jet setup for Methanol only and the Pilot jet draws Petrol exclusively.

Started with 3L of Methanol and Petrol. Finished with 1L of Methanol and 2L of Petrol. Much heavier Petrol consumption than I would have thought.

[Grumph]

2 : 1 ratio is about right given the pilot jet is flowing continuously.

[Flettner]

So now we have a circular discussion, what Hp are the transfers capable of now , and if its easy to add a bunch of Blowdown , yes of course its easy to lift the
transfers. But when you do that , you loose Blowdown STA and thus the Hp capability.
We ( you ) need to generate hard numbers of where you are at - then extrapolate out to where you want to be using whatever new geometry has been concocted.
I am assuming , you are not looking to exceed the RSA ( crank ) bmep of 16.5 Bar @ 13000 , but even a much less powerful device needs to have the STA numbers in balance.

Edit - and I am struggling to understand why increasing Blowdown capability is " good " but the return stuffing action from the rear cone is " bad " so needs to be reduced.

So if you had extra blowdown area, you wouldnt use it?
It could be made to not come into play until you run out of normal blowdown (time) area.

[wobbly]

Yes of course but only if the transfer ports could keep up ie balanced transfer and blowdown STA

[Flettner]

Yes of course but only if the transfer ports could keep up ie balanced transfer and blowdown STA

So whats stopping the twostroke making more power, lack of ultimate blowdown or transfer ability?

Ulitimately

[wobbly]

Both are equally important , if you do an analysis of the RSA the power capability of the engines Transfer and Blowdown STA are perfectly matched , when the affect of
the Ex port timing edge radius on the Cd during Blowdown is taken into account.
There is no more room for transfer chordal width around the bore , and you cant lift them without reducing the Blowdown STA.
So that engine is maxed out , porting wise , and any further power increases have to come from using pipe and or Exhaust duct trickery.

[Flettner]

Both are equally important , if you do an analysis of the RSA the power capability of the engines Transfer and Blowdown STA are perfectly matched , when the affect of
the Ex port timing edge radius on the Cd during Blowdown is taken into account.
There is no more room for transfer chordal width around the bore , and you cant lift them without reducing the Blowdown STA.
So that engine is maxed out , porting wise , and any further power increases have to come from using pipe and or Exhaust duct trickery.

So you are saying, if you had more blowdown you could run the transfers higher, to get suitable STA numbers, keep everything in equilibrium.

Time / area / pressure. The next thing to work on is pressure, transfer pressure, I guess.

Im trying to workout whether I should go ahead with this new cylinder, with extra blowdown .... or am I wasting my time?

[Flettner]

That begs the question do you mean the exhaust eye ports open when the revs rise, like some Yamaha's and Kawasaki's or do you mean the ports that open and close each revolution? A system I remember reading about decade's ago. A lotus test engine using that system had a a mini crank like set up driving off the end of the main crank opening and closing the exhaust valve (the valve would completely close the port each time) each revolution? interesting none the less either one.

Opens and closes every cycle but only open for blowdown fase, shut the rest of the time. When shut it turns the main exhaust port into a normal bridged port setup. Although twin outlets at approx 30 degrees each from centre. Much like this but with straight ports not curved and the extra 'Valved' eye ports further round the cylinder. When transfer happens they are shut, ie no influence on the transfer regime.
Am I wasting my time? I was going to get stuck into the supercharged twin (fourstroke) but thats going to cost too much, at the moment. A new cylinder cast is much cheaper and probably less time to build. And fuck fourstrokes 😁

[Grumph]

Ideally you'd do it in a sim. But the speed you can do cylinders - and at what seems to be lowish cost - makes me think you'd have it running before the sim finished...

Play to your strengths.

[pete376403]

Opens and closes every cycle but only open for blowdown fase, shut the rest of the time. When shut it turns the main exhaust port into a normal bridged port setup. Although twin outlets at approx 30 degrees each from centre. Much like this but with straight ports not curved and the extra 'Valved' eye ports further round the cylinder. When transfer happens they are shut, ie no influence on the transfer regime.
Am I wasting my time? I was going to get stuck into the supercharged twin (fourstroke) but thats going to cost too much, at the moment. A new cylinder cast is much cheaper and probably less time to build. And fuck fourstrokes 😁

Build a uniflow - supercharger, ported cylinder for intakes and poppets in the head for exhaust. Best of all worlds

[Flettner]

Build a uniflow - supercharger, ported cylinder for intakes and poppets in the head for exhaust. Best of all worlds

We .... dont do popets. We do ports.

[Frits Overmars]

Build a uniflow - supercharger, ported cylinder for intakes and poppets in the head for exhaust. Best of all worlds

Uniflow: OK.
Supercharger: hmmm, not very efficient.
Ported cylinder for intakes: OK.
Poppets in the head for exhaust: no way.
A blowdown angle.area analysis will tell you why. Poppet valves rest on their seats. They do not move. When they must open, they start moving with an initial velocity of zero. The open area slowly increases and the cylinder pressure slowly drops, generating a mediocre exhaust pulse.
A piston port is opened by a piston that has reached its maximum velocity when it starts opening the port. The exhaust area opens with a bang and the exhaust pulse is far stronger than what a poppet valve could generate.
One more thing: poppet valves are heated from all sides by the passing exhaust gas. They dearly need the contact with the valve seats to get rid of that heat.
But in a two-stroke they are heated twice as often and their resting time between exhaust phases is halved.