ESE's works engine tuner

[peewee]

Tried this on Honda NS 250, at TDC exhaust connect with crankcase through cut 10x10mm on piston EX side skirt. Surprisingly at low and mid rpm nothing changes, but from 9000 to 13000 rpm power much softer.
Yamaha do the same on latest 2018 YZ 250, just open not main EX, but satellites when piston is at TDC ( add pic).
Maybe on RD400 and YZ 250 they tried to do more friendly engine character, but maybe not.

about 25yr ago ktm did that same thing on a dirtbike engine. im not sure if it was intentional or just a byproduct of using such a high wristpin

[F5 Dave]

Funny. Mike tried that when he sleeved down a RGV barrel and it was a bit rubbish, as piston too thin to cover bridged port. Everything better with a wider skirt piston.

[peewee]

I used 4203 rod.
Mark is taking the screw top piston one step further after I wised him up to a patented reverse L ring design that traps the
vertical leg and prevents bulging into large unbridged ports.
Our man on Two Stroke Stuffing is on the same path.

how much power could the rsa have if jan had a chance to try nonbulging rings ?

[wobbly]

60 Hp easy if simply removing the bridges on the 3 port.
But the transfers would need to be raised - as they are perfectly matched to the existing effective Blowdown STA.

[Flettner]

Raised? How much?
I've got a cylinder with a static ring, pinned.

Haven't tried it yet, intetesting to see how well this pinned piston ring works, are there any real world results yet?

[katinas]

Tested Suzuki RGV 250 1/2 engine with lower crankcase separator and flow directly to transfers, like tested on Honda NS.
Engine reaction from 0 to 8000 rpm very similar to NS ( clean burning at lower revs).
But from 8000 rpm, when power valve opens, engine stopped and only first gear overcome 8000-10000 rpm dip.
From 10000 to 12500 rpm nothing special from std.
Then made two 16 mm holes on separator sides to add pressure from crankcase and this immediately eliminate dip.
In normal mode, without separator, engine lost cleanliness at lover revs, but at higher goes better than with std piston.
So needed more tests, but as on NS engine work in a good way from first run , on RGV all things more complicated.
Would be interesting to try new separator with reed valves.

[katinas]

about 25yr ago ktm did that same thing on a dirtbike engine. im not sure if it was intentional or just a byproduct of using such a high wristpin

Maybe on Yamaha YZ 250, gains from higher cuts, overcome looses from opened EX satellites.
And very strange that piston intake side skirt legs is higher than B transfers windows lower edges, when piston is at TDC. This open B windows little more, but piston legs working in danger zone.
Patent EX communicating with A through piston https://patents.google.com/patent/US...shihisa+Nemoto

Testing on Dyno, shows that rising side cuts as much as possible (without short cut with satellites) on std piston with KTM SX 65/85/125 add little hp. Last week on the new Husqvarna TC 65, just with modified std piston, power rise up 0,8 hp with the same mid (higher cuts 0,3 hp. rounded piston with sharp edge at C 0,5 hp.)
Its funny, some time ago, when we rising side cuts we thinking that it helps better flow from crankcase when piston is at BTC. Now we doing the same, but thinking that it add longer suction pulses to transfers ports when piston is at TDC. But this works on reed engine, on rotary opposite, as on Jan's engines cuts is much lower and did not open trans windows at all when piston is at TDC .

Add RGV Di piston at TDC

[wobbly]

Without doing a full sim analysis on the RSA 125 ( again ) with the new Exhaust width I have no idea what will be needed to
get the Blowdown and Transfer STA back into sync Neil.
The setup that Mark and Mr Stuffing are working on isnt " pinned " as such.
It is a reversed L Dykes ring , such that the vertical leg is trapped within the ring groove.
Its under a patent issued to Savice, the engine design consultancy company i worked for in China.

[Flettner]

thats a bit rich, China useing the patenting system.😆

[DoldGuy]

thats a bit rich, China useing the patenting system.😆

Now that’s funny!!!

[DoldGuy]

Tried this on Honda NS 250, at TDC exhaust connect with crankcase through cut 10x10mm on piston EX side skirt. Surprisingly at low and mid rpm nothing changes, but from 9000 to 13000 rpm power much softer.
Yamaha do the same on latest 2018 YZ 250, just open not main EX, but satellites when piston is at TDC ( add pic).
Maybe on RD400 and YZ 250 they tried to do more friendly engine character, but maybe not.

Katinas,
Do you know if the satellites/sub ports open on the 2017 and earlier? It appears the 2018 received a new/different cylinder. I have been working on a cylinder that has the satellites/subs open like the YZ and have searched for a solution/piston to cover the ports at TDC, but my concerns over this might not be warranted.

[katinas]

Katinas,
Do you know if the satellites/sub ports open on the 2017 and earlier? It appears the 2018 received a new/different cylinder. I have been working on a cylinder that has the satellites/subs open like the YZ and have searched for a solution/piston to cover the ports at TDC, but my concerns over this might not be warranted.

Hi,
When Yamaha changed YZ 250 engine in 1999 ( piston from 68 to 66,4 mm ) looks like satellites was opened until now. We really surprised to see this, when changed the piston on the 2018 YZ 250 two moth ago.
Before 1999, with 68x68 mm engine, they use piston with extensions to cover satellites.

[Frits Overmars]

All MotoGP-races live on the internet: https://www.servus.com/tv/jetzt-live/ (German-spoken; Servus is a TV-station owned by Red Bull).

[peewee]

Hi,
When Yamaha changed YZ 250 engine in 1999 ( piston from 68 to 66,4 mm ) looks like satellites was opened until now. We really surprised to see this, when changed the piston on the 2018 YZ 250 two moth ago.
Before 1999, with 68x68 mm engine, they use piston with extensions to cover satellites.

you can probly just use the 250sx piston. that should cover the sub ports

[ken seeber]

BATTLE OF THE BULGE

Nope, not really, but the measured bulging of a ring with progressively increasing port chordal widths.
So, I made up a small mandrel and bored it to 54.0 and used a KZ standard style 1.0 * 2.20 Meteor piston ring. The mandrel was faced off on its underside and then grooved out so a vernier could measure the top of the ring between that and the flat. The pics tell the story really.

[
Then, with a fixed stop arrangement in the mill, the slot was progressively widened in 2 mm steps using an Ø8 mm cutter. Between each cut the ring height was measured, both externally with the verniers and, also using verniers, the inside diameter of the ring on an axis in line with the centre of the “port”.

To ensure consistency, the ring was always orientated in the same position and was pushed into place using a shouldered mandrel to place it into the centre of the port each time.
The zero bulge/reference point was set at the initial port width of 18 mm, based on the assumption that no bulging could ever be present at such a small chord width.
Results were the average of the internal and external measurements taken at each port width. If I was to do this again, I can think of better methods of measurement to eliminate the experimental variation that was present.

One can see the real action starts around the 70% port width.



What does all this mean? Not sure in that these are just a series of measurements in a static test rig. If the grand plan is to have the widest port possible consistent with the ring not snagging, then the practical limit ultimately would have to be tested on an engine. Major influencing factors would be:
• The shape of the roof of the port
• The radius of the port between the roof and the sidewalls.

Another factor is gas pressure. As is well known, the gas pressure in the cylinder activates the sealing of the ring by providing a pressure force on the effective projected area of the ring. At the point of EPO, the gas pressure in the cylinder might be up to 5 bar, and this would certainly be enough to assist the outward bulging of the ring. But at this point, it is no big deal as the ring is in fresh air (exhaust gas really) . Assuming the ring passing over the floor of the exhaust port is also not an issue due to well rounded shape, the real issue would be the rising situation when the ring could snag on the roof of the port.

So, dunno if anyone has progressively widened a port to the point of destruction, but most figures I have seen are around 70 – 72% maximum.
Clearly at widths of 80% plus, destruction looks likely. Hence the need for some form of containment at the 100% level as proposed by Wob, Mark & old mate in 2 stroke stuffing. To me this is going to take a serious tolerancing & mfg exercise to make it work, but I hope it does.

The alternative to achieving more exhaust area is to add more ports than the current generic 3 port arrangement. To do this will most likely require an alternative scavenging arrangement and we all know what some of these are.