ESE's works engine tuner

[lohring]

Mark Atkinson's piston design gets around this issue.

Lohring Miller

[Haufen]

I got my simple plugs laser welded which were CNC maschined with a radius matching the piston shape (incl. it's piston offset... ),
the welding costs only 20 €...

Attachment 341651Attachment 341652

I like that, there is not much of a difference when comparing with a genuine RSA / APF Pin (other than the price - the pin is in the same region as the piston afaik)



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By the way, I want to part with my APF 2011 cylinder set (cylinder, head, piston, exhaust valve etc), any suggestions where stuff like this is best traded?

[polcat88]

The plugs work by blocking the connection that would otherwise exist from the aux.exhaust ports via the gudgeon pin bore in the piston to the A-transfer ports.
A spherical plug is not the optimum solution from a blocking point of view, but it was the optimum that I could produce with the machinery at hand. Producing plugs with rotation-preventing protrusions would have required CNC tools. And the leakage past a spherical plug is limited. Below is the worst case, with a leak path 9 mm wide and 0,47 mm deep: a reduction of 88% compared to a plug-less situation.
Attachment 341648

Below: the latest, spherical-capped, hideously expensive but moderately sealing Pankl pistonpin as used in the works Aprilias and my re-usable (save the environment) Torlon plug, the chamfered pin bore in the piston not being a good idea in either case.
Attachment 341649Attachment 341650

Frits, or Wobbly do you recall which grade of Torlon was used?

[wobbly]

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.

[husaberg]

[lohring]

That's a piston with very different design from an engine with a lot higher cylinder pressure. How many thousand hours was that engine run? The standards are a lot tougher than on a two stroke race engine runs less than 100 hours between overhauls. We'll see how a two piece piston works in a small two stroke. One problem is testing two ideas at once. It may be hard to decide if the piston or the new ring style is the problem.

Lohring Miller

[wobbly]

The piston plug idea is already well documented , the ring trapping idea has also been well tested - and then a patent applied for based on the result.
So both are a known entity, combining them will show all the advantages of no port linking plus the huge tuning leeway gained from removing
the limiting factor of running up against insufficient Blowdown STA.

[flyincat]

Wob, Frits, others...thanks for the pin plug refresher info! For the life of me I can't find a discussion I remember reading about port linking (short circuiting) affecting certain RPM's more than others. Are there certain RPM's that you can get away with port linking (no pin plug)? My thinking is for CVT application, where low and mid range only need enough power to get to the powerband RPM range without falling on it's face.

Would direct injection, or even boost port injection, negate the need for pin plugs?

[wobbly]

From my testing there is almost a linear effect of powerloss from port linking.
In the 125 I was testing the plugs gave around 2 Hp at 10,000 ( lowest used rpm ) and around 1 Hp at 13500 and above.
I imagine that this is a function simply of time/area of the " leak " decreasing as the rpm increases.
The only way changing the intake method would be effective against this issue is direct cylinder injection, you would think ,but even then you still
have exhaust gas pressure trying to get down the transfer ports.

[peewee]

i was thinking same. any negative affects of linking would decrease as revs go up simply because the time it has to link decreases

[190mech]

Some of the Vespa tuners claim their 'special' cylinders use flat sided pistons to promote linking to increase crankcase pressure!I always tell them to read the ESE thread,but they never do...

[ken seeber]

Years gone by in the era of 100cc air cooled rotary valve, reed valve and piston port inlet kart engines, guys used to shorten the piston skirt on the exhaust side such that, at TDC, the crankcase was open to the exhaust, by a couple of mm. Never saw any dyno figures etc, but some felt it was gainful.

[jamathi]

Years gone by in the era of 100cc air cooled rotary valve, reed valve and piston port inlet kart engines, guys used to shorten the piston skirt on the exhaust side such that, at TDC, the crankcase was open to the exhaust, by a couple of mm. Never saw any dyno figures etc, but some felt it was gainful.

Of course I also tried this , it made surprisingly little difference, but there was certainly no power gain!

[Frits Overmars]

Years gone by in the era of 100cc air cooled rotary valve, reed valve and piston port inlet kart engines, guys used to shorten the piston skirt on the exhaust side such that, at TDC, the crankcase was open to the exhaust, by a couple of mm. Never saw any dyno figures etc, but some felt it was gainful.

Yamaha even employed this scheme in a production machine; I think it was the RD400, but it was discontinued in their later models.

[katinas]

Yamaha even employed this scheme in a production machine; I think it was the RD400, but it was discontinued in their later models.

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.