ESE's works engine tuner

[mr bucketracer]

Pistons:

We had cast and forged pistons.
Cast pistons gave slightly more HP, but sometimes cracked.
0,8mm piston rings gave more HP than 1mm rings.
As the auxiliaries and transfers overlapped each other a certain power los was caused by this.
So closing the pin hole in the piston was tried.
There were many solutions that were tested, but they all caused some trouble.
In the end the best, and most reliable, solution was welding then closed.
This was very well done by PANKL in Austria, and never caused any trouble!

thanks for your imfo

[diesel62]

Do you mind me asking why do you think cast pistons made more hp than forged?

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[jamathi]

Because forged pistons had a tendency to 'bend' their dome inwards.

[diesel62]

Wow thanks for that.

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[jamathi]

When modifying a cylinder measuring duct sizes is not easy, especially in the curves!
You can see our solution to this problem on the photo....
Round 'sensors' fitted to a piece of welding rod!
We had them from 7-7,25- 7,5 and so on until 28mm.
Behind the cylinder, in the wooden block.

[Flettner]

Vannik or anyone that knows stuff, I don't have your software so don't know this, if combustion does not happen, what happens to the air velocity in the combustion chamber at / after TDC? Does the rapid turbulence in the combustion chamber stop and reverse at some stage, as the squish starts to open up again? Or does it keep going but just slow down a bit?

Jan, thank you, this is gold.

[guyhockley]

I think you are referring to the JBB 250 cc.
http://www.50c.nl/Archief%20Ton%20Ko...JBB/index.html

No, I'm not. I'm familiar with the JBB 250. When it was discussed, earlier, it was me that pointed out it uses the same sealing system as many outboards.
Frits posted a picture of a labyrinth seal made up of various diameter washers.

[husaberg]

No, I'm not. I'm familiar with the JBB 250. When it was discussed, earlier, it was me that pointed out it uses the same sealing system as many outboards.
Frits posted a picture of a labyrinth seal made up of various diameter washers.

He did indeed

You can easily build you own labyrinth with a stack of shims. Jan Thiel used this system in the Garelli 250cc V-twin. The whole shim package was only 5 mm thick.
Attachment 322755Attachment 322756

[Niels Abildgaard]

Because forged pistons had a tendency to 'bend' their dome inwards.

I do not understand .If the dome bends inward compression ratio go down and that is less power?

[jamathi]

Detonation.

This started te be a problem when 50cc engines started giving more than 17HP, around 1975.
At the time I thought this was a limit on engine power.
Nikasil plated cylinders were very prone to detonation.
Because of the rounded off edge at the top.
At Minarelli/Garelli I solved this problem by sticking the cylinder head insert 3mm into the cylinder.
A good solution, used for many years.
But at Aprilia we found an even better solution: plate the first 5 mm around the bore at
the top of the cylinder.
Later this was machined to a very sharp corner, and this eliminated completely the unnecessary
'dead room' at the top of the cylinder, it also gave 0,3HP more.....
A little bit of still remaining detonation was eliminated by modifying the inner wall of the
transfer ducts, cooling the piston.
But part-throttle detonation remained a problem.....
Which we never had on the dyno!
On the photo you see a piston after a 54HP run...
As long as you keep the throttle wide open a 2 stroke doesn't brake down!

[jamathi]

I do not understand .If the dome bends inward compression ratio go down and that is less power?

Yes...I think so.

[jamathi]

He did indeed

The shim package of the 250 Garelli was about 1mm.

[Vannik]

Vannik or anyone that knows stuff, I don't have your software so don't know this, if combustion does not happen, what happens to the air velocity in the combustion chamber at / after TDC? Does the rapid turbulence in the combustion chamber stop and reverse at some stage, as the squish starts to open up again? Or does it keep going but just slow down a bit?

The turbulence is caused by the breakdown of the main flow. Because of the viscosity (in effect the internal friction of the fluid) the main flow progressively break down into ever smaller eddies and if left long enough all the main flow and all the eddies will stop. The main flow is from the transfer port loop and a stronger better directed flow with more kinetic energy can generate a lot of turbulence before it stops. If you have weak flow by the time combustion happens you need the extra flow from the squish to generate extra turbulence to get good combustion. On the other side if you have strong flow and thus good turbulence the extra turbulence can speed up the combustion too much and you loose power but mostly overrev. This explains why engines do not always behave the same to squish changes. Good engines use squish to minimize end gas to stop detonation while poor engines use squish to add turbulence.

So to answer the question: Turbulence cannot reverse, it is a one way street after creation. The bulk flow with the squish opening will loop slower and slower, both because of the increase in volume and because it keeps generating turbulence until it completely stops.

[Haufen]

Thanks for the insight, Jan!

do you remember the difference between both of the A-port variations from the picture? Which was better, version A or version B?


And did you ever have the pin come loose on the pistons? I guess not, buit it does look brave to me.

[guyhockley]

The shim package of the 250 Garelli was about 1mm.

Very impressive! Thank you (both of you). You can tell we're all interested, Husaberg hasn't posted any boob pictures for ages...)