ESE's works engine tuner

[Vannik]

Jan Thiel wrote that he has never understood why people try to make pistons lighter. With a heavier piston he could do many test runs without losing power, he said. I believe every word he says.

My understanding of Jan's comment is based on the fact that Aprilia made pistons so light that after a couple of runs the dome started to sag and compression and power was lost. So it was not the mass of the piston Jan was addressing but its mechanical strength at in-cylinder temperatures and the fact they made them too light. If I misunderstood Jan please tell me.

[Frits Overmars]

Hello Frits, I don't know if your quote was intended for me, but I do feel it applies to me. I am an amateur, a modest novice who realizes that he still has to learn everything that others have already forgotten.
There is the Master of 2stroke, Frits, Neels, Wobbly,... and others. All people with an amount of knowledge and experience that could fill an entire galaxy. I have deep respect for you and them.
I still have to learn how to roll a cigarette that looks like an expansion pipe. They and you have made countless of them. It almost makes me scared in these first posts to ask about something that could be ridiculous.

Hi Jan, don't you worry about ridiculous questions. Every day I encounter a level of ridiculousness that you couldn't equal if you tried. Yes, I am referring to Fakebook.
That 'combination lock' tile was intended to confirm a comment made by Wobbly, but I think it's applicable for all of us.
Rolling a cigarette that looks like an expansion pipe? I used to be proud of rolling them into a nice cylindrical shape while driving, with one hand, on my knee. But that was 50 years ago when everyone and their mother smoked. Speaking of smoking: when I was still commuting back and forth between the Netherlands and Italy, I always had to bring tobacco and sigarette paper for Jan Thiel because it was hard to find over there.
Jans philosophy about smoking: "I read that if you start smoking at the age of 17, your life expectancy is that you will live to be 57. I started smoking at the age of 37, so I will live to be 77 and I'll never make that without smoking!" (Jan hasn't smoked for years and he is now 83).

I read forums, Frits's columns and all his tips and tricks, I try to use/understand a little bit of Engmod2t, I read Jan's masterpiece book in one go. 2 examples:
Jan Thiel wrote that he has never understood why people try to make pistons lighter. With a heavier piston he could do many test runs without losing power, he said. I believe every word he says.
Frits advises and motivates to round off the piston edge instead of the transfers. Better piston head cooling and flow and behaves like a delaval nozzle on the exhaust side. I would therefore like to provide my piston with such a rounding. Do I also have to make the same rounding in the combustion chamber? If not, am I not creating a detonation in that "lost space" if this zone does not also have a rounding? Is this only recommended for racing? And do you just stay away from it for street use?

If you radius the piston timing edge, you need to make the same radius at the outer diameter of the squish band in the head, otherwise you'd create a detopnation zone.
And it's generally applicable, not just for racing (I radiused the piston of my moped in 1963 because I had no way of raising the transfer ports without ruining their shape).

My understanding of Jan's comment is based on the fact that Aprilia made pistons so light that after a couple of runs the dome started to sag and compression and power was lost. So it was not the mass of the piston Jan was addressing but its mechanical strength at in-cylinder temperatures and the fact they made them too light. If I misunderstood Jan please tell me.

Jan was well accustomed to sagging piston domes. The pistons in his 125cc Garelli engines self-adjusted to their working conditions that way and the engines ran fine with them, gaining six straight world titles. But the Aprilia was from a different level. The unbeatable Garelli 125 twins produced 46 HP; the Aprilia 125 single produced 54 HP, so the thermal load in the single was a lot higher.

​

[Jan Van Hamme]

Hi Jan, don't you worry about ridiculous questions. Every day I encounter a level of ridiculousness that you couldn't equal if you tried. Yes, I am referring to Fakebook.
That 'combination lock' tile was intended to confirm a comment made by Wobbly, but I think it's applicable for all of us.
Rolling a cigarette that looks like an expansion pipe? I used to be proud of rolling them into a nice cylindrical shape while driving, with one hand, on my knee. But that was 50 years ago when everyone and their mother smoked. Speaking of smoking: when I was still commuting back and forth between the Netherlands and Italy, I always had to bring tobacco and sigarette paper for Jan Thiel because it was hard to find over there.
Jans philosophy about smoking: "I read that if you start smoking at the age of 17, your life expectancy is that you will live to be 57. I started smoking at the age of 37, so I will live to be 77 and I'll never make that without smoking!" (Jan hasn't smoked for years and he is now 83).
If you radius the piston timing edge, you need to make the same radius at the outer diameter of the squish band in the head, otherwise you'd create a detopnation zone.
And it's generally applicable, not just for racing (I radiused the piston of my moped in 1963 because I had no way of raising the transfer ports without ruining their shape).

Jan was well accustomed to sagging piston domes. The pistons in his 125cc Garelli engines self-adjusted to their working conditions that way and the engines ran fine with them, gaining six straight world titles. But the Aprilia was from a different level. The unbeatable Garelli 125 twins produced 46 HP; the Aprilia 125 single produced 54 HP, so the thermal load in the single was a lot higher.

​

Thank you very much for the words of wisdom.
In 1963... I was -7 years old. (Born december 1970)

Without the radius of the piston timing edge I would normally have to make my transfer port 12mm high to get the desired timing (129.4°).
The radius increases the timing.
To achieve the same 129.4° I can only go 11.11mm high. This reduces the transfer window area.
Does this not have a negative effect on the power? Or does the flow improvement due to the radius fully compensate for this transfer area reduction?

[Frits Overmars]

Without the radius of the piston timing edge I would normally have to make my transfer port 12mm high to get the desired timing (129.4°). The radius increases the timing. To achieve the same 129.4° I can only go 11.11mm high. This reduces the transfer window area.
Does this not have a negative effect on the power? Or does the flow improvement due to the radius fully compensate for this transfer area reduction?

A radiused piston timing edge, and a radiused top edge on the exhaust port, give a more gradual initial port opening. If we want the effective timing to remain the same, we can make the geometrical timing (when you see the first glimpse of light through the port) a few degrees higher. The mathematical difference is not so easy to explain but the best practical approach is to measure the port timings with a 0,7 mm feeler gauge bent at 45° and assume that radiused and non-radiused piston and port edges should give the same piston position when measuring.

[wobbly]

If you draw the radius piston concept out in CAD you will see that using the dead stop method ( standardized now as a 0.7mm blade that gives an easy calculation of 1mm of port height difference )
the cylinder will need to be dropped 0.6X the radius on the piston to get the same port height/timing.
Thus for a 1mm radius the cylinder needs to be dropped 0.6mm.
At BDC we will now have effectively 0.6mm of radiused piston timing edge sitting above the duct floor.
As testing would indicate , if this is done power increases , so maybe the reduced effective port area has a downside , but this is swamped by the flow increase factor.

As my testing has discovered , the boost port flow regime is a bigger issue.
What I believe happens is that as the boost port is severely angled upward the flow going over the radius attaches to the piston and is pulled downward - directly increasing short circuiting
by changing the leaning tower angle away from the rear wall.

One solution is to cut the piston radius using a dividing head , and stopping the radius cutter just short each side of the boost port.
But this changes the boost port timing , as now the cylinder has been dropped to suit all the other ports.
Another solution is to lift the boost port floor upward well above BDC , so the flow column doesnt have a chance of attaching during the bulk flow period around BDC.

I have not had a chance to actually try either of these options in a back to back test.
The result of simply radiusing the piston and dropping the cylinder is a good increase in power up the front side , but overev directly after peak is diminished alot more - maybe not an issue for many
but NFG for a KZ.

[skako]

My suggestion on how to measure the effective height of the port, for any piston position.
Prof. Jante tested the roundness of the piston edge on a 2-stroke diesel engine type NZD 12.5.
Jante determined that the optimal radius of rounding of the edge of the piston is about 5.5% of the cylinder diameter.
This should be taken into account when looking at the drawing.
The dimensions in the drawing are only for better understanding.

[Jan Van Hamme]

My suggestion on how to measure the effective height of the port, for any piston position.
Prof. Jante tested the roundness of the piston edge on a 2-stroke diesel engine type NZD 12.5.
Jante determined that the optimal radius of rounding of the edge of the piston is about 5.5% of the cylinder diameter.
This should be taken into account when looking at the drawing.
The dimensions in the drawing are only for better understanding.

I had seen in Frits' tips and concepts that the radius had to be 5% of the stroke. That's how I drew it too.
A combination lock of 10?
...I think my novice radius timing question here is going into Pandora's open box. Where we have to decipher the Davinci code using a cracked enigma machine!

In Engmod2T my RD125LC from 1982 (199°/129,4°/YZ125reedvalve) with a non radius timing edge reaches 34.5HP at 11000rpm.
I think I would do well to try to put that into practice first.
Through a reinforced coupling and a self-balanced and aligned crankshaft with silver-plated bearings and a solid lightened VHM 110mm conrod, maybe with ceramic main bearings, an Italkit PI.01.58A.V2 piston where i make the windows in the same shape as the inlet port,I hope to be able to transfer 31 HP to the ground without breakage.
If that works, I will be extremely satisfied.

[husaberg]

In 1963... I was -7 years old. (Born december 1970)

An accountant....

[Jan Van Hamme]

An accountant....

No, not an accountant.
I have a bachelor's degree in mechanical design and production technology.
That's nothing compared to an accountant.
Late at night, slumped in the sofa after about 3 "Rochefort 10" beers, I can no longer count whether there were 3 or 4.

[Frits Overmars]

My suggestion on how to measure the effective height of the port, for any piston position.
Prof. Jante tested the roundness of the piston edge on a 2-stroke diesel engine type NZD 12.5.
Jante determined that the optimal radius of rounding of the edge of the piston is about 5.5% of the cylinder diameter.
This should be taken into account when looking at the drawing. The dimensions in the drawing are only for better understanding.

Excellent, Skako. So you have Jante's books too? For those who are curious now: "Über Verbrennungsmotoren und Kraftfahrwesen, Band 2" by professor Alfred Jante.
It won't be easy to find those books now, but if you manage to do so, please let me know; there is still a volume missing in my library.

The research on of the exhaust top edge radius, page 333 and subsequent, shows that Jantes NZD 12.5 research engine had a bore of 90 mm and a stroke of 125 mm.
My research into the effects of the bore/stroke ratio led me to make the radius dependent not on the bore, but on the stroke, and I found an optimum at 5% of the stroke.

[Frits Overmars]

If both the piston and the exhaust port have a timing radius, and if both radiuses are not tangential to the bore, and if the top of the exhaust port has an elliptical shape, then calculating the open port passage degree by degree for the purpose of determining the angle.area becomes quite a job. Thank god for computers.

[Jan Van Hamme]

Excellent, Skako. So you have Jante's books too? For those who are curious now: "Über Verbrennungsmotoren und Kraftfahrwesen, Band 2" by professor Alfred Jante.
It won't be easy to find those books now, but if you manage to do so, please let me know; there is still a volume missing in my library.

Frits, I found this one.

[skako]

Excellent, Skako. So you have Jante's books too? .....

Yes Frits, I have that book on my desk. I saw her for the first time in 1985. I was looking for her for many years. I managed to get it 8 years ago.
Guys, forgive me for my (creative) mess. I know it's not a virtue. I am interested in everything and bring everything to the table. But it is my work corner where I enjoy it in my own way. Only my wife resents me very much for that.
But which man is perfect in life?

[Frits Overmars]

Frits, I found this one.

Thank you very much Jan. I've got Band 2 here but am still looking for Band 1. I will contact them and see what they've got.

[Frits Overmars]

Yes Frits, I have that book on my desk. I saw her for the first time in 1985. I was looking for her for many years. I managed to get it 8 years ago.

Your book is in better shape than mine, Skako. You wouldn't happen to have two copies of Band 1, would you?