[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)

el castor a écrit:

Jan Thiel a écrit:: Reducing wall thickness also proved to improve HP.
The limit is mechanical reliability.
Which makes me think that fixing the cylinder to the crankcase at its bottom is all wrong!
The combustion forces should not stress the cylinder!

Interesting. What would be your solution?
Instead of the bottom-screwed-cylinder four spacer bolts up to the cylinder head? (Of course wide enough to not disturb the coolant or the scavenge).

Yes, indeed!
Herbert Rittberger once had the best solution I think.
Take a look at his Krauser engines!
Also the solution used on the Morbidelli/MBA was good.
A combination of these 2 systems would be ideal!
For the bolts Dilavar would be the best material.
It has the same expansion rate as aluminium and was used for Porsche's headbolts!

Nombre de messages : 8 Localisation : AUSTRALIA Date d'inscription : 11/11/2012

Jan Thiel a écrit:

Forgi a écrit:

Frits Overmars a écrit:: Forget about the mean area of the exhaust port, Forgi. Look at the blowdown area.
What I wrote in the seventies, is 35 years old! And what I showed in the exhaust concept that I posted some time ago, is an extreme simplification, only meant to help beginning tuners on their way.

It is quiet interesting Frits! So are you telling me that the exhaust port's time area doesn't mind? :-) Only the blowdown what is important? Well I always intend to make the whole exhaust port to have a convenient time area between 0,0170-0,0180 and blowdown between 0,0013-0,0014 (road race).

So all of this means that from the exhaust port's flow area we can't deduce to the area of the passage? It is interesting but now I'm a little bit confused because I thought I knew the secret.:-)

Forgi,

What really counts is blowdown.
But discharging of the burned gases may not be complete until BDC.
In this case you get 'short circuiting' of the fresh charge from the transfer ports into the exhaust.
By using auxiliar exhaust ports you can improve blowdown quite a lot.
So that you might be able to raise the exhaust's 'floor'.
This helps improve blowdown flow, as seen on a flowbench.
In 2007 we started to raise the underside of the exhaust port.
The first results were very promising!
But at the end of 2007 I retired, so I could not finish what I started.
The idea was to raise the exhaust underside as much as possible until power dropped.
And then, with a smaller exhaust port underside it might have been possible to widen the A-ports more
without losing the fresh charge into the exhaust.
The ideal situation would, of course, be that all the burned gases are discharged from the cylinder before
the transfer ports start opening.
So it is difficult to have too much blowdown.
But in trying to achieve enough blowdown you can arrive at a too high exhaust port.
Which first causes power loss at low revs, and if exaggerated still more also a loss of max. power.
Because of shortening the power stroke.

Jan,
Can I ask why exhaust control valves were only used on the main exhaust port in the RSA?I would guess that the auxiliary exhaust ports would open at about 95 degrees BBDC to maintain good midrange power.If exhaust control valves were used on the auxiliary ports then they could be opened 4 or 5 degrees earlier increasing the blowdown area and possibly allowing the A-port timing to be increased.
Thank you for sharing your knowledge with the forum.
Garry

Frits Overmars a écrit:

Forgi a écrit:

Frits Overmars a écrit:: Forget about the mean area of the exhaust port, Forgi. Look at the blowdown area.

So are you telling me that the exhaust port's time area doesn't mind? :-) Only the blowdown what is important?

Yes!

Thank you Frits! Well if only the blowdown matters then can you tell me why the bottom of the exhaust port and the top of the transfer ports are not at the same height in case of the modern engines?

It would be logical because this way the fresh mixture couldn't flow out from the exhaust or at least the risk of this would be minimal. Of course if we would like to make an exhaust port like that the appropriate size of the blowdown is crucial.

For example if we take an RSA or RSW Aprilia engine and the exhaust port would be at the same height as the top of the transfer port the area would be 800-820 m2 ( 32mm diam.) and not 1200-1220 mm2 (39mm diam.). In this case the exhaust passage would be proportionally smaller and the exhaust duct also would be about 32 mm as a minimum.

Dear Jan, by chance haven't you done tests like this?

Forgi a écrit:

Frits Overmars a écrit:

Forgi a écrit:

Frits Overmars a écrit:: Forget about the mean area of the exhaust port, Forgi. Look at the blowdown area.

So are you telling me that the exhaust port's time area doesn't mind? :-) Only the blowdown what is important?

Yes!

Dear Jan, by chance haven't you done tests like this?

Jan! I can see that you have already answered a few questions of mine. Thank you for your detailed explanation! :)

Frits, can you tell me more about the additive manufacturing process you're going through to make cylinders? Who are you using for the work and can any type of aluminum be used? I've been researching this as a way to make some prototypes I want to hear your thoughts on it. Thanks.

Paul

PVO a écrit:: Frits, can you tell me more about the additive manufacturing process you're going through to make cylinders? Who are you using for the work and can any type of aluminum be used? I've been researching this as a way to make some prototypes I want to hear your thoughts on it. Thanks.

Paul

Hi Paul!

for my cylinder...I have contacted Marchetto-group

[Vous devez être inscrit et connecté pour voir ce lien]

i sent them 3D drawing

[Vous devez être inscrit et connecté pour voir cette image]

Nombre de messages : 112 Localisation : Germany Date d'inscription : 07/02/2012

may i ask how much it was to prototype one? i know it's normally crazy expensive...so was it already in thousand range or hundreds for one?

koenich a écrit:: may i ask how much it was to prototype one? i know it's normally crazy expensive...so was it already in thousand range or hundreds for one?

the price is proportional to the size...
These are minibike cylinder, and they are small!!!
the quantity is little influential...
i have spent 200 euro everyone

Nombre de messages : 112 Localisation : Germany Date d'inscription : 07/02/2012

SB07 a écrit:

koenich a écrit:: may i ask how much it was to prototype one? i know it's normally crazy expensive...so was it already in thousand range or hundreds for one?

the price is proportional to the size...
These are minibike cylinder, and they are small!!!
the quantity is little influential...
i have spent 200 euro everyone

i know normally the prices - we sometimes do prototypes in stereolitography, but this price is a bargain!

koenich a écrit:

SB07 a écrit:

koenich a écrit:: may i ask how much it was to prototype one? i know it's normally crazy expensive...so was it already in thousand range or hundreds for one?

the price is proportional to the size...
These are minibike cylinder, and they are small!!!
the quantity is little influential...
i have spent 200 euro everyone

i know normally the prices - we sometimes do prototypes in stereolitography, but this price is a bargain!

You called Marchetto-group and ask with Claudio Preatto... and speak you are Brutti Stefano friend!!! aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 771973

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 771973

Nombre de messages : 112 Localisation : Germany Date d'inscription : 07/02/2012

first i need a drawing and some ideas aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 349660

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 349660

or you do yours for 56 x 56 studs...

the drawing you posted, is it with some plus measurements for machining it after prototyping? cause 24,4 from exhaust port to top would give a really low exhaust timing...

koenich a écrit:: the drawing you posted, is it with some plus measurements for machining it after prototyping? cause 24,4 from exhaust port to top would give a really low exhaust timing...

This is false!!! lol!

the misure are dependent from stroke!
the head is 2mm internal in the cylinder... this is as 22.4mm aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 771973

everything has a reason ... aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 809262

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 809262

Something like this, el castor!!

[Vous devez être inscrit et connecté pour voir cette image]

This is a girdle fitted to a Rotax 257 to prevent cylinder cracking

Best Regards

Ian

Nombre de messages : 112 Localisation : Germany Date d'inscription : 07/02/2012

SB07 a écrit:

koenich a écrit:: the drawing you posted, is it with some plus measurements for machining it after prototyping? cause 24,4 from exhaust port to top would give a really low exhaust timing...

the misure are dependent from stroke!
the head is 2mm internal in the cylinder... this is as 22.4mm aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 771973

everything has a reason ... aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 809262

i was assuming it'll be a 50cc engine so usually they don't differ much in stroke and conrod length. but didn't think of head going in the cylinder aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 800210

aprilia - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 21 800210

Nombre de messages : 98 Localisation : Italy Date d'inscription : 30/10/2012

hello at all

Jan or Frits did you ever tried a timing like 86° 160°? because all had only 150° bTDC beginning opening??

Another question:

if the inlet goes with the turning direction of the crankshaft, it's better to keep the crankcase open over the crankshaft, or is it better to keep it closed?
has someone tried the difference??

thanks
manuel

Manuel we tested 160 opening timing. It did not help or hurt power at the usable powerband but made slightly less power at low rpm and made starting more difficult. 150 seems to be the magic number. 145 made less power all through the powerband.
Our engine has a design drawback in that one inlet port opens from the bottom and one opens from the top. The one that opens from the top has less airflow and I suspect less power than the one that opens from the bottom.

Frits Jan, I have a question. The RSA250 twin. Was it a 90 degree, big bang or 180 degree firing motor? Would a motor that fires 120 degrees make as much power as a 180 degree firing motor? The problem with our Rotax rotary valve twin cylinder motor is that the rotary valve controls both inlets. Since it is a 180 firing motor the inlets ports need to be placed 180 degrees apart. This means they are located low on the crankcase. The problem is that the crankshaft gets in the way of the port unless you angle it up into the motor. My idea was to design a 120 degree firing rotary valve twin. This would allow me to move the ports higher on the case allowing much straighter and less restricted entry into the case.
What are your thoughts on this?
Howard..

Forgi a écrit:: ...l if only the blowdown matters then can you tell me why the bottom of the exhaust port and the top of the transfer ports are not at the same height in case of the modern engines?

I do not consider them modern engines Wink

.

Citation :: For example if we take an RSA or RSW Aprilia engine and the exhaust port would be at the same height as the top of the transfer port the area would be 800-820 m2 ( 32mm diam.) and not 1200-1220 mm2 (39mm diam.). In this case the exhaust passage would be proportionally smaller and the exhaust duct also would be about 32 mm as a minimum.

That is a very accurate assessment, Forgi. The RSA's blowdown area is 812 mm². But the diameter of the exhaust passage also strongly effects the frequency of the engine's Helmholtz resonance; 32 mm would yield too low a frequency.

PVO a écrit:: Frits, can you tell me more about the additive manufacturing process you're going through to make cylinders? Who are you using for the work and can any type of aluminum be used? I've been researching this as a way to make some prototypes I want to hear your thoughts on it.

My cylinders were made here: [Vous devez être inscrit et connecté pour voir ce lien] . Any type of aluminium can be used; if you wish, they can also produce cylinders in inox steel or even in titanium. But you have to take into account the suitability of the base material to be coated with nikasil, and the best material for that is AlSi12.

Howard Gifford a écrit:: Frits Jan, I have a question. The RSA250 twin. Was it a 90 degree, big bang or 180 degree firing motor? Would a motor that fires 120 degrees make as much power as a 180 degree firing motor? The problem with our Rotax rotary valve twin cylinder motor is that the rotary valve controls both inlets. Since it is a 180 firing motor the inlets ports need to be placed 180 degrees apart. This means they are located low on the crankcase. The problem is that the crankshaft gets in the way of the port unless you angle it up into the motor. My idea was to design a 120 degree firing rotary valve twin. This would allow me to move the ports higher on the case allowing much straighter and less restricted entry into the case.
What are your thoughts on this?
Howard..

Firing at 90° seems to work very well I heard.
Would this be a possibility for your engine?
The RSA250 is a big-bang with the cylinders at 90°.
And the crankshafts coupled by gears, which costs some power.

Howard Gifford a écrit:: Manuel we tested 160 opening timing. It did not help or hurt power at the usable powerband but made slightly less power at low rpm and made starting more difficult. 150 seems to be the magic number. 145 made less power all through the powerband.
Our engine has a design drawback in that one inlet port opens from the bottom and one opens from the top. The one that opens from the top has less airflow and I suspect less power than the one that opens from the bottom.

I thought about this when we designed the RSA.
And made te inlet open from the bottom!

Manuel Rainer a écrit:: hello at all

Jan or Frits did you ever tried a timing like 86° 160°? because all had only 150° bTDC beginning opening??

Another question:

if the inlet goes with the turning direction of the crankshaft, it's better to keep the crankcase open over the crankshaft, or is it better to keep it closed?
has someone tried the difference??

thanks
manuel

It is better to keep the crankcase open.
Seen in 1974!

Nombre de messages : 30 Localisation : Greece Date d'inscription : 09/07/2011

Jan Thiel a écrit:: Herbert Rittberger once had the best solution I think.
Take a look at his Krauser engines!
Also the solution used on the Morbidelli/MBA was good.
A combination of these 2 systems would be ideal!
For the bolts Dilavar would be the best material.
It has the same expansion rate as aluminium and was used for Porsche's headbolts!

This must be the engine you refer to, eh Jan?
The article is in dutch, but pics in english, as Frits says. I let Chrome aut-translate it in English and I read it super ok.

[Vous devez être inscrit et connecté pour voir ce lien]

[Vous devez être inscrit et connecté pour voir cette image]

edit: [Vous devez être inscrit et connecté pour voir ce lien] this is in pdf form if someone wants to save it to his pc

CRECY a écrit:

Jan Thiel a écrit:

Forgi a écrit:

Frits Overmars a écrit:: Forget about the mean area of the exhaust port, Forgi. Look at the blowdown area.
What I wrote in the seventies, is 35 years old! And what I showed in the exhaust concept that I posted some time ago, is an extreme simplification, only meant to help beginning tuners on their way.

It is quiet interesting Frits! So are you telling me that the exhaust port's time area doesn't mind? :-) Only the blowdown what is important? Well I always intend to make the whole exhaust port to have a convenient time area between 0,0170-0,0180 and blowdown between 0,0013-0,0014 (road race).

So all of this means that from the exhaust port's flow area we can't deduce to the area of the passage? It is interesting but now I'm a little bit confused because I thought I knew the secret.:-)

Forgi,

What really counts is blowdown.
But discharging of the burned gases may not be complete until BDC.
In this case you get 'short circuiting' of the fresh charge from the transfer ports into the exhaust.
By using auxiliar exhaust ports you can improve blowdown quite a lot.
So that you might be able to raise the exhaust's 'floor'.
This helps improve blowdown flow, as seen on a flowbench.
In 2007 we started to raise the underside of the exhaust port.
The first results were very promising!
But at the end of 2007 I retired, so I could not finish what I started.
The idea was to raise the exhaust underside as much as possible until power dropped.
And then, with a smaller exhaust port underside it might have been possible to widen the A-ports more
without losing the fresh charge into the exhaust.
The ideal situation would, of course, be that all the burned gases are discharged from the cylinder before
the transfer ports start opening.
So it is difficult to have too much blowdown.
But in trying to achieve enough blowdown you can arrive at a too high exhaust port.
Which first causes power loss at low revs, and if exaggerated still more also a loss of max. power.
Because of shortening the power stroke.

Jan,
Can I ask why exhaust control valves were only used on the main exhaust port in the RSA?I would guess that the auxiliary exhaust ports would open at about 95 degrees BBDC to maintain good midrange power.If exhaust control valves were used on the auxiliary ports then they could be opened 4 or 5 degrees earlier increasing the blowdown area and possibly allowing the A-port timing to be increased.
Thank you for sharing your knowledge with the forum.
Garry

Somehow raising the auxiliar ports did not work well.
It destroyed midrange power.
And did not give more max. power!

Closing the auxiliary ports and ducts only gave more power below 9000rpm
And lost power at 10.000.
So we decided that there were not enough advantages in putting a valve on them!

Vagelis a écrit:

Jan Thiel a écrit:: Herbert Rittberger once had the best solution I think.
Take a look at his Krauser engines!
Also the solution used on the Morbidelli/MBA was good.
A combination of these 2 systems would be ideal!
For the bolts Dilavar would be the best material.
It has the same expansion rate as aluminium and was used for Porsche's headbolts!

This must be the engine you refer to, eh Jan?
The article is in dutch, but pics in english, as Frits says. I let Chrome aut-translate it in English and I read it super ok.

[Vous devez être inscrit et connecté pour voir ce lien]

[Vous devez être inscrit et connecté pour voir cette image]

edit: [Vous devez être inscrit et connecté pour voir ce lien] this is in pdf form if someone wants to save it to his pc

Yes, this is what I meant!
Such a design gives ample space for cooling, and the cylinder is not stressed!
With a horizontal cylinder there are no problems.
With a more vertical cylinder it might become difficult taking it off, because of the long bolts.
If you can find a photo of an MBA or Garelli crankcase you will see the solution of this problem.

Ian Harrison a écrit:: Something like this, el castor!!

[Vous devez être inscrit et connecté pour voir cette image]

This is a girdle fitted to a Rotax 257 to prevent cylinder cracking

Best Regards

Ian

This is a very good idea to keep cylinders from cracking.

» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)
» [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)
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