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

FOS software download link, valid until February 17, 2022

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

I wrote these programs in the course of over five decades for my own personal use and I never bothered to make them user-friendly, so you may have to do some experimenting on your own, as I will not have time to answer questions.
The lot runs on MS-DOS 6.2 or Windows 98 (I recommend Win98SE) so either dig up an old computer or use an emulator. On my Win10-laptop I use VMWare Player.
I advise against DOSBox 0.74 because that is essentially a stripped-down version of MS-DOS 5; it will run some of the programs, but not all of them.

Thanks Frits!

Dear Mr.Frits. Thank you for your advice always.
1) Would you please advise about merit cylinder B & C port open early than A port like RSA (3 EX port)
but RS125RW (Bridge port ) A port open earlly. what is main idea of this title or B & C early open ,
it 's better scaveging correct?

2) Tranfer port passes ratio of A,B,C port shall 1.1 or more better? / what 's importance concept of this title,

Thank you for you share idea / regards

Thanks Frits

Bruno

Hi Frits,
My query concerns events during combustion in a typical race engine. From the point when turbulent burning begins is that burn rate constant or does it vary during its progression through the chamber to its completion at the cylinder wall. Indeed is all of the combustible mixture in the chamber actually consumed when the engine is running a peak efficiency? I know there are many variables like fuel type, chamber profile and compression ratio and so on. This is one of those areas where the average lay person has great difficulty in imagining and in grasping the combustion process. Hope you can offer some insight.
Thank you, Mel.

pojoran a écrit:

1) Would you please advise about merit cylinder B & C port open early than A port like RSA (3 EX port) but RS125RW (Bridge port ) A port open earlly.   what is main idea of this title or B & C early open , it 's better scaveging correct?  
2) Tranfer port passes ratio of A,B,C port shall 1.1 or more better? / what 's importance concept of this title. 

Dear Pojoran, The A-transfers in the Aprilia RSA were a fraction lower than the B- and C-transfers because they had to make room for the auxiliary exhaust ports. Honda used to do it the other way around, but then Honda also used transfer ducts with an decreasing inner radius, whereas Aprilia used a constant inner radius that gave much better flow. I still do not understand why Honda sticked to their layout instead of simply copying the Aprilia layout.
I am afraid that I do not quite understand your second question, Pojoran.

melvyn trevor a écrit:

Hi Frits, my query concerns events during combustion in a typical race engine. From the point when turbulent burning begins is that burn rate constant or does it vary during its progression through the chamber to its completion at the cylinder wall. Indeed is all of the combustible mixture in the chamber actually consumed when the engine is running a peak efficiency? I know there are many variables like fuel type, chamber profile and compression ratio and so on. This is one of those areas where the average lay person has great difficulty in imagining and in grasping the combustion process. Hope you can offer some insight. Thank you, Mel.

The burn rate increases as the pressure and especially the temperature in the combustion chamber increase.
Whether all the mixture is consumed, depends on its Lambda value. The amount of power that we can extract, depends on the amount of oxygen in the cylinder. It is easy enough to increase the amount of fuel, but the amount of inhaled air is limited by a whole lot of factors, like exhaust blowdown and transfer time.areas, pipe resonance and flow coefficients, and in order to make sure that all present oxygen is really being used, we make the mixture about 15% over-rich.
Lambda-values around 0,85 give the best power. So at peak engine efficiency all air may be consumed, but not all fuel.

The homogeneity of the mixture plays a role as well. Fuel drops that haven't had time to evaporate, may not burn completely, even if there would have been sufficient oxygen. And mixture that has been hiding in relatively cool places like the squish zone and the circumferential gap between clinder and piston above the piston ring, may not take part in the festivities either.

Hi Frits ,
Many thanks for your swift and comprehensive reply, you have clarified things for me.
Mel.

Frits Overmars a écrit:

pojoran a écrit:

1) Would you please advise about merit cylinder B & C port open early than A port like RSA (3 EX port) but RS125RW (Bridge port ) A port open earlly.   what is main idea of this title or B & C early open , it 's better scaveging correct?  
2) Tranfer port passes ratio of A,B,C port shall 1.1 or more better? / what 's importance concept of this title. 

Dear Pojoran, The A-transfers in the Aprilia RSA were a fraction lower than the B- and C-transfers because they had to make room for the auxiliary exhaust ports. Honda used to do it the other way around, but then Honda also used transfer ducts with an decreasing inner radius, whereas Aprilia used a constant inner radius that gave much better flow. I still do not understand why Honda sticked to their layout instead of simply copying the Aprilia layout.
I am afraid that I do not quite understand your second question, Pojoran.

Dear Frits thank you for your advice.
My inquire No.2 is passses ratio of area port window on cylinder wall vs entry area of transfer port shall be 1.1 or more better ?
what is main idea of this matter. what 's best ratio of A,B,C port on your idea and experience.
Thank you

Dear Mr. Mingret, I tried to quote and answer your question, but quoting it is impossible for some reason.
If the exhaust power valve is opening at 13000 rpm, something is wrong. It should already be opening at 10.500 rpm and be fully open before 13000 rpm. It is not clear to me what is actually happening, so I cannot answer your question "how it's possible that I managed to get power before this rpm".

jfn2 a écrit:

Hello quod and probation:
At what RPM was your low rpm trial and what RPM was your high rpm trial? And about the channel shapes, what exactly was the outcome and what did you learn from the outcomes?
Did the piston window have a axial roof also and did the axial roof angle of the c-port match closely with what Frits suggests?
Thank you, Jeff

Hallo Jeff!
So, we are dealing with two different concepts here. One is an additional C (D) duct fed through a piston window and scavenging channel milled into the rear cylinder wall.
And the other is an additional channel that connects directly from the intake port into the cylinder.
Unfortunately, I no longer have any documentation (drawings, photos) or test bench records, but I had no idea that this would be of interest again. So, some(long) time ago, I destroyed several kilos of paper.
I found some notes, but unfortunately, I can't allocate them all any more.
So with the piston window, which is suitable for a powerful -C (D)-channel, I had to make some modifications to the piston as well as to the cylinder.
I regrettably don't have exact documentation on this, but the torque curve has improved from about 5500 to about 8200rpm. Furthermore, I mentioned that the peak power was not increased, this is not quite true because in the together game with additional modifications I had gained revs and peak power.
The second concept was the direct scavenging duct from the intake duct.
The good thing about this configuration was I didn't have to modify the piston. But I had to work on the cylinder in the same way.
As far as I can remember, these tests were more lengthy. The power increase was then at about 9500 to 11000rpm. But mind you, with all these adaptations of an additional overflow cal, there is some effort involved.
Greetings Cara

Hello Cara:
Thank you very much for your reply.
I understand about the two different concepts. I used the first concept a lot of times back in the 70's and 80's with dirt bikes. What I'm working with now is a old 70's engine that is piston ported with only 4 transfer ports and room for a c (d) port if I can figure out how to get one in the space. I have no room under the ring land for a window in the piston to use with the first concept.
If I understand the second concept correctly, it is somewhat like using the 24/7 reed setup that Frits and Wobbly refer to only it's effect is regulated by the height of the transfer channel in the bore, ( 75%-95% height of the other transfer channels). Mainly the ability to start the engine and get it to rev to a rpm level for the pipe to start to work.
The engine is a parallel twin with a bore of 62mm and a stroke of 55.6mm. Very similar to a TZ 350. The working rpm is 10-10,500 and the lowest rpm would be 6-6,500 for the start of the race. I understand I could just add reeds but I would like to try this first. This engine is in a snowmobile and uses a CVT drive.
Your thoughts, ideas and insights would be appreciated.
Thanks, Jeff

Hallo Jeff!
I will report back to you everything I remember.
The TZ 350 cylinders, four or six ports, all have very little cylinder wall thickness, about 7 mm, which is too little for a productive – C/ D overflow channel, and therefore I cut out a window in the cylinder outer wall, (water jacket) above the intake flange. This made it possible to carry out extensive build-up welding directly on the cylinder.
I did this with every concept.
In the case of the piston window variant, I also made a build-up weld at the top of the intake duct (nose, protrusion), which made it possible to create a relatively large, wide duct with a sufficient radius for the rising C/D overflow. And at this point I widened the intake channel to the maximum.
The piston window was milled to about 1 mm below the piston ring, so I had to move the pin for the piston ring on the original Yamaha pistons. Later I used Mahle pistons, where this change was no longer necessary.
With this variant, there were none except the usual starting problems.
In addition, the power delivery was very noticeable in the middle and higher revs with optimized ignition timing.
I made many more minor to major changes after that, with relatively good performance results.
I assume that you will not be able to get by without welding work on your cylinder.
The second type of modification, the direct channel between the intake port and the cylinder, involved an intensive and lengthy series of tests.
I mean, it would become too much here if I went into everything else I know, so I will report on it a little more abbreviated.
So, I tested different sizes and lengths with different carburettors. The best result was at about 92% elevation, I think, and with a 40 flat slide carb. With these, at the carburettor inlet, I pulled in a horizontal (horizontal) intermediate base made of synthetic or aluminium sheet, which reached up to the carburettor slide. I then tested several synthetic carburettor flange spacers and the best piece was about 15 mm long ,thick, I think I remember.
This synthetic flange spacer, about 15 mm thick, I tapered inside from about 39 (40) mm to 35 mm, narrowed with a gentle radius to the narrowest point. This narrowing then ended after approx. 15 mm towards the cylinder, with a sharp-edged finish. This created a gentle diffuser, funnel coming from the carburettor towards the cylinder.
The carburettor adjustments were very tedious according to my memories.
Again, the other changes reacted very differently. The most noticeable reaction was with a certain exhaust configuration and to a larger crankcase volume. I turned the original crankshafts down about 1.5 mm on the inside and about 0.5 mm on the outside. It resulted in an improvement. As a result, I used Höckle crankshafts (with narrower crankshaft cheeks and better connecting rods). The increase in revs could no longer do any harm, they were expensive, but good.
With the TZ four-channel cylinders, I concentrated on the B-channels.
I used sleeves in the stud boltholes to gain additional material, which I used to enlarge the rear towards the intake. The duct shape on the rear side wall was given a large radius. I also corrected the duct exit angles backwards over the centre of the cylinder. I used Devcon for this, which I mixed with fine aluminium chips. And, of course, the same procedure for the C-channel on these cylinders.
I mean, to get rich power, I suggest you try to reach; 11000rpm, at about 12–13 degrees pre-ignition.
Combustion chamber with slightly less compression and a squish area of 0.9–1 mm spacing. Let the spark plug protrude approx. 1 mm into the combustion chamber and bevel the protrusion in front of the electrode.
Do not let the operating temperature rise above 60 degrees.
I have radically changed the water routing on the TZ 350s.
New exhaust systems, don't just calculate, but modify and test for the particular application, there is a lot, a lot of potential there.
Enlarge the crankcase.
And, and, and...........
Nevertheless, Jeff, I must point out to you that all of this only works properly and well in a conglomerate of changes and modifications that can then, as a whole, lead to a usable and drivable power delivery. Unfortunately, I do not know your cylinders and therefore do not know whether all this is relevant to your cylinder.
If my report seems too confused for you, I am happy to go into more detail if I still know about it.
Greetings Cara

Great story, Cara. This reads like a thriller   . From what period does this history date?

Quod et probat a écrit:

All of this only works properly and well in a conglomerate of changes and modifications.

This reminds me of a description I once posted:
"A two-stroke engine is like a combination lock with ten digits. If you get nine out of the ten numbers right, nothing happens; you don't even have a way of knowing whether you got them right at all."

This thriller, as you call it, is of course from the -TZ 350 period from 1972~73 to 1982.
Yes, you are absolutely right with these -10 point numbers.
Yes, I have experimented a lot – and I don't dare report everything because at my age I feel it would be better not to be called a weirdo yet (or again).
Some people used to smile at me because of my modifications and changes, I think because they didn't understand some things in my opinion. Many of these complainers simply bought what the masses had with a lot of money and didn't have to think much.
My finances were very limited at that time, so not everything could be brought to perfection, to maturity and to completion, although some things worked quite well for a long time.
I believe that if there were no so-called spinners, there would be no two-strokes.
Of course, you can embellish this sentence.

Quod et probat a écrit:

I have experimented a lot – and I don't dare report everything because at my age I feel it would be better not to be called a weirdo yet (or again).

I know all about being called a weirdo. For example I vividly remember the reactions when I expressed my preference for low primary compression ratios fifty years ago, and that was just one of the many ideas that made the hairs of the 'experts' at that time stand on end. Half the two-stroke community still seems to think I'm crazy but the older I get, the less I care.
So please share your experience and make us happy

Yes, please Cara !

Frits Overmars a écrit:

Quod et probat a écrit:

I have experimented a lot – and I don't dare report everything because at my age I feel it would be better not to be called a weirdo yet (or again).

I know all about being called a weirdo. For example I vividly remember the reactions when I expressed my preference for low primary compression ratios fifty years ago, and that was just one of the many ideas that made the hairs of the 'experts' at that time stand on end. Half the two-stroke community still seems to think I'm crazy but the older I get, the less I care.
So please share your experience and make us happy

I am pleased that you understand me.
But it saddens me very much that it has happened to such a genius like you.
That with the low primary compression ratio is a meaningful and directional insight axiom of yours, that the development process in the holistic view is a meaningful aspect.
For example, when I swapped the outer cylinders on the Kawasaki H1 500, 50 years ago and subsequently converted it to water cooling, cylinders and heads, with a (at that time) large radiator, many know-it-alls grabbed their heads and announced that this would have no effect.
This is just one of many examples of many innovative technical solutions, over several decades, that were dismissed as useless with the prepotency of those supposedly in the know.
Therefore, I can understand very well how you felt.
What surprises me very much is that there is, we write -2022- an interest for 2 strokes.
Normally, I should be happy about that, but maybe it's just a dream.
However, I must confess that when dreams came true for me, an indescribable feeling of happiness arose afterwards, e.g. when an engine that I had tuned achieved success in a race, or when I started my TZ 750 for the first time. ....
Well, the dreams and the realities are so much like 2 strokes to wrongstrokes.

Any time you try something not in accordance with the current orthodoxy, you are treated of crazy, stupid or something like that.
For some reason, most of people, although they will defend against this idea, are super conformist.

But on this topic you have already a bunch of non-conformist people, so, please tell us about your TZ ideas, I'm impatient to read what you did.

Hello, all you intellectually disengaged people out there!
The system is not there to promote innovative people, but to promote bondage (dependency) and mass dumbing down.
Thank goodness for the thread – TZ 350 – as well as about some other 2 Strokes.
I don't even know where to start.
So, I'll follow on from what I've already written for -Jeff-.
As a result of the widening of the intake duct, I have also inserted aluminium bushes in the stud bolt holes on the exhaust side.
The stud bolts were lengthened and the shank nuts shortened and adjusted.
Then I made additional exhaust openings on the side. Of course, I broke through to the aluminium bushings and the extended stud bolts when milling out the ducts, this did not result in any disadvantage but improved the performance considerably.
When I changed to the – MAHLE – pistons, which had a full piston skirt, I made the extra exhaust ports largely. To prevent short-circuiting as much as possible, I used a short piston pin and then made an aluminiumplug and fine threaded the piston pin hole and screwed it in. Didn't use that for long, though because making the thread was relatively tedious. It also added weight (oscillating mass) and this procedure didn't feel very safe to me. I was always afraid of mechanical cold deformation. But it still worked.
I also mounted an aluminium hump on the inside of the exhaust duct on the underside. It started about 2 mm from the lower edge of the exhaust opening in the direction of the exhaust. The bottom side was, of course, adapted to the duct shape and the top side was flat, approx. 8 mm high and ran in a gentle curve, approx. 25-30 mm long, towards the end of the exhaust duct.
I fixed this with two M3 screws left and right from the outside next to the centre support. I added Devon to the underside and then screwed it on. Never had any problems with it.
I shortened the cylinder shank that goes into the crankcase by about 10 mm to prevent it from constricting. Volume was also gained by this, it was little, but still.
On the cylinder wall on the exhaust side, three vertical grooves about 3 mm wide were milled with the ball cutter. These extended from the cylinder shank to the underside of the piston ring at -BDC-. Due to the additional lubrication, the engine had one problem zone less.
On the four-channel cylinder, I had milled a groove along the outer wall of the channel exactly next to the partition wall to the B-channel with an approx. 5 mm ball cutter inside the A overflow channel. This was approx. 3 mm deep at the duct inlet and only approx. 0.5 mm high at the flushing duct roof at the outlet and aligned in such a way that the fresh gas flow of the -A-ducts, most likely, met approx. 15–18 mm before the -C-duct. I hoped that this acted as a kind of -guiding jet-. According to the piston picture, this assumption was approximately correct.
This arrangement and the radical widening of the -B-channel, which ended in the cylinder with a large bend, radius, and with a narrow web towards the C-channel. This enlargement could be realized by the aluminium bushings in the stud bolt holes. This also worked with the six-channel.
Mind you, this only worked in conjunction with the overlay welding over the inlet port.
I was very satisfied with the torque curve and response of the 4 /5 channel cylinders.
So, now I have to desulphurate my synapses.
I would like to point out that I will not be held responsible if you tear your hair out (balding) or laugh your head off because of my historical pastimes!
Short break, come back soon.
Cara

Great, thanks for sharing your experiences, Cara !

Is it possible to share some drawings or sketches? So even the non English speaking understand.

Cara, thanks! I hope you have recieved enough credit in your lifetime for your remakable communication skills, you are as entertaining as enlighening.

carlovitch1 a écrit:

Great, thanks for sharing your experiences, Cara !

Is it possible to share some drawings or sketches? So even the non-English speaking understand.

Yes, I thought that would happen. Unfortunately, I have to disappoint you. I have already explained above that I could not foresee that there would be such interest in 2-strokes. Years ago I disposed of several kilos of documents. These were sketches, drawings, test bench protocols, photos because I was not prepared for this interest.
But perhaps I can answer certain questions in more detail.
I was inspired to pass on my meagre knowledge of my long-term memory, and I will be happy to do so as far as I can.

yeahhim a écrit:

Cara, thanks! I hope you have recieved enough credit in your lifetime for your remakable communication skills, you are as entertaining as enlighening.

Recognition is one thing. I haven't worked towards or hoped for any pats on the back all these years. I was always against indoctrination and wanted to unpack and understand the supposed mysteries of physics (technology).
I have great respect, here, from a physicist and also from a technician who have brought the two-stroke universe with its (dark) energy closer to us. Unfortunately, I perceived these insights into this evolution much too late. This technical lettering and poetry on the subject of 2 Strokes shows us how far-reaching, complex and causal the subject of 2 Strokes can be. Simply phenomenal.