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

I speak to the photo posted, not to question the modern bases of two stroke head...

GtG001 a écrit:

GtG001 a écrit:

Hi Jan,
Was there much HP gain from extending the auxiliary exhaust ports below the front of transfer port A? – (the side closest to the main exhaust)


Thanks for your answer in advance.
Regards
Allan.

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

We tried it little by little.
What you see on the photo was the limit.
It gave a good improvement.

romeuh80 a écrit:

For everybody here tuning cylinders, what was the result of this?

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

I did it twice, I notice the spark a bit leaner, I ajust but not sure if improved something, I don't have a dyno.

The difference was a couple of tenth's HP

Hi again.

Thanks for the answer

Should a 2 stoke ram air system only work properly with power jet?
What is a good size for power jet in relationship with main jet size, 1/3 of an alone previous main jet?

Many Thanks

Hello,
I'm a Mechanical Engineering Student working on two stroke engines for 8 years now as a hobby.
My current test engine is a CR 125 in the same Bike. I started with Simson and MZ engines. Quite cheap to make experiments for learning.

Now I have a question about the Aprillia B-Port. I remember Frits or Jan saying that a duct should just change his size in one dimension.
This does not apply anywise in the B-Port. I remember also the fact that the B-Port is a relict from an old crankcase and also restricted
by the stud pattern. So first question why does a winged B-Port not working better...you could have the vertical angles (I asume about 90° and 150°
which I believe has shown the best performance at Aprilia) with a constant area change which should make the flow much better (my thoughts).
And the second is if it not would be better to make the B-Port duct intake larger (about 1,2x port area) if we make our own cylinders
and can choose a studpattern like we want?

Thanks for all the facts you both have released! It helped me a lot in my engine...still suffering on part throttle detonation on the CR but there is still a lot left!
Deepest thanks!

nine-thirtysix a écrit:

...I remember Frits or Jan saying that a duct should just change his size in one dimension.

That would mean that for example in a rectangular duct of 20 mm x 30 mm only the 20 mm dimension or only the 30 mm dimension should be allowed to change, but not both.
But I never said such a thing; I said that a duct should not change direction in more than one plane.

Citation :

...why does a winged B-Port not working better..

What do you mean by a winged B-port?

Citation :

would it not be better to make the B-Port duct intake larger (about 1,2x port area) if we make our own cylinders and can choose a studpattern like we want?

Yes. But if you do that in an Aprilia cylinder, the scavenging balance, which is an equilibrium of port timings, port widths, port directions and duct flow characteristics, will be disturbed.
Jan has tried this of course; he has tried everyting .

Citation :

I said that a duct should not change direction in more than one plane.

I couldn't find the post to quote it...sorry.

Citation :

What do you mean by a winged B-port?

I mean a wing through the B-port duct. Now the duct start about 0,8 of the port area rises to let's asume 1,5 of the port area
and the went down to the port area. Now you could split the duct on the particular lenght to get a overall Area of 0,9 instead of 1,5.
So the Wing would split the duct just in the area where it is probably not good for flow (my thoughts) put with the same vertical angles.
Don't know how to describe it better...

romeuh80 a écrit:

Hi again.

Thanks for the answer

Should a 2 stoke ram air system only work properly with power jet?
What is a good size for power jet in relationship with main jet size, 1/3 of an alone previous main jet?

Many Thanks

A twostroke ram air system also works without a powerjet. as long as you put the tank breather pipe into
the airbox.
But there is indeed some problem.
At high speed the air pressure rises, so you need a richer carburation.
With this richer carburation it will be too rich at low speed.
Here a powerjet helps a lot, you need a gear-related fuel curve as well as a rpm-related one.

With the earlier open/close powerjets we used a main jet of 230 and a powerjet of 45.
Later we had the 'proportional' powerjet wit a main jet of 220 and a powerjet of 120

koenich a écrit:

i think he was trying to say that every sharp edge in a 2 stroke engine is not good and with logical thinking you'll know why...

With 2 exceptions:

1 In the combustion chamber a shap edge from squish to dome proved best.
2 The top edge of the A and B transfers had to be as sharp as possible.

As this is my first post in this forum - I think it should be to thank both Frits & Jan for taking the time to educate many of us on some of the finer points of the 2 stroke "mystery" - I think it was probably my "lucky day" to find this thread... (although it has cost me a couple of extra days I had not planned to read all the posts in this & the previous Part of the thread )

I do have a few questions of my own in relation to an older 2 stroke design - but I will start a new thread for that (In the Moteurs section) - and hope for a few moments of your valuable time....

I hope no one else here minds too much that I can only post in English - but my schoolboy "French" language skills are very limited

nine-thirtysix a écrit:

Citation :

What do you mean by a winged B-port?

I mean a wing through the B-port duct. Now the duct start about 0,8 of the port area rises to let's asume 1,5 of the port area and the went down to the port area. Now you could split the duct on the particular lenght to get a overall Area of 0,9 instead of 1,5. So the Wing would split the duct just in the area where it is probably not good for flow (my thoughts) put with the same vertical angles. Don't know how to describe it better...

I still don't get it. Do you mean a vertical wing, a horizontal wing, a curved wing? Better make a little sketch, 936.
And why would you want to put a wing in? To improve the flow through the B-duct? Enlarging the entry area will do that, and it will cost power.

hallo

a few pages before someone asked about the negative squishband and the answer was:

negative squishband = boom

what does it mean? more powerful? can someone please explain this again exactly. if there is more, where and how much?

thanks Manuel

It means that your motor will break, as you'd expect from hammering the piston against the head 200 times / second.

Jan Thiel a écrit:

With 2 exceptions:

1 In the combustion chamber a shap edge from squish to dome proved best.
2 The top edge of the A and B transfers had to be as sharp as possible.

Did you ever have probelms with rings on the sharp A/B port windows, did you just leave the as plated finish or was it dressed in some way. "Stucco Verde" works a treat and is a pleasure to work with as well.

Institute of TwoStrokes a écrit:

Jan Thiel a écrit:

...The top edge of the A and B transfers had to be as sharp as possible.

Did you ever have problems with rings on the sharp A/B port windows, did you just leave the as plated finish or was it dressed in some way.

You can sink the top (and bottom) edges of these ports, from zero at the corners to maybe 0,1 mm in the middle, depending on the port widths, while still maintaining sharp edges.
The sinking will spare the piston ring while the sharp top edges will hinder flow from the cylinder into the transfers.

[quote="Institute of TwoStrokes"]

Jan Thiel a écrit:

"Stucco Verde" works a treat and is a pleasure to work with as well.

Do you happen to have a technical specification sheet that came with the product? I think I've used it before, but under a different name. It was capable of 200°C, held up excellent and became even better when you put it in the oven right after applying it.

If the specifications are the same I can provide a link where it's cheaper (and comes in a bigger packaging unit)

Hi Frits, could you give a look at my new topic ( [Vous devez être inscrit et connecté pour voir ce lien] on "Technique"?

Haufen a écrit:

Do you happen to have a technical specification sheet that came with the product?

There it is: :)
[Vous devez être inscrit et connecté pour voir ce lien]

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

Vagelis a écrit:

Haufen a écrit:

Do you happen to have a technical specification sheet that came with the product?

There it is: :)
[Vous devez être inscrit et connecté pour voir ce lien]

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

seems to be different at first glance

page 13

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

We use this at our research center, it's almost indestructible when is cured...

cristogrr a écrit:

[Vous devez être inscrit et connecté pour voir ce lien]
We use this at our research center, it's almost indestructible when is cured...

Citation :

Temp resistance: - 40 °C to 120 °C (Max 180 °C for 0.5 hour)

...So I would not recommend modifying an exhaust duct with it.
The problem with higher-temperature filler materials is their prohibitive price. Any suggestions, Cristogrr?

Hi, anyone knows anything about the technique aprilia instead of 'crankshaft and countershaft?

t0nix a écrit:

Hi, anyone knows anything about the technique aprilia instead of 'crankshaft and countershaft?

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

Frits Overmars a écrit:

t0nix a écrit:

Hi, anyone knows anything about the technique aprilia instead of 'crankshaft and countershaft?

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

very thanks Frits, but i search the design technique