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

Howard Gifford a écrit:: I had an idea. What if there was a tube connected to the pipe and on this pipe was a reedvalve that allowed fresh mixture into the pipe. It would be connected to a tube to the carburettor before the reedvalve or rotary valve. It would bypass the transfer port/ crankcase route to allow fresh charge to be directly put into the pipe during the scavenge cycle. Then it would be available to put back into the cylinder.

Why would you want to bypass the crankcase Howard? All crankshaft bearings would be starved of lubrication and cooling, and the piston crown would dearly miss cooling by the incoming mixture as well. True, your mixture would be a bit cooler than it is now, but if you don't remove the heat from bearings and piston, the engine won't live very long.
The mixture would also be less homogeneous because it would not be stirred by the crankshaft.
Then there is the problem of starting it. If you have no crankcase pumping, how will you ever get sufficient mixture in the cylinder for combustion?

Nombre de messages : 8 Localisation : USA Date d'inscription : 11/02/2011

Would this be in addition to the normal induction system? To increase the amount of mixture available to stuff back into the cylinder?

Yes it would be an additional path to get more charge into the header of the pipe. the carburettor would still pass most of the inlet charge through the crankcase in the normal fashion. Lets say a 19 mm diameter tube and a steel petal reed valve mounted close to the exhaust pipe. It would be connected to the carb boot similar to the way a boost bottle is connected

Howard Gifford a écrit:: Yes it would be an additional path to get more charge into the header of the pipe. the carburettor would still pass most of the inlet charge through the crankcase in the normal fashion. Lets say a 19 mm diameter tube and a steel petal reed valve mounted close to the exhaust pipe. It would be connected to the carb boot similar to the way a boost bottle is connected.

That could work, Howard. But an exhaust pipe can only create so much suction. Creating a 'leak' between pipe and cylinder would reduce the mass of mixture flowing through the cylinder during scavenging, so scavenging and piston cooling would suffer. But yours is a simple setup, so why not build it and let us know how it goes?

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

Sanderhoutman a écrit:: Manuel,

Just make verry clear how you want it done and let them confirm that they agree.

You might want to contact emot first he has iff i recall correctly a spanish company doing it also and that is much closer to home.

Maybe try it with a less important cillinder first.

thanks for the informations Sanderhoutman and koenich

Manuel

Nombre de messages : 56 Localisation : Austria Date d'inscription : 02/03/2014

Hi everyone,
Somewhere Frits wrote that it would be ideal to have a duct change direction in only 1 plane.
I have tried to apply this theory, and combined it with an rsa-like port layout.
Here are some pictures:

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As you see the leading, and trailing directional angles are the same as on the start of the duct (on the underside of the cylinder) so that the duct makes the gasses travel in that direction as soon as possible, making as little bends as possible. I used the directional angles you gave us in your 'leaning tower theory'.

It is not finished yet, but do you think it would have any chance at beating/outperforming a traditional duct?
Thanks you for your time and sharing your knowledge!

It's looking really nice, Senne. But it will be extremely difficult to improve on the traditional ducts that were developed by Jan Thiel.
By the way, instead of looking at the scavenging angles in my Pisa-story, look at the FOS scavenging concept I posted not too long ago. Those angles are more up-to-date.

Nombre de messages : 56 Localisation : Austria Date d'inscription : 02/03/2014

Thanks a lot frits!

Nombre de messages : 20 Localisation : Allemagne Date d'inscription : 22/05/2013

Frits Overmars a écrit:: By the way, instead of looking at the scavenging angles in my Pisa-story, look at the FOS scavenging concept I posted not too long ago. Those angles are more up-to-date.

Hi Frits,
I have red everything in these for topics and want to thank Jan and you for everything. You guys are awesome!

Comparing the FOS 50ccm concept, the RSW drawings that were posted here, and an Rotax129 Cylinder, a question accured to me.

On the Rotax129 the exhaust-side of the A port is aiming straight at the Boostport. The RSW is aiming only few millimeters from the centre of the cylinder (boostport side), and then the FOS cylinder is pointing circa at the midpoint between boostport and cylinder-centre.

I allready know, that the aiming depends a lot on the desired RPM range of the engine, but i wonder:
Was this a development step back, because it did not work as hoped on that RSW cylinder? Or is the RPM range the answer?

Thanks
Tim

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

Tim Ey a écrit:: On the Rotax129 the exhaust-side of the A port is aiming straight at the Boostport. The RSW is aiming only few millimeters from the centre of the cylinder (boostport side), and then the FOS cylinder is pointing circa at the midpoint between boostport and cylinder-centre.

Thanks
Tim

thats basically the same question i asked on the previous page. i arrived at the same conclusion you did. to me the rsw A port exh side appears to be aimed about the center of bore while the 50cc concept A port exh side appears to aim about 3/4 to the rear of cylinder

maybe the rsw drawing only represents the entrance of the A port exh side and perhaps theres some sort of radius turn in the tunell near the window exit that aims it much farther to the rear of cylinder than what the drawings show ?

brokedown a écrit:

Tim Ey a écrit:: On the Rotax129 the exhaust-side of the A port is aiming straight at the Boostport. The RSW is aiming only few millimeters from the centre of the cylinder (boostport side), and then the FOS cylinder is pointing circa at the midpoint between boostport and cylinder-centre.

Thanks
Tim

thats basically the same question i asked on the previous page. i arrived at the same conclusion you did. to me the rsw A port exh side appears to be aimed about the center of bore while the 50cc concept A port exh side appears to aim about 3/4 to the rear of cylinder

maybe the rsw drawing only represents the entrance of the A port exh side and perhaps theres some sort of radius turn in the tunell near the window exit that aims it much farther to the rear of cylinder than what the drawings show ?

Yes, that is indeed the case!
There is a very big twist in the transfer tunnel.
The exhaust side of the A-transfer was directed as much away from the exhaust as possible!

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

thnx for clarifying that jan. i suspected there was some twist in the tunel near the window exit but i wasnt 100% sure because the drawings dont seem to show it

brokedown a écrit:: thnx for clarifying that jan. i suspected there was some twist in the tunel near the window exit but i wasnt 100% sure because the drawings dont seem to show it

There has been a cylinder scan on this forum, some time ago, that clearly shows it!
I also have good photos of the transfer cores, but do'nt know how to put them here, sorry!

Jan Thiel a écrit:: There has been a cylinder scan on this forum, some time ago, that clearly shows it!
I also have good photos of the transfer cores, but do'nt know how to put them here, sorry!

If those are the pictures I sent you last year, just give me the names of the pictures. I can post them here, Jan.

Frits Overmars a écrit:

Jan Thiel a écrit:: There has been a cylinder scan on this forum, some time ago, that clearly shows it!
I also have good photos of the transfer cores, but do'nt know how to put them here, sorry!

I guess those are the pictures I sent you last year. If you give me the names of the pictures, I can post them here, Jan.

Yes I would like that Frits!
Do you have the pictures of the sand cores of the RSA?
I will put them on FB!

Jan Thiel a écrit:

Frits Overmars a écrit:

Jan Thiel a écrit:: There has been a cylinder scan on this forum, some time ago, that clearly shows it! I also have good photos of the transfer cores, but do'nt know how to put them here, sorry!

If those are the pictures I sent you last year, just give me the names of the pictures. I can post them here, Jan.

Yes I would like that Frits! Do you have the pictures of the sand cores of the RSA? I will put them on FB!

You mean these?

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Nombre de messages : 57 Localisation : DFW,Texas Date d'inscription : 15/11/2013

That's some FINE VooDoo !!!! Beautiful !!!!

Frits Overmars a écrit:

Jan Thiel a écrit:

Frits Overmars a écrit:

Jan Thiel a écrit:: There has been a cylinder scan on this forum, some time ago, that clearly shows it! I also have good photos of the transfer cores, but do'nt know how to put them here, sorry!

If those are the pictures I sent you last year, just give me the names of the pictures. I can post them here, Jan.

Yes I would like that Frits! Do you have the pictures of the sand cores of the RSA? I will put them on FB!

You mean these?

Yes Frits, thanks!

No 'hooks' or 'kickers' as you can see!
Everything was done to promote good flow.

Nombre de messages : 151 Localisation : usa Date d'inscription : 29/09/2013

thnx jan and frits wanted - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 15 771973

. the mold pictures removes all the mystery for us unfortunate people that havent had the pleasure to see the rsw or rsa cylinders first hand

Nombre de messages : 56 Localisation : Austria Date d'inscription : 02/03/2014

I am trying to rescale an Rsa portlayout to 50cc size, now the bridges between the transfers get as narrow as .9mm. Would this be reliable enough for a 50cc racing cylinder?

Senne s a écrit:: I am trying to rescale an Rsa portlayout to 50cc size, now the bridges between the transfers get as narrow as .9mm. Would this be reliable enough for a 50cc racing cylinder?

Yes, I think so!

Great pics!!!

Thanks so much Jan!!! (and Frits)

wanted - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4) - Page 15 771973

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Hi Jan,
Thank you for sharing your knowledge over these years - I appreciate it very much.

You mentioned previously about the auxiliary exhaust port dividing wall :

“I tried to keep them separated by making the 'dividing wall' longer.
I did this mainly to keep it from cracking!
It resulted in power loss and a lot less max. revs
So I had to make the 'dividing wall' as short as possible.”

Do you know now what caused this power loss?
Do you think this would also be the same for a bridged exhaust port like the Honda?

Regards
Allan.

GtG001 a écrit:: Hi Jan,
Thank you for sharing your knowledge over these years - I appreciate it very much.

You mentioned previously about the auxiliary exhaust port dividing wall :

“I tried to keep them separated by making the 'dividing wall' longer.
I did this mainly to keep it from cracking!
It resulted in power loss and a lot less max. revs
So I had to make the 'dividing wall' as short as possible.”

Do you know now what caused this power loss?
Do you think this would also be the same for a bridged exhaust port like the Honda?

Regards
Allan.

No, I still do'nt know why, I tried a lot, but did not succeed!
With bridged ports I have a very limited experience.
I hate them!

Thanks Jan for your reply,
The loss of max revs might indicate that it pulled more charge out of Transfer A by being longer and cooled the pipe too much?
Maybe, the longer wall reduced turbulence and thereby increased the suction of the exhaust wave?

Regards
Allan.

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