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

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This is the "ball" throttle valve with TPS. Runs on bearings.

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These are the injectors ( 2x ) in the rear port catchment
Bike is 1973 modle

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Valve housing mounted on the Kawasaki F9.
You can see the injectors mounted in the air duct behind the cylinder.

Hi Uniflow,
Thanks for the interesting and very clever development pieces. Can we see more of your work.

If I remember correctly, the Kawasaki F9 was called a BIGHORN –It is an appropriate name for your trail bike now!
That was a golden era when most of the 2 stroke bike manufacturers had a large displacement Trail or Motocross bike in the 350-500cc range.
My favourite was the 500cc Maico – that was awesome to watch when it came on power and the sound was pure music for the 2 stroke fan.

Frits, you have seen this housing before? From Wobbly? I don't want to push in on your forum, I'm just interested to see who else is playing with EFI and vairable rotary valves. My next valve housing will be a little different again. Tuning this Link EFI system has been a long process, much of it with my laptop computer zippy tied to the fuel tank. Not too good for the computer!! There have been may issues to solve but it runs quite well now.

GtG001, yes those were the days. I had one of these Bighorns with a hot kit when I was 16, it left it's mark on me both physically and mentally, It was quite explosive. I can't see why we shouldn't return to those days again with EFI being able to help clean the twostroke up. I think the right place to put the injectors is in or on top of the transfer ports. With a little control, fuel need not be flushed out the exhaust port.

uniflow a écrit:

Frits, you have seen this housing before? From Wobbly? I don't want to push in on your forum, I'm just interested to see who else is playing with EFI and vairable rotary valves. My next valve housing will be a little different again. Tuning this Link EFI system has been a long process, much of it with my laptop computer zippy tied to the fuel tank. Not too good for the computer!! There have been may issues to solve but it runs quite well now.

I feel your pain, I've got a KX500 engine running on EFI using a Microsquirt ECU and various components. Can you incorporate a power valve or oil pump map with the link ECU?

I have a microsquirt running my, ahem, 4-stroke. However the interest is that I found the microsquirt code so horrible that I rewrote the whole thing from scratch to be a proper TPS + rpm based system, rather than the standard hack one is required to do if one doesn't want to use manifold vacuum as the principal parameter.
I also include a more intelligent lambda-based auto-tune and it tunes itself quite quickly.

Does anyone know if it is feasible to use a lambda to tune a 2-stroke, despite the oil contamination issues? Obviously you wouldn't want to run it permanently, only long enough to get a working map.

The other obvious question: given that intake volume on a 2 stroke is so dependent on the pipe, which depends on the pipe temperature which depends on the recent history (ie throttle position and rpm for the previous 10s or so), how precise can one be with EFI?

uniflow a écrit:

Frits, you have seen this housing before? From Wobbly? I don't want to push in on your forum, I'm just interested to see who else is playing with EFI and vairable rotary valves.

I can't remember where I saw it, but in any case it was on a forum where Wobbly contributes. So yes, he is probably guilty (unless you yourself posted it on [Vous devez être inscrit et connecté pour voir ce lien] ).
And don't worry about pushing in; you're very welcome.

GrahamB a écrit:

Does anyone know if it is feasible to use a lambda to tune a 2-stroke, despite the oil contamination issues? Obviously you wouldn't want to run it permanently, only long enough to get a working map.

It's quite feasible, Graham. Two things to observe: don't put the probe too close to the cylinder or it will get oiled up with washed-through mixture; somewhere in the belly is fine. And make sure the probe is heated up to its working temperature before you start the engine. That way it will have a chance to burn off any oil that gets to it.

Citation :

The other obvious question: given that intake volume on a 2 stroke is so dependent on the pipe, which depends on the pipe temperature which depends on the recent history (ie throttle position and rpm for the previous 10s or so), how precise can one be with EFI?

I can't be specific, but it will certainly beat a carburettor.

Neil, I was wondering. If you have this: [Vous devez être inscrit et connecté pour voir cette image]
Then why also have this? [Vous devez être inscrit et connecté pour voir cette image]
Wouldn't it be possible to move that disk timing controller to the completely shut-position and have it double as a throttle valve? It would require a bit more programming but you would have ride-by-wire and simpler mechanics.

uniflow a écrit:

Frits, you have seen this housing before? From Wobbly? I don't want to push in on your forum, I'm just interested to see who else is playing with EFI and vairable rotary valves. My next valve housing will be a little different again. Tuning this Link EFI system has been a long process, much of it with my laptop computer zippy tied to the fuel tank. Not too good for the computer!! There have been may issues to solve but it runs quite well now.

Howard Gifford , aka flatout on this forum has developed a variable rotary valve system on his champ 440 Rotax snowmobile engine.. The twin cylinder race engine with bore 65 mm. stroke 65.8 mm was converted from cylinder reed to rotary valve with a sliding inner cover that varies the closing timing by 30 degrees to allow the engine to start with milder timing and after starting and coming off the pilot jets the timing closes later for best peak power... It works superb...

GrahamB a écrit:

I have a microsquirt running my, ahem, 4-stroke. However the interest is that I found the microsquirt code so horrible that I rewrote the whole thing from scratch to be a proper TPS + rpm based system, rather than the standard hack one is required to do if one doesn't want to use manifold vacuum as the principal parameter.
I also include a more intelligent lambda-based auto-tune and it tunes itself quite quickly.

Does anyone know if it is feasible to use a lambda to tune a 2-stroke, despite the oil contamination issues? Obviously you wouldn't want to run it permanently, only long enough to get a working map.

The other obvious question: given that intake volume on a 2 stroke is so dependent on the pipe, which depends on the pipe temperature which depends on the recent history (ie throttle position and rpm for the previous 10s or so), how precise can one be with EFI?

I too have found that using the lambda sensor on a two-stroke has been a non issue. I've found it to work well enough that once I've established an initial map I can run closed loop primarily based on the lambda sensor readings.

Graham, how difficult would it be to re-write the code for someone that doesn't have a lot of programming experience?

Frits, while Jeram and I design our 400cc cylinders I am wondering how the port timing scales? I understand how variables like length scale but how to determine the correct timing is a little less clear to me. I think I read in one of your posts that no matter what type of tune (road race, motocross, etc) you are going for the theoretical exhaust port open time should be 192 degrees. Is this a good place for me to start or is there a better way to determine this? And what about the transfer ports? I would image they should have less timing to some degree too while maintaining their staggered relationship. My reasoning for less time would be that since the max power RPM (8850) is less than 13,500 the area required to get the required air into the cylinder would be less. Thanks for any insight.

Hello everyone,


My name is Matt, I am an electrical engineer from Florida USA. I just wanted to say thank you to Mr Jan Thiel and Mr Frits Overmars for sharing so much with all of us.

I am a huge two stroke fan and simply cannot believe how incredible and open and sharing everyone is on this forum. I am so happy to see this, and cannot say thanks enough to everyone on this forum for sharing everything.

So much more makes sense, so many more questions have been answered now.

Thank you again.

Frits, yes the new engine valve case will be run as the throttle as well ( no ball valve required). The Link computer can handle this operation. This idea came to me after the F9 valve housing was run successfuly. Will make the engine a little thinner Too.

PVO a écrit:

Frits, while Jeram and I design our 400cc cylinders I am wondering how the port timing scales? I understand how variables like length scale but how to determine the correct timing is a little less clear to me. I think I read in one of your posts that no matter what type of tune (road race, motocross, etc) you are going for the theoretical exhaust port open time should be 192 degrees. Is this a good place for me to start or is there a better way to determine this? And what about the transfer ports? I would image they should have less timing to some degree too while maintaining their staggered relationship. My reasoning for less time would be that since the max power RPM (8850) is less than 13,500 the area required to get the required air into the cylinder would be less. Thanks for any insight.

Assuming we are talking about competition engines, I would say that 190° for all exhaust ports and 130° for all transfers (so no staggering) is ideal.
The total angle.area of the transfers divided by the total scavenged volume per cylinder (cubic capacity plus combustion volume) determines at which rpm the engine starts running out of breath. Revving it much higher does not make much sense.

The picture below shows the Aprilia RSA125's blowdown angle.area and transfer angle.area. If you divide these values by the 124,8 cc cubic capacity plus the 8,6 cc combustion volume, and by the 12.500 rpm at which this engines develops its maximum torque, you will find the optimum specific time.areas for blowdown (8,72°mm² per cc per 1000 rpm) and transfer (66,16°mm² per cc per 1000 rpm) .
Your engine should meet these same specific time.area values, so if you know its angle.areas, its cubic capacity and its combustion volume, you can calculate the rpm of maximum torque.
It may be necessary to raise the exhaust timing beyond 190° in order to get the required blowdown angle.area for the rpm determined by the transfers (that is the reason for the RSA's 202° exhaust timing).
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mattology a écrit:

Hello everyone, My name is Matt, I am an electrical engineer from Florida USA. I just wanted to say thank you to Mr Jan Thiel and Mr Frits Overmars for sharing so much with all of us.
I am a huge two stroke fan and simply cannot believe how incredible and open and sharing everyone is on this forum. I am so happy to see this, and cannot say thanks enough to everyone on this forum for sharing everything. So much more makes sense, so many more questions have been answered now.
Thank you again.

Thank you for your kind words, Matt.

PVO, yes the Link is a versatile unit. Are you running your injectors into the throttle body?

uniflow a écrit:

PVO, yes the Link is a versatile unit. Are you running your injectors into the throttle body?

No, I'm running it into a specially made intake manifold. I inject a little before the read valve. I will try to find a photo of it when I have time.

PVO a écrit:

I inject a little before the read valve.

If I understand correctly, you inject upstream of the reed valve. Modify that if you can; I have taken Strobotak (see Wikipedia) views of fuel/air-mixture where the fine fuel droplets hit the reed, merge, and subsequently flow off the reed as much larger drops. Injecting downstream of the reed will also minimize fuel blowback.

What I'm relaying here is just my own conclusions, not saying anyone else is wrong.
I had a lot of trouble getting my F9 to run clean up to about 1/3 throttle and part of this problem was the default settings in the Link computer, accelerator pump etc. There are two ways the injectors can be fired with this system, timed or batch fire ( squirt ). It seems the batch squirt system is random in reguards to when the injectors fire against timing. As in when the engine starts it will find a possition to squirt and stay there. Next time you run the engine it will find a different possition to squirt. Ok for a four cylinder car engine but no good for the F9 single. Found that problem changed to timed injection. I decided to inject as the rotary valve opened, fair assumsion? It would run but but felt flat down in the revs, didn't matter if it was rich or lean, ignition time advance or retard, same result??
By accident I changed the injection timing to start injecting just before the transfer port opened. The "monster" had returned!! Forget carburators they flow air / fuel at a constant mixture rate, injection is pulesd so at low speed you will end up with a "parcel" of fuel over a short induction then only air after that( each induction). With the dynamics of the crankcase you can not guarantee that this "parcel" of fuel will end up in the combustion chamber every cycle and that is what was happening. This is why I imagine a small injector is used at low speed to mix fuel over a long induction period to try and get a better mix. Injecting at the transfer port works well, more to come.

Jan Thiel a écrit:

michaelten a écrit:

Jan,

I have been looking for information about using unleaded fuel.

Information I am finding is saying that using unleaded the size of the silencer is important.

What did you find about silencer sizes when developing the RSA?

Thank you

Michael

We used the same silencers as before with unleaded fuel.
Only the 'restrictor' size went up by 0,25mm

Hi Jan, I'm interested with the pre unleaded era, would you and Frits share with us some of you views and or opinions with the use of Avgas as a fuel if it was to be used in a RSW or RSA.
Such as the smaller stinger diameter, your views with regards to combustion chamber shape, ignition timing, cooling system differences, pipes, egt's,

Ken Seeber a écrit:

Allow me to introduce myself. My name is Ken Seeber and I live in Perth, Western Australia. I have been interested in 2 stroke engines and motorcycle GP technology since forever. I was fortunate to work at the Orbital Engine Company for 25 years where a lot of time was spent on the design and manufacture and/or application of various 2 stroke engines, the key focus of this activity was the application of the Orbital 2 fluid direct fuel injection system. This offered many gains in terms of fuel consumption and emission reductions with production applications on various 2 stroke engines including Mercury Optimax outboards, Piaggio, Aprilia and other 50 cc scooters.
During this time, I built and raced a 125 cc bike, based on an early YZ125 (Ø56 * 50) engine which I converted to watercooling with a rotary disc valve using a magnesium 34 mm Mikuni as used on an RG500 engine.

Being a late/recent starter in getting on to the Pit-Lane 125 Aprilia forum, I got excited after reading Frits’s articles on transfer ports, particularly in Page 33 where he suggests the axisymmetric layout with all the transfer ports pointed radially inwards.
We built a cylinder of this type in around 1984, even using hydroformed pipes. The pictures tell the story. Perhaps a bit crude with handmade patterns, welded on water jacket etc, but as a homebuilt project, it was the only way at the time. How did it go? Not as good as the modified YZ cylinder, but in hindsight the port timings were far too mild. However, as a result, it idled extremely smoothly (reliably 2 stroking) indicating good cyclic stability of the scavenging process. If I did another one I would incorporate a downslope roof for the exhaust ports, upslope for the roof of the transfer ports plus more current (eg Aprilia RSA 125) port timings with exhausts to suit.

Didn’t go any further with it at the time due to wives, kids, house, career etc. However I do believe that Frits is absolutely correct in pointing to this layout offering a step increase in performance.
There are some downsides to such an engine layout:
1. Exhaust system. I obviously used 2 separate pipes, and this maybe the best for overall performance, although a single pipe system is possible, but for the fact that one may experience too much cooling of the exhaust gases if they were ducted into one outlet within a cast cylinder resulting in a loss of exhaust energy. Either way, packaging could become an issue, possibly practically limiting it to a one cylinder application.
2. Exhaust &fuel/air mixture gases short circuiting between exhaust and transfer ports. To minimise this, it would be necessary to provide a piston profile that is close fitting, particularly directly below the ring. However, this not to say that this is not important in any high performance 2 stroke engine with a close proximity or overlap between the exhaust and transfer ports.
3. Piston cooling. Approx 70% of the heat transferred to the piston is conducted away to the cylinder bore via the piston ring(s). The main moment for this to occur within the cycle is at TDC and BDC when the piston stops and provides the greatest time for the transfer. This is well recognised in most current performance 2 strokes by the fact that the coolant is introduced behind the cylinder wall under the exhaust port, at a level where the ring stops at BDC. However, when we surround the cylinder with transfer ports/passages, this is basically no longer easily possible.

We are still involved in 2 stroke engines with a business in Perth manufacturing pistons for Yamaha kart engines ( [Vous devez être inscrit et connecté pour voir ce lien] ).

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Hi Ken, nice post, As you were involved with the Orbital company and it producing various 2stroke items namely it's fuel injection ideas as well as yourself being a 2stroke racer, perhaps you would share with us all some history upon the Orbital injection story and you views upon how a 2stroke enthusiast may go about implementing an injection system in this modern era

What ever happend to the development of the Carbon / Carbon pistons that were going to be the next big thing ???