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

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 ???

Frits Overmars a écrit:

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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Hi,

Been doing some maths.
I have a rough RSA DAT2T file with give the same Angle.Area as Frits has posted. I scaled this up for the ports on a 80*80 B/S engine with port width % of bore and using the same timings

As expected there is less wall area as you increase cc of a cylinder so there is less Angle.Area (AA) from a scaled up port in the 400cc engine.

I got BD AA = 32735 deg mm^2 and Tx AA = 232467 deg mm^2

Working back from Frits's STA values I got a max torque RPM of 8756rpm for the BD AA and 8197 rpm for the Tx AA.

Frits, I think you said on KiwiBiker that AA is related to power? Can a predicted power out put be calculated like this?
BD : 400cc AA/ RSA AA = 32736/14543 = 2.25 2.25*59(RSA crank power) = 132.8 HP
TX: 400cc AA/ RSA AA = 232467/110315 = 2.1 2.1 * 59 = 123.9 HP


Bit of a rushed post, sorry but now 1 hr late for work!

Dave

rgvbaz a écrit:

Frits, I think you said on KiwiBiker that AA is related to power? Can a predicted power out put be calculated like this?
BD : 400cc AA/ RSA AA = 32736/14543 = 2.25 ; 2.25*59(RSA crank power) = 132.8 HP
TX: 400cc AA/ RSA AA = 232467/110315 = 2.1 ; 2.1 * 59 = 123.9 HP
Bit of a rushed post, sorry but now 1 hr late for work!
Dave

Give my love to your governor . Maybe it helps, Dave; you never know.
Angle.area is one of the factors determining how much combustible mixture per minute can be put through an engine. But the flow coefficient of the transfer ducts is just as important. The difference between a duct developed by Jan Thiel and an average duct can be as big as 20%. And I am not even talking about flat-squeezed transfer ducts in parallel twins with too-closely pitched cylinders. So much for power predictions....

Frits Overmars a écrit:

rgvbaz a écrit:

Frits, I think you said on KiwiBiker that AA is related to power? Can a predicted power out put be calculated like this?
BD : 400cc AA/ RSA AA = 32736/14543 = 2.25 ; 2.25*59(RSA crank power) = 132.8 HP
TX: 400cc AA/ RSA AA = 232467/110315 = 2.1 ; 2.1 * 59 = 123.9 HP
Bit of a rushed post, sorry but now 1 hr late for work!
Dave

Give my love to your governor . Maybe it helps, Dave; you never know....

....The difference between a duct developed by Jan Thiel and an average duct can be as big as 20%...

So much for power predictions....

Don't worry about the boss, Frits, I had a word with myself :-)

So if the ducts were as efficent as the RSA's ducts then the power prediction could be somewhere near.

Thanks again for your insights, Frits

Dave

Note: I got the Angle.Area's from Dat2T by taking the STA calculated by Dat2T and multiplying by 6*RPM (for calculation)*cc(swept volume)

Here is Electronic Fuel Injection at work in the " modern motorcycle"
Automotive injectors, fuel pump, filters, TPS unit, aftermarket computer ( Link Electro Systems )
All cheap off the shelf components. Works better than any carburator ever did on this motorcycle.
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And here entered in this years Acerbis four hour enduro. ( NZ )
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Well, we didn't come last and we did finish!

This is the flywheel trigger system, 12 - 1 , ie 11 pins and a gap. extra sensor is for the Ignitec ignition ( different trigger pin on the flywheel ). This was set up before the EFI ( and worked well ) so stayed in place, It also ran the vairable rotary valve so I didn't want to upset it [Vous devez être inscrit et connecté pour voir cette image]

This is the Lake Injector copy, this was used just as the throttle valve with EFI system. I used an "in cable" TPS with this slide throttle, not very accurite. Ball valve with TPS mounted straight to the throttle shaft is much better.
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Frits, would there be a rule (of thumb) for converting EGT values from different sensor locations?
Do you happen to have an EGT curve from the RSA? Judging from the pics, the probe was around 75mm from the piston face, eh?
(I guess you might be away, so it's ok if not. perhaps you remember the value at peak hp?)

Frits Overmars a écrit:

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.

You've understood correctly, below is a picture of my shoddy manifold. Based on what you've said and some of my conclusions I intend to run the injector(s) in the crankcase on the new engine. I had a lot of other problems with the 500cc engine that got in the way of optimizing the EFI to the extent that I had wanted in the time I had over the summer. Do you see any benefit to injecting in the transfers? All I see happening is a reduction in time for the fuel to mix with the air resulting in a lesser quality mixture. If I inject in the transfers I would also have to re-think my lubrication strategy. I want to separate fuel and oil via an oil injection system but I'm not ready to implement it at this time.

Also thanks for your comments on port timing. I have some more calculations to do!

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With my setup ( seen here earlier) injecting into the transfer port catchment, oiling seems not to be a problem. This setup has run more than fourty hours now ( racing and trail riding, would have seized by now if it was going to! ). Inspecting through the rotary valve indicates all insides are damp with oil. The injection is timed to start just after rotary valve has shut, it seems to me there is enough oil settling on the transfer walls and running down into the crank case ( big end ).
Injector "on time" ( fuel delivery ) happens from this point ( RV shut at high speed timing ) and at full throttle runs right up to near the end of transfer time. Approx 180 degrees injector"on time" each cycle. Each cycle starts fresh with no fuel left over from the last cycle. Accurite fueling! That parcel of fuel injected must be transfered to the combustion chamber every cycle cleanly. The closer toward the inlet, the less chance of a clean delivery every cycle, fuel will get mixed with the last delivery and every few cycles ( depending on crancase dynamics, airflow) the engine will switch lean to rich, feel flat and almost sound like a misfire but not. I'm trying to word this to make sense??? All I can say is with the switch from injecting at the beginning of indution ( RV opening ) to injecting when the transfers are about to open made a huge difference on the F9.
Engine runs 55 degrees low speed valve timing
78 degrees high speed
Engine will pull to 8600 but in MX will hit the 9000 rpm limiter somtimes.
Injectors are Bosch 700 x2
Fuel pressure is 45 psi
Fuel is E90
Computer is Link Atom ( fueling only )
Ignition is Ignitec

We are injecting a YZ250 shortly, the injectors are set up in the rear two transfers, I'll see if I can get some pictures of this setup if you like.

It is interesting that your engine didn't run as well with the injectors closer to the intake. I understand what you're saying but haven't experienced those problems myself. You probably know already but two similar strategies have been used with success on snowmobiles as well. Arctic Cat's snowmobiles were all injected before the reed similar to my engine and Rotax/Skidoo injected in the transfers for a few years the way you're doing. The main difference I see between yours and the Skidoo is that the Skidoo had an oil injection system. This led me to believe that without an oil injection system and just pre-mixing lubrication to the bottom end would be inadequate. I'm glad you've shared your findings as it potentially means I could try injecting in the transfers without worrying about lubricating the bottom end by other means.

Did you ever try any other injector sizes? I'm guessing you chose the big ones so that you could inject in the required 180 degrees?

Hi Everyone,

My name's Dan and I'm a two stroke fanatic from the UK. I'm currently working mainly on a Yamaha TZR 250 3XV SP.

Like many others here I have spent a long time reading through all of these interesting and informative posts. I'd like to say thank you to everyone who has contributed their experience, time and knowledge, it is a most fascinating read

Long may this thread continue.

Dan

On the injection models of the 350 Motobecane (4 prototypes only in 1974) the injector was placed in a specific transfert which have a différent timing (the top edge was identical to the 4 main ports, but the bottom edge was more high, because the port was only a small hole on the cylinder wall.
the oil was directly injected in the crankcase bearing, but also in the air intake, to protect the rear part of the piston.

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.

Mr PVO,

The designing of a cylinder from scratch had me a little out of my depth. So I am getting a price from an experienced friend to do the 3D modelling and rapid sinter casting of an 80x80mm cylinder. He has designed a 50cc world championship cylinder so hes certainly more qualitifed than I.
It will be as close to an RSA cylinder as possible, so if you'd like to jump on this bandwagon I can ask about getting another one made for you? send me a PM or reply with your email if your interested.

bentou a écrit:

On the injection models of the 350 Motobecane (4 prototypes only in 1974) the injector was placed in a specific transfert which have a différent timing (the top edge was identical to the 4 main ports, but the bottom edge was more high, because the port was only a small hole on the cylinder wall.
the oil was directly injected in the crankcase bearing, but also in the air intake, to protect the rear part of the piston.

Hello bentou
Do you know more about the Motobecane engine? In a german book is written that it has worked very well.
Thankyou.

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PVO a écrit:

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

Pretty hard unfortunately. The C code was clearly written by someone without a lot of C experience, it's basically assembler translated into a higher level language without any real structure... then features were cobbled on one by one. Which is why I decided to start again.

Second, it's real time C, ie interrupt driven. That was a new experience for me and caused a lot of stress. Plus the fact that a microsquirt isn't by default connected to any sort of output device... I was debugging by listening to when and how it clicked the fuel pump relay!

Third, the compiler provided by Freescale (the chip manufacturer) is a disgrace: very poorly documented and lots of things simply don't work. For example if you want to add 2 numbers and divide the result, in C it's legitimate
to write
x=(a+b)/4;
but that would generate an incorrect answer, it needed to be split into 2 separate commands.

Plus of course there is no floating point, everything needs to be written in integers, and even the handling of negative numbers doesn't work as it should! Probably why they give it away for free.

I finally proposed to a friend we should publish a book:
"A new paradigm for coding: push-it-home error detection"

In fact I never had to push it home, but it was pretty damn close one night...

I'm happy to hand over my code to anyone who wants to play with it. The microsquirt forum deleted my posts as soon as I said I wasn't using the standard software

PS I should say that most of the logic of the code was not that difficult if you know a bit of physics. The compensation for partial transfer of charge was dramatically simplified in my version and in any case turned out to be almost irrelevant.

The most difficult parts were
a) writing the logic to sync with the flywheel pulses;
b) getting the auto-tune to work when the compiler didn't want to know about negative numbers;
c) handling the routine for rewriting new fuel tables into the non-volatile memory, which needs to be coded at the assembler
level (take number in memory location X and add it to that in memory location Y), thanks to some incorrect sample code.

PVO, to be fair, my injectors are crank case, just in the transfer catchment and like I said I'm not trying to tell anyone how to suck eggs! Just point out what I've found.
My injectors were placed where they are due to having to keep them out of sight ( classic racing ) as it's ended up this is exactly the right place to fit them for this engine. All wires run through original vacume and oil rubber hoses. This bike is well known for running a Lake Injector, I've just taken it one step further.
This is the head I use, plenty of fuel air movement ( mixing ). Copy cast from original head.
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