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

love the sliding plate idea,
you have done exactly what i find hard words to explain, well done ,
perhaps later, for better power distibution, a servo moter and programable ignition/valve system ?
nice work,
(can we see the rest of the engine please ?)
david

Howard,

Congratulations! Good job.
Does it work correctly? What is the result on the dyno. Is that the shape of the curve has improved?

Dyno testing confirmed that the engine makes more power with 105 degree closing. I gained 4.5hp over 80 degree closing. I also was able to hold the torque at higher revs. Most dyno runs are done with a sweep test at full throttle so the variable timing is more of a starting aid. We use a cvt on our snowmobiles and our rpm is pretty constant at 10500. Even with electric start the engine will not start with timing over 100 degrees closing.

Howard Gifford a écrit:

Dyno testing confirmed that the engine makes more power with 105 degree closing. I gained 4.5hp over 80 degree closing. I also was able to hold the torque at higher revs. Most dyno runs are done with a sweep test at full throttle so the variable timing is more of a starting aid. We use a cvt on our snowmobiles and our rpm is pretty constant at 10500. Even with electric start the engine will not start with timing over 100 degrees closing.

Your work is awesome!
I have been waiting for someone to utilize such an idea!you must be a...pioneer in this
field.
I m sure in the future with more variables input you will achive even more,you have also done away
with the complexity of something like the ''scissor disc" idea.
keep it up thank you for posting.

@ fpayart,
Francis, est que cette systme est utile dans tes moters ou pas le peine a cause de la besoins de les superkarts

David,

Nous avons dessiné il y a au moins 5 ans déjà, un sytème similaire mais avec une variation de la valeur d'avance à l'ouverture et ègalement une variation du retard à la fermeture.
Malheureusement les journées sont trop courtes et le projet est resté à l'état de projet

I am interested to hear what Frits and Jan think of this idea and if they have any suggestions as to what their ideas about variable inlet timing are? I remember reading a post by Jan Thiel stating they were planning such a design for the RSA125 but it never was completed.

I am also working on developing a rotary valve engine with a much larger diameter disc (190mm vs 126mm). I should mention that the engine is a twin cylinder 440cc Rotax with transverse rotary valve shaft that uses one disc to control both inlet ports. Our rules restrict us to VM34 Mikuni round slide carbs. I am targeting 135HP@ 10600 with this engine. So far the best we have achieved with ourr current setup is 128HP at 10500 rpm.
My thought is to make very wide oval shaped (65mm) but not very tall (34 mm) inlet ports. This way I can open and close the port in much fewer crankshaft degrees yet maintain a large port area. I can also centralize the port on the centerline of the crankshaft. The centre lines of the rods are 130mm apart. My thought here is to achieve symetrical flow to both sets of transfers for better scavenging and even distribution of transfer flow. One of the problems with this design is that the port opens on the top on one cylinder an on the bottom of the port on the other.

Another question is the use of a "Boost bottle on a rotary valve engine that effectively connects both inlet ports to each other. My thought is that since we are restricted to 34mm carbs, in order to get more airflow through the motor we need more carb area. A boost bottle would allow each cylinder to draw from both carbs which in my theory will allow more airflow through the motor.
Maybe I am asking too many questions.

Howard, the subject of variable rotary inlet timing deserves more time than I can make available right now. But at least now I understand where your incredibly late disk closing timing stems from: from the ridiculously small carburetters you are obliged to use. Your engine deserves to have 48 mm carbs, so with the 34s a boost bottle would do a lot of good.
But I think you can do even better: forget the boost bottle and make a 34 mm cross-connnection between both inlet tracts. Then each crankcase can inhale through both carbs.
And make the inlet tracts as short as possible; that also helps.
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Thank you Frits for your insight. Yes it would be nice to run big carbs but the race associatiopn is trying to keep our speed in check with carb size however we are always looking for ways around the rules. The rule forbids modifications that allow a cylinder to draw air from more than one caburettor unless the engine was equipped with the device as manufactured. \There is also a rule that allows converting from reed to rotary or vice versa. The rotax reed motor came from the factory with a boost bottle so i decided to convert the reed motor to rotary and thus I can use the boost bottle on the rotary.

What do you think of my idea of a large diameter plate to quicken the opening and closing of the plate? Does having a symetrical inlet help to evenly distribute the transfer charge?

No one has commented on my pipe fabrication yet. I feel that hydroforming is superior to sectioned pipes in that the pipe has no sharp edges to breakup the wave. I have developed a method of hydrofoerming that allows me to hold a very tight tolerences and manufacture repeatable results. Any comments weather good or bad are appreciated coming from someone with your experience.
||Thanks Howard...

If a hydroformed exhaust gives a better performance then I would have expected a bike like the RSA125 to have it.

personaly i feel that the gas needs the angles to "tell" them what to with precision,
perhaps its better to have the header hydroformed

persenalement je sens que les gaz besoin des arrettes bien difinie pour leur dire avec plus de precision,
peutre cest mieux a le dubut de pot (header) avec le fabrication hydroformé

Frits Overmars a écrit:

You want transducers, Lawrence? Here you go:
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But this is not a picture from the Derbi racing department....

Hello everyone!

That dyno looks familiar. Here is a picture of it when my test engine was on there in 2002.
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My name is Brian Callahan. I graduated from Queen's University Belfast in 2004. I studied in the Internal Combustion Engines Research Group under Robert Kee. Robert Kenny and Robert Fleck were my co-advisors. Robert Fleck was the manager of the QUB-Optimum GP250 team at the time. I think the testing shown by Frits above is Bryan Fleck's work. Bryan is Robert's son and a good friend of mine. Bryan graduated with his PhD one year after me and now works for Hendrick Motorsports in NASCAR.

I work on 2-stroke diesel engines. The company I work for is developing new medium-duty and heavy-duty highway truck engines. I work mostly on piston rings, skirts, liners, and honing but my real joy is tuned pipes and port design.

For fun I race R/C 2-stroke boats. I was especially interested in Frits' 6.6 cm³ engine a few pages back. Amazing. I'm glad to see someone finally made some proper "teacup handle" ports for an R/C engine. I run 11 cm³ with 60% nitromethane in hydroplane boats. Together with my friends we work on 3.5 cm³, 7.5 cm³ and 15 cm³ engines also.

I have huge respect for the GP125 engines. I think they are the most impressive 2-strokes around. 430 hp/L on gasoline!

This forum, and this thread in particular, seem the best on the internet for high-performance 2-strokes. There are some very high caliber folks posting here. I am enjoying reading every bit.

Please forgive me for not knowing how to read or write in French. I am making prodigious use of babelfish.com to understand what everyone is saying.

Hi Brian, glad to have you here .

Brian student of QUB !

Welcome on board, Brian!

Pit-Lane.biz a les chevilles qui enflent en lisant Brian! Je suis ne suis qu'un amateur éclairé et je me dis souvent ce que dit dit Brian en lisant ces grands pros ici!

The Brian words make Pit-Lane.biz as a big-headed folk. I am an amateur and I often think what Brian said about these high level pros!

Frits or Jan, what was the highest peak cylinder pressure for the RSA125? Also, what sort of trapping pressure went along with that? This is interesting to me because my job involves turbocharged 2-strokes where we balance boost, peak pressure, and fuel efficiency.

Also, were there any friction measurements? I am keen to know what sort of FMEP the GP125 engines developed.

Development of the Aprilia two-strokes stopped in 2008 and my access to the data you ask for is limited at the moment so I will have to do my answering from memory. Trapping pressure was 2 bar abs and peak cylinder pressure was 65 bar abs. There have been friction measurements but I have no data on those.
Maximum torque of the RSA125 was 29.5 Nm between 12,000 and 12,500 rpm, measured at the secundary gearbox shaft. That should give a BMEP of about 17 bar
(show me a naturally-aspirated four-stroke that matches this value, Formula 1 included ).
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Hi Frits

If we use a 5% transmision loss on the RSA we get 31nm ( and 56,5hp ) this gives a BMEP of 15,6 bar.

A 2006 F1 V8 was around 15,18 bar ( 290nm )

But of course it's very hard to compete against an engine which only needs one crank revolution to give a full cycle.

Interestingly a 2006 Nascar 8V engine produced around 706nm from 5,86L giving a BMEP of 15,13bar.

I'm not an engineer, and i've a huge lack of kowledge, especially about 2 stroke engines.

Would you please explain me what is BMEP and what is a "standart value" about this ?

I mean, when you say a 15.16bar BMEP, is that good ? what is the value for a standart stock engine as we can get on out road bikes (a L4 600cc 4 stroke one as an exemple)

Brake Mean Effective Pressure

The definition of BMEP is: the average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.

A 2012 Yamaha R6 has a BMEP of 13,8bar.

A Ferrari 458 Italia 15,1bar.

Frits

I found this one:

Formula 3 engine from VW.

1997ccm and 250nm giving 15,73bar.
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They run low rpm's because of the small restrictor and this gives an impressive torque on a 2L engine.

4 stroke isn't that bad:-)

Mic a écrit:

If we use a 5% transmision loss on the RSA we get 31nm ( and 56,5hp ) this gives a BMEP of 15,6 bar.

Transmission losses are in the region of 5% per transmission step. From the crankshaft to the primary gearbox shaft you loose 5% of the crankshaft power. In the gearbox you loose another 5% of the input. So the 54 hp measured at the secondary gearbox shaft, was 95%*95% of crankshaft hp; crankshaft hp was thus 59,8 hp.

But maximum BMEP is not produced at max.power rpm; it is produced at max.torque rpm. Hence the BMEP of 17 bar for the Aprilia RSA125.
4-stroke isn't that good .

Frits Overmars a écrit:

Mic a écrit:

If we use a 5% transmision loss on the RSA we get 31nm ( and 56,5hp ) this gives a BMEP of 15,6 bar.

Transmission losses are in the region of 5% per transmission step. From the crankshaft to the primary gearbox shaft you loose 5% of the crankshaft power. In the gearbox you loose another 5% of the input. So the 54 hp measured at the secondary gearbox shaft, was 95%*95% of crankshaft hp; crankshaft hp was thus 59,8 hp.

But maximum BMEP is not produced at max.power rpm; it is produced at max.torque rpm. Hence the BMEP of 17 bar for the Aprilia RSA125.
4-stroke isn't that good .

Max torque at outputshaft was 29,52nm @12517rpm and max power 53,6hp @13007rpm. With 2 times 5% transmition loss this would turn into 32,7nm and 59,4hp giving a BMEP of 16,4bar.

But 59,4hp sounds very high. I seems to remember having read that Jan Thiel said they reached a max of 56,5hp ( crankshaft power ) at Aprilia.

Was the engine further enhanced after his retirement?

I never talk about crankshaft HP as I have no means to MEASURE them!
We measured the power at the gearbox output.
How can some people be so sure about transmission loss without measuring it?
Once we did a test with a different primary drive, the gearbox turning faster.
We lost 0,5 HP

Many people talk about these 'crankshaft HP' because it looks better.
I think only people developing snowmobiles actually measure them!