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

Frits Overmars a écrit:

Bob van der Zijden a écrit:

Serious racing costs serious money. Low budget racing is ok but don't expect too much technically seen.

Once upon a time there were two friends, Jan Thiel and Martin Mijwaart..... Need I say more, Bob?
Yes, they were the exception to the rule, but why shouldn't there be other exceptions nowadays that we don't know about yet?
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This shed was the origin of 26 constructor's world titles and 25 rider's world titles.

koenich a écrit:

99% of the folks working on 2-strokes do this as a hobby and due to pure enthusiasm. They spend their free time plus earned money in order to have fun and in the best case learn something.

So let us try to encourage them!

Frits, this post and photo made my day. Thank You!!!

GREAT photos !

What year ?

What exact unit was being tested ?

I don't see a " Disney Land " decal on that low-tech coil ! lol !! ( maybe Bosch ? from a V-Dub / Porsche )

Bob : This looks more * In a Gadda da Vida * than Freddy & His Dreamers.

Just looking at the great Freddy Mercury. Makes me so sad he isn't around anymore. Listened to the full length of In a gadda da vida (17 minutes) fantastic, I knew the music buy not the title.
By the way, has anybody had already a look at Yoshimure's MJN carb? Very promising I think. However I reckon my Motec controlled 60 bar pulsed injection under the piston of a Honda RS125 1n 1998 is difficult to beat. Only no dough and assistance to develop. That's also part of life. Certain people on this forum do know about this project but never dare to mention it ...

Well, I always welcome any / all info.

ambike a écrit:

GREAT photos ! What year ? What exact unit was being tested ? I don't see a " Disney Land " decal on that low-tech coil  (maybe Bosch ? from a V-Dub / Porsche ).

I didn't know the above photo, but my guess: Piovaticci, 1975. Next to Jan is works rider Eugenio Lazzarini.
The engine will officially have been a Piovaticci, but in reality it still was a 50 cc Jamathi, built in Holland and taken to Italy when Jan and Martin got their works contract with Piovaticci. The picture below shows Jan with his 'baby'.

The coil is indeed an oil-filled Bosch unit, developed for Porsche. You may call it low-tech, but these coils were still used on all Garelli bikes. More modern, smaller, lighter Japanese coils could never match the power of the old heavy Bosch units.
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Those Bosch coils gave 0,3HP more per cylinder than the Krober coils, and eliminated misfiring.
My very good friend Han Schummelketel gave me this idea!

Bob van der Zijden a écrit:

Just looking at the great Freddy Mercury. Makes me so sad he isn't around anymore. Listened to the full length of In a gadda da vida (17 minutes) fantastic, I knew the music buy not the title.
By the way, has anybody had already a look at Yoshimure's MJN carb? Very promising I think. However I reckon my Motec controlled 60 bar pulsed injection under the piston of a Honda RS125 1n 1998 is difficult to beat. Only no dough and assistance to develop. That's also part of life. Certain people on this forum do know about this project but never dare to mention it ...

Bob,  wouldn't you be the ideal person to tell us about this  (very interesting) item ?  
If I may ask :  was your setup comparable as to what Harald Bartol did with the ktm,   but only several years later ?   Or did you choose a different location for the injector ?  
And also :  with the arrival of modern injection kits like for example the ecotrons [Vous devez être inscrit et connecté pour voir ce lien]   would this be a good choice for the project that you were/are doing ?

Han Schummelketel was a highly qualified R&D engineer who went fro Philips to the Technical University Eindhoven. He was responsible for the electronic design & circuitry that Mr Plat from Motoplat got thru Jan Thiel who was in need of a better ignition when starting at Bultaco.
More about the mentined coils as chosen by Han Schummelketel ( sadly he died of cancer about 10 years ago, I'm proud he was a fantastic friend as Jan Thiel is already some 60 odd! years). The Bosch coil was the one made for Porsche for their HKZ (Hochleistungs Kondensator Zündanlage = cdi in German) for the 911 flat 6 cylinder engines.
The data behind coils in cdi"s are: 1/2*C*V=1/2*L*I squared. In words : the energy stored in a capacitor delivers 1/2*L*I squared. C is the capacity in Coulombs, V the charging voltage. L the self inductance of the coil that receives the energy from the capacitor and I the current .This shows that in order to get the highest current the L being the self inductance has to be as low as possible. During trials on my dynamic ignition test rig we measured already a lot of HT coils, the best one so with the lowest self inductance up to now is MSD's pn #8232.
Rgarding Harald Bartols injection: this was a set up to fight detonation. It is a variation on my system from 1998. Harald did not have the unique injector we made and used. Most probably the fastest electro-mechanical injector ever made. It was the design of a briljant engineer of the Technical University Eindhoven by the name of Wout Boer. Harald then got the data of my injection project with 2 sudents in my shop and made his anti detonation version of it. I know Harald already for about 40 years. Bartol use a small pisser device as injector with very lo pressure whilst I applied up to 60 bar with a Motec M4 ecu and an ACCEL 300+ cdi, a design of the man behind the first real plasma ignition PAUL PORRECA who developed the 300+ at Adrenaline Research for Mr Gasket the owner of Accel. By the way this is a real good cdi!

Very interesting info Bob.

However if you have an equation that gives us spark duration that would be alot handier.

I see the MSD 8232 (discontinued) has a primary resistance of 0.9 ohms.
Compare that to the OEM ND coils fitted to my RGV of 0.7 ohms. Hmmm.
Did i miss something.

The only thing I can produce are comparisons between various coils. With a particular coil it's possible to go for high current and short duration. The other side of this is lower current and longer duration. On our dynamic test rig we are able to measure and show it. Recently I bought a new digital scope unfortunately without the calculating mode but with the possibility to attach a memory stick The frozen measuring picture can be put on the stick and the via the computer be transferred to the calculating part of the excel program to show the area under the curve. But being a mechanical farmer of 75 odd years I first need to learn how to do it. When so far I'll be able to produce data.
By the way the MSD 8232 has a primary resistance of only 0.09 ohm and therefor a very low self inductance. About hig current-short duration or lower current-longer duration I can only ask here : what do our stinking 2strokes need?

Here is a pic of the 1975 Piovaticci 125 cc twin

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1975 Piovaticci 50 cc single :

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Source Siegfried Rauch

Bob van der Zijden a écrit:

... being a mechanical farmer of 75 odd years...

Does this mean that you are past 75, but can't remember how far? I can't resist pulling your leg, Bob...

Citation :

About hig current-short duration or lower current-longer duration I can only ask here : what do our stinking 2strokes need?

In any case a long duration; longer than a foul-stroke. But a wide plug gap won't hurt either, as long as the ignition is up to it. A wide gap calls for a high initial tension, and this call is aggravated by the squish-induced turbulence that tries to blow the ionized gases aside before they can form a conductive channel from one plug electrode to the other.
Once this channel stands, there is no need for quite such a high tension any more. In principle we could now put the primary tension from the ignition unit directly to the spark plug instead of sending it through the coil. That way the capacitor might not discharge quite so rapidly and we'd have a hot long-lasting spark.
Such systems do exist and they are generally called plasma ignition, although I doubt whether this name is justified.
In any case the engine likes it, but the spark plug does not; this 'plasma' ignition eats plug electrodes for breakfast.
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The only thing that really counts after ionisation is the current in Amps,, that ignites the mixture between the electrodes . Also very important is the grade of ionisation for which a lot of electrical energy does very well. Furthermore I think the only proper spark plugs are the surface gap types, a lot of energy however is required to let these function well. Another feature of these plugs is the minimal disturbance of the combustion chamber profile and also their minimal dead volumetric capacity.

Bob van der Zijden a écrit:

Furthermore I think the only proper spark plugs are the surface gap types, a lot of energy however is required to let these function well. Another feature of these plugs is the   minimal disturbance of the combustion chamber profile and also their  minimal dead volumetric capacity.

bob i dont know much about spark plugs but when you refer to surface gap types, do you meen something like this ?

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This is a surface discharge plug

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According to Christopher Jacobs they are actually designed to provide a solid-state medium for the electrons to migrate across, thus making it easier for the ignition and often masking the problem of weak ignition.

In an engine with a good, powerfull, ignition they will not increase horsepower.

Senne s a écrit:

This is a surface discharge plug. According to Christopher Jacobs they are actually designed to provide a solid-state medium for the electrons to migrate across, thus making it easier for the ignition and often masking the problem of weak ignition.

It takes only very little fouling to create a conductive path over the insulator of a surface gap plug, and once that happens, the electrons can migrate without even having to create a spark.  I tend to agree with Bob:

Bob van der Zijden a écrit:

... a lot of energy however is required to let these function well.

Bob van der Zijden a écrit:

By the way the MSD 8232 has a primary resistance of only 0.09 ohm and therefor a very low self inductance

DOH! Does anyone know a good optician, my eyeballs can't spot decimal points anymore.

Bob van der Zijden a écrit:

About hig current-short duration or lower current-longer duration I can only ask here : what do our stinking 2strokes need?

As Frits said, as long a duration as possible. 2str don't have the luxury of Tumble and Swirl that 4str can generate in-cylinder prior to ignition, so any additional spark duration helps that initial flame kernel get up to size before lights out.

Frits Overmars a écrit:

.....and this call is aggravated by the squish-induced turbulence that tries to blow the ionized gases aside

Not sure I agree with this one Frits. By the time any squish-induced turbulence gets into gear, the spark event is very much over and the flame kernel is doing a good job of filling the combustion space ie. its self sustaining and larger than its component turb eddies. I think it was you who said all squish does is to clear out all combustible end gases from the periphery of the chamber. No gas, No deto

Dont forget the overlap in boundry layers that does a lot to

As stated before it's the current in Amps that ignites the non homogeneous mixture . In my opinion the amount of current is more important than it's duration. As mentioned before the higher the grade of ionisation the better can the current do it's job, that's my idea which I gladly replace for a better one...
One more remark about plugs : it's most interesting to Google about -side gapping-, this only applies to a certain kind of plug. On a Dutch 23 HP 50cc it gave almost 0.5 HP. And on a Rotax Max kart the lap time on the tiny track of Strijen in Holland (not far away from Rotterdam) went from 33 to 32.6 seconds. Whilst the best time then in 2012 or 2013 was 32 seconds. These are just a few practice examples that show the importance of ignition, without scientific data.

About the boundary layers please explain. Im eager to learn.

I read it on page 7.

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Sorry for others but its dutch.

Side Gab factory BoB ( LoL )[Vous devez être inscrit et connecté pour voir cette image]

Side gapping may be ok for your 2.50euro copper and steel plugs

But for my 50euro rare earth element fine wire racing plugs, i'll stick to gapping them the old fashioned way

dutch fisher a écrit:

As Frits said, as long a duration as possible. 2str don't have the luxury of Tumble and Swirl that 4str can generate in-cylinder prior to ignition, so any additional spark duration helps that initial flame kernel get up to size before lights out.

Two-strokes do not have any swirl to speak of, unless the transfers are grossly asymmetrical, but they can have every bit as much tumble as a four-stroke. But first and foremost they have squish; much, much stronger squish than a four-stroke with its cluttered head and piston crown shapes.

Frits Overmars a écrit:

.....and this call is aggravated by the squish-induced turbulence that tries to blow the ionized gases aside

dutch fisher a écrit:

Not sure I agree with this one Frits. By the time any squish-induced turbulence gets into gear, the spark event is very much over...

You may want to take a look at the table hereunder, Dutch. It shows the squish calculations for an Aprilia RSA125 at 13000 rpm with a static squish clearance of 0,7 mm (no decimal points here; in Europe we use decimal commas).
But don't be misled by those 0,7 mm. Taking the dynamic stretch into account, the actual squish clearance becomes much tighter, and the squish velocity benefits.
At 13000 rpm the RSA has an ignition timing of 14° before TDC. Care to look up the squish velocity at that crank angle?
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Citation :

I think it was you who said all squish does is to clear out all combustible end gases from the periphery of the chamber. No gas, No deto

I did say that at squish clearance zero there would not be any combustible gases left in the periphery of the chamber.
That's right: no gas, no deto.
But I never said that this is all squish does; it also slings around burning lumps of mixture, starting simultaneous fires in every corner of the combustion chamber. Without squish the flame speed would be far too low for this engine.

Before we go too far into the wonderful world of squishing.
It might be an idea to pinpoint in time your blown ionized gases in relation to the spark event.
Just so we are all singing from the same hymn sheet