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

motoholic71 a écrit:

Nowadays every car engine petrol or Diesel of any brand any kind will have an EGR valve. This began in the 90's in Europe.
It's not related to the Honda system.

This valve mixes some exhaust gas in the intake to bring down combustion temperature thus reducing NOX emissions. The valves are usually water cooled and are there just because of gas emissions laws, they don't help performance nor promote combustion and actually reduce engine life by completely filling the intake ducts with charred grease gunk.

Just saying this for the sake of knowledge that's all

Honda's hcci isn't exactly like diesel system, look at this link for more details

[Vous devez être inscrit et connecté pour voir ce lien]

Article intéressant qui explique bien comment fonctionne le système Honda 2T. Ils cherchent à réduire fortement les émissions polluantes ( Pb du 2T) en particulier à faibles et moyennes charges et régime, donc fonctionnent dans ces plages en "auto-combustion" si je puis dire avec un mélange très homogène et très pauvre, la compression fournit l'inflammation très rapide de la charge, sous des taux de compression modestes. Pour réduire les NOX dûs aux hautes températures, l'oxygène est réduit par un pourcentage de mélange de gaz d'échappement contrôlé par la fermeture partielle de la valve d'échappement ( celle que l'on voit sur les 3 dessins). A pleins gaz ( régime et charge) celle ci est ouverte et le moteur fonctionne en allumage commandé. Ouf, si j'ai bien tout compris, si un généreux traducteur veux bien translater pour nos amis éloignés, je n'en ai pas le temps ni le courage pour l'instant.
Dan

Si cela vous interresse, je peut scanner quelques articles parus dans l'excellent Mototechnologie et traitant de ce moteur Honda et de son système AR Combustion.

Dan j'en ai tiré les même conclusion mais sans être bien sûr de ma traduction.

Cassandre si tu trouve ton exemplaire plus rapidement que moi c'est volontier pour le scan, un déménagement récent à mené ma collec' de mototechno' dans un carton...

Ok pour les articles de Mototechnologie ,avec plaisir. Lorsque l'on voit les développements qu'entreprend Honda sur les moteurs 2T ( celui-ci et la version livrée par Marc, avec embiellage curieux permettant de modifier la course, + soupape), est-ce que l'on peut les accuser d'avoir voulu et obtenu la mort du 2T?
Dan

Dan42 a écrit:

Lorsque l'on voit les développements qu'entreprend Honda sur les moteurs 2T... est-ce que l'on peut les accuser d'avoir voulu et obtenu la mort du 2T?

Yes. Honda has a number of brilliant engineers, but unfortunately they are not in control of company policy.

The most powerful engine of the world? unfortunatly money...

Howard Gifford a écrit:

Jan I have a question about your RSA engine. What connecting rod length did you use and did you try other rod lengths? If so what advantages and disadvantages were there to either shorter or longer rod lengths?
Second question is could you or Fritz tell me approximately what the ignition timing curve worked best?
As you can figure out I am building a 250 parallel twin rotary valve motor using RSA clone cylinders.
I plan to spin it around 12000 rpm

Howard I have a pretty large series of quotes from Jan and Frits regarding the Aprilia details
(Likely to large to be posting here.)
My Aprilia album in the Kiwibiker site always has about 300 pics of the various Aprilia engines internals and so forth.(edit wow its closer to 500 pics)
[Vous devez être inscrit et connecté pour voir ce lien]
#You will need to sign and log into  the site to see them

From memory though Jan has said he never had a Negative result with a longer Rod only positive results on another forum.
In the RSA125, the con rod was lengthened from the RSW's 115 mm to 120 mm to create even more crankcase volume.
The longer rods also allow additional space for bigger rotary valves and thus straighter inlets
Pretty sure the original Rotax started with 110mm rods.
Short rods do however do somethings most people don't consider

Frits a écrit:

Short rods have a higher acceleration rate approaching and leaving TDC but a lower rate approaching and leaving BDC. That is all there is to it.

Woobly a écrit:

In a race engine at peak torque (same as peak power in many cases)the reeds do not start to crack open until the piston is travelling upward and is covering around 1/2 the transfer height.

Honda generally ran with short rods, maybe because due to their reed valve design they already had a large crankcase maybe there was front wheel clearance or maybe they were told to by the boss. Or maybe they found some benefit I have no idea and I don't think they will ever share thier knowledge and tell us like Jan and Frits do.
That said I think the later series of the NSR500 may have had 110mm rods. Pretty sure the Last A kit RS stuff was anyway.

Frits i think? a écrit:

There are several issues involved with the reed engine and its case volume - that has effects not seen in an RV setup.
The bigger the case the less are the pressure swings from piston movement and the pipe action ( assuming the same depression at the Ex port created by the pipe )around BDC.

Jan did not enlarge the crankcase volume on the Derbi reed valve engine; it was already big; a reed case has a lot more volume than a rotary valve duct.

I too would imagine that a reed engine would like an equally large case volume, so any pressure drop in the transfer ducts during scavenging is kept within limits without the need to instantly accelerate the contents of the inlet tract.

frits a écrit:

A difference that does come to mind: rotary valve engines like large carburettors; reed valve engines seem to care less. Apparently they compensate for smaller inlet duct cross-sectional areas by keeping the reeds open longer, something a basic rotary valve can't do.
Ah, but do they keep the reeds open longer ? i remember Jennings writing up reeds in Cycle mag and quoting an SAE paper by the Yamaha guys who developed the DT/RD series. They found that yes, the opening period varied - as did the timing - but at peak RPM the reed timing was the same as the roadrace rotary valve timing they were familiar with. That was with the very basic steel reeds of the period, i have no idea if the modern composite reeds act differently.

Frits a écrit:

Increasing the crankcase volume has several consequences. One of those is that the flow through the carb will be more even, less violent, which usually results in a leaner mixture.

Frits a écrit:

I posted the graph hereunder before, but it may not have sunk in with everybody, so I made an additional sketch.
When the crankshaft rotates away from TDC, the big end pin pulls the con rod downward. But because the rod also has to sway sideways, the small end drops more than the big end. The sketch (made with MS-Paint, so everyone can understand) shows a crankshaft with a 100 mm stroke, rotated through an angle alpha of about 70°.

On the right there is a 220 mm rod. Because of the swaying the small end has dropped an additional 4,8 mm.
On the left there is a 110 mm rod. Because of the swaying the small end has dropped an additional 9,9 mm, although the angle alpha is the same on both sides of the sketch. It's as simple as that.

[Vous devez être inscrit et connecté pour voir cette image]







I hope Frits doesn't mind me reposting these here.
Out of interest I am the guy that has the earlier DEA Cylinder Patterns.
If you want me to sent you the Word document that has most of the spec changes for the Aprilia engines message me your email details.
lastly there is a bunch of Kiwis that would love to speak to you regarding hydroforming pipes here.
[Vous devez être inscrit et connecté pour voir ce lien]

The RSA conrod was lengthened to improve inlet flow

Wow i have not read all pages yet but it is realy impressiv what knowledge here is written.

Most off my question are already done, i will read the rest first and then maybe ask something.

just finished going through some old motorcycle magazines ('76-'82), and scanned some interesting pictures :

[Vous devez être inscrit et connecté pour voir cette image]

very first Jamathi, but called Tansini at the time (1964) :
[Vous devez être inscrit et connecté pour voir cette image]

any comments/interesting anecdotes Jan how much power you got out of your first Tansini ?


comparison of the 1969 50cc champion Derbi to it's competitor's Kreidler and Jamathi :
[Vous devez être inscrit et connecté pour voir cette image]

The photos and their captions look strangely familiar to me Jan .

Frits Overmars a écrit:

The photos and their captions look strangely familiar to me Jan .

I've posted here ( [Vous devez être inscrit et connecté pour voir ce lien] ) some more

JanBros a écrit:

Frits Overmars a écrit:

The photos and their captions look strangely familiar to me Jan .

I've posted here ( [Vous devez être inscrit et connecté pour voir ce lien] ) some more

Jan your cylinder /port design has been the best arrangement to date and has been copied by several kart engine manufacturers. Imitation is the best form of flattery. To your knowledge has anyone made a copy of your cylinder with a larger bore than 54 mm? I am looking for a cylinder in the 65-68 mm diameter

As far as I know nobody has Howard

Howard Gifford a écrit:

Jan your cylinder /port design has been the best arrangement to date and has been copied by several kart engine manufacturers. Imitation is the best form of flattery. To your knowledge has anyone made a copy of your cylinder with a larger bore than 54 mm? I am looking for a cylinder in the 65-68 mm diameter

Hi Howard, there are 2 people in the UK who have made engines both 68 bore using the rsa port design
Viper racing uk who posts on here and THR . Both have CR250 02-07 stud pattern.

Hey Jan,
Have you ever tried 7 transfer system(like TZ250 4DP) on the RSA-RSW?Or Honda-type transfers with small divider and small C port,or you experimented and perfected the old rotax ports?

No, at Aprilia we made our own cylinders, based on the Rotax in the beginning.
I never thought that 7 transfers would be better.

I seem to have lost some pages. I was up to page 8 and now I'm back to page 4 in this section. Was it just me? Thanks

jfn2 a écrit:

I  seem to have lost some pages. I was up to page 8 and now I'm back to page 4 in this section. Was it just me? Thanks

Some comments were transferred to a new Ryger engine thread.

tjbw a écrit:

jfn2 a écrit:

I  seem to have lost some pages. I was up to page 8 and now I'm back to page 4 in this section. Was it just me? Thanks

Some comments were transferred to a new Ryger engine thread.

Here: [Vous devez être inscrit et connecté pour voir ce lien]

Thank you very much for the redirection.

Frits or Jan,
can you explain us why cast pistons seem to make better horsepower than the forged ones?
Cheers

In my opinion cast pistons have less friction than the forged