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

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MANETON

MANETON

Nombre de messages : 1557
Localisation : *
Date d'inscription : 26/09/2010

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
MessageSujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)   [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Icon_minitimeLun 4 Mai 2020 - 12:51

Calorstat is an old trademark. We, French, use this word but most of the (modern) time it is to talk about three-ways thermostats.
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Frits Overmars

Frits Overmars

Nombre de messages : 2345
Age : 71
Localisation : Raalte, Holland
Date d'inscription : 12/10/2010

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
MessageSujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)   [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Icon_minitimeLun 4 Mai 2020 - 18:58

Vannik a écrit:
Frits, thank you this is good info. Further on the topic of side vs rear entry: Has the difference between left and right hand transfer port flow been measured and if so was it noticeable? It seems the one side has a nicely shaped transfer duct entry in the crankcase while the other side it is "destroyed" by the inlet port. So if there is a worthwhile difference that will be another advantage to the rear inlet.
This is a question for Jan to answer. To be honest, Jan is the best person to answer all Aprilia-related questions. And all Garelli-related questions. And all Jamathi- and Piovaticci- and Bultaco-related questions. Then I can take a little forum-sabbatical Wink
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carlovitch1



Nombre de messages : 382
Localisation : Pays Catalan
Date d'inscription : 20/05/2018

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
MessageSujet: Re: [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)   [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Icon_minitimeLun 4 Mai 2020 - 20:35

Good evening everyone, hope you all are in good health condition.

While we are talking about old GP bikes, I have 2 questions for Jan, Frits or anyone knows:
1- (I think this one is for Jan to answer) About the 50cc Bultaco of 1978: this bike finished all the races of the year while the other brands were often breaking their engines. What was the trick that made the difference?

2- About the 250/350 Aermacchi/Harley that allowed Walter Villa to clinch 4 world titles, I've read in the litterature that the transfers were using a special trick that gave their engine an advantage over the competitors, anyone knows what this trick was?
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Frits Overmars

Frits Overmars

Nombre de messages : 2345
Age : 71
Localisation : Raalte, Holland
Date d'inscription : 12/10/2010

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carlovitch1 a écrit:
About the 50cc Bultaco of 1978: this bike finished all the races of the year while the other brands were often breaking their engines. What was the trick that made the difference?
Jan is of course the right person to answer that question, but I suppose he is sleeping now. What I can remember is, that his Bultaco had about the same maximum power as the Van Veen Kreidler, but with more low-down power and with a lower maximum rpm, which of course improved reliability.
carlovitch1 a écrit:
About the 250/350 Aermacchi/Harley that allowed Walter Villa to clinch 4 world titles, I've read in the literature that the transfers were using a special trick that gave their engine an advantage  over the competitors, anyone knows what this trick was?  
The 'special trick' mentioned in the literature was the fifth transfer port, fed through a hollow center bridge in the inlet duct.
But I doubt if it was really that helpful. I tried it myself, and after testing it on the dyno I filled this fifth port with Devcon and removed the inlet bridge.
The engine gave more power without that bridge and port.
On the picture of the Aermacchi cylinder below you can just see the duct and the fifth port, if you know what you're looking for.
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carlovitch1



Nombre de messages : 382
Localisation : Pays Catalan
Date d'inscription : 20/05/2018

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Thanks a lot, Frits for your quick and precise answers, as always.[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 771973

I wonder if a book exists that would explain history of all the racing 2 stroke evolutions, from the very beginning to the last racing engines. It is often good to know where the improvements came from.

I have another question, which is maybe trivial for some of the forum members, but not easy for me: I'm actually thinking of building a 50cc prototype for having fun on our local race track, and I have hard times figuring out which cooling radiator size I need to use to keep the engine within the specified temperature (the manufacturer of the top end says it needs to run at about 50°C). Any rule of thumb I could use to get at least an idea?
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Jan Thiel



Nombre de messages : 506
Age : 79
Localisation : Bangkok
Date d'inscription : 12/10/2010

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
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The Bultaco 50 did not rev so much, done to avoid friction.
I did that after seeing a Yamaha SAE paper...
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carlovitch1



Nombre de messages : 382
Localisation : Pays Catalan
Date d'inscription : 20/05/2018

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
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Thanks for the explanation, Jan, it makes sense, but probably not that easy to do on a very small engine.
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Frits Overmars

Frits Overmars

Nombre de messages : 2345
Age : 71
Localisation : Raalte, Holland
Date d'inscription : 12/10/2010

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carlovitch1 a écrit:
I'm actually thinking of building a 50cc prototype for having fun on our local race track, and I have hard times figuring out which cooling radiator size I need to use to keep the engine within the specified temperature (the manufacturer of the top end says it needs to run at about 50°C). Any rule of thumb I could use to get at least an idea? 
I have never thought about a rule of thumb for radiator sizes, but the rule of thumb for coolant temperature is simple: the colder the better,
so I would go for 40°C rather than 50°C.
Here are some pictures of Freetech50 bikes that may give you an idea about radiator sizes.The first picture shows the actual European champion.
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carlovitch1



Nombre de messages : 382
Localisation : Pays Catalan
Date d'inscription : 20/05/2018

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Thank you very much Frits !
As I'm on a budget, I've been frightened by the cost of so-called "competition" radiators without having any guarantee nor indication to know whether they will match the need.
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Frits Overmars

Frits Overmars

Nombre de messages : 2345
Age : 71
Localisation : Raalte, Holland
Date d'inscription : 12/10/2010

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carlovitch1 a écrit:
As I'm on a budget, I've been frightened by the cost of so-called "competition" radiators without having any guarantee nor indication to know whether they will match the need.
"Competition" in racing is more or less the same as "Bio" in a grocery shop,  where it means "costs three Euro more".
Unless you are planning to become the next 50cc world champion, you might take a look at a car or motorcycle scrap yard.
You may see radiators that are too big in size for your needs, but there is no such thing as too much cooling capactiy.
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carlovitch1



Nombre de messages : 382
Localisation : Pays Catalan
Date d'inscription : 20/05/2018

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Yes, Frits, this is exactly what I intend to do, I will go to the closest motorcycle scrap yard and check what I can find. From the pictures you posted, the needed size is somewhat 300 x 250mm.
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SLT



Nombre de messages : 133
Localisation : Bourgogne, France
Date d'inscription : 07/06/2014

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MessageSujet: Aprilia   [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Icon_minitimeMar 5 Mai 2020 - 21:07

Hello Frits, and Thanks for explanations !
Frits Overmars a écrit:
With a 125cc engine, the target temperature was 40°C. Even colder would have been even better for power, but during the GP season some races were run with outside temperatures above 30°C and then cooling the engine below 40°C would have required a huge radiator, which due to its air resistance would have negated the power gain. For the same reason, the target temperature for the 250cc engines was 50°C.

ok, I understand why only one cooling system ...And I 've seen your picture about actuel race 50cc radiator size...
The RSA motor used only water in cooling system  ?

Frits Overmars a écrit:
I was not familiar with the name Calorstat, so I googled it, and it appears to be a normal open-or-closed thermostat. The 45°C treshold temperature sounds fairly good for a 125cc engine, but the problem is that it will allow zero water circulation until it reaches that temperature. Because of this zero circulation, large temperature differences will develop between the hot and cold areas of the cylinder. And when the thermostat finally opens, very cold water from the radiator is suddenly admitted to the cylinder, which can lead to deformation ans seizures.

It is better to use a three-way thermostat that always permits water circulation through the cylinder, and switches over from a cooling circuit excluding the radiator, to a cooling circuit including the radiator, when the appropriate temperature is reached.

Sorry For "Calorstat" : I just used this word because it's called like that on the Rotax Parts WebSite where I bought it ! There were 2 possibilities 45 or 58°  
So, I will try (as soon as possible...) on my Aprilia the bypass with 45° 3 ways thermostat : with your explanations, I understand it's better ! Thanks

Frits Overmars a écrit:
The second disadvantage was that, because of the rear disc, there was no room on the RSA for the rear-exiting exhaust of the RSW.
On the RSA the cylinder had to be turned around, so the exhaust exited at the front. This made it necessary to place the engine further rearward, away from the front tire, which lead to a weight distribution that was not as good as it had been on the side-disc RSW.

Jan Thiel a écrit:
Another disadvantage of the rear inlet was the curve in the exhaust
A straight pipe gave more power.
And also the necessary long tailpipe cost some power.....
There were some carburation problems when braking too!

Frits and Jan ; OK I only thought about straight exaust...  but have you got an idea of Power difference on RSA/RSW for this ? I saw 125 GP Exaust Pictures, and Tailpipe seems -to me- effectively to be rather short ones ?  Could you explain me what 's the impact of tailpipe lenght and diameter ?  
Thanks,  Stéphane
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Frits Overmars

Frits Overmars

Nombre de messages : 2345
Age : 71
Localisation : Raalte, Holland
Date d'inscription : 12/10/2010

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SLT a écrit:
The RSA motor used only water in cooling system?
I seem to remember that according to the Technical Regulations "only water is allowed as a liquid coolant, whether or not mixed with ethanol. Other antifreeze agents are not allowed. A maximum of 2 % anti-corrosive may be added to the coolant".
The reason for excluding antifreeze is, that while a water spillage on the track can quickly be cleaned up, antifreeze is slippery and does not evaporate, so it could make the track unusable for a longer period of time.
Jan Thiel a écrit:
Another disadvantage of the rear inlet was the curve in the exhaust. A straight pipe gave more power. And also the necessary long tailpipe cost some power.
SLT a écrit:
... have you got an idea of Power difference on RSA/RSW for this ?
I have no data at hand, but I think the difference was not very big. And in some cases a pipe with a curved header actually produced more power than an straight pipe.
SLT a écrit:
I saw 125 GP Exaust Pictures, and Tailpipe seems -to me- effectively to be rather short ones ?  Could you explain me what 's the impact of tailpipe lenght and diameter ?
The tailpipe of the RSA125  is about 10 times longer than the tailpipes of the RSW125, the RSW250 and the RSA250, while all other pipe dimensions are supposed to be identical.
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There is a method to minimize the influence of the tailpipe length: place a restrictor between the endcone and the tailpipe, and give the tailpipe a clearly bigger diameter than the restrictor. On the exhaust concept below you can see what I mean. D5 is the restrictor diameter and D6 is the tailpipe diameter.
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LeonardoMRF2



Nombre de messages : 24
Localisation : Brasil
Date d'inscription : 28/04/2019

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Frits I'm sorry if you said that here, but I'm curious about your opinion on the reasons for an engine with a compression ratio of 9: 1 for example, having better performance, I've used 10.5: 1 and it worked well, I have some thoughts about it, however your explanations always make more sense to me than my thoughts
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JanBros



Nombre de messages : 278
Localisation : Belgique
Date d'inscription : 05/12/2011

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my guess his answer will be :
less compression means less of the energy is used to push the piston down, so there is more energy left in the exhaust gases and they make your pipe work harder, pushing more fresh charge in the cylinder and more mixture in the cylinder makes the engine more powerfull.

but I'm not a good "guesser" so he may come up with another explanation ... Very Happy
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Frits Overmars

Frits Overmars

Nombre de messages : 2345
Age : 71
Localisation : Raalte, Holland
Date d'inscription : 12/10/2010

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LeonardoMRF2 a écrit:
Frits I'm sorry if you said that here, but I'm curious about your opinion on the reasons for an engine with a compression ratio of 9: 1 for example, having better performance, I've used 10.5: 1 and it worked well, I have some thoughts about it, however your explanations always make more sense to me than my thoughts
JanBros a écrit:
my guess his answer will be :
less compression means less of the energy is used to push the piston down, so there is more energy left in the exhaust gases and they make your pipe work harder, pushing more fresh charge in the cylinder, and more mixture in the cylinder makes the engine more powerfull.
But I'm not a good "guesser" so he may come up with another explanation Very Happy
Your guess is as good as mine, Jan Wink
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LeonardoMRF2



Nombre de messages : 24
Localisation : Brasil
Date d'inscription : 28/04/2019

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thank you Jan, thank you Frits
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SLT



Nombre de messages : 133
Localisation : Bourgogne, France
Date d'inscription : 07/06/2014

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Hello Frits,
Thanks for last answer, and sorry for delay !
[quote="Frits Overmars"][There is a method to minimize the influence of the tailpipe length: place a restrictor between the endcone and the tailpipe, and give the tailpipe a clearly bigger diameter than the restrictor. On the exhaust concept below you can see what I mean. D5 is the restrictor diameter and D6 is the tailpipe diameter./quote]
Ok I understand, but, when you say "Taipipe clearly bigger" you mean as big as 2 mm for exemple ? I saw 125GP and I was surprised by taipipe and silencer diameters ! What whoud be a good ratio between silencer pipe and tailpipe diameter ?
Stéphane


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JanBros



Nombre de messages : 278
Localisation : Belgique
Date d'inscription : 05/12/2011

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I think you'll find your answer in Frits' FOS exhaust concept a some posts back.
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SLT



Nombre de messages : 133
Localisation : Bourgogne, France
Date d'inscription : 07/06/2014

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Hello Jan,
Thanks for help
I had saw Frits' FOS Exaust concept, which is very well -of course- , but I thought it was general trend for "begining tuners" -I may haven't understood : Frits, sorry for that in this case-, and I was wondering to Frits for 125 GP like Aprilia RSA or RSW exaust ; Maybe it's the same answer, but I'm not sure, it' s why I asked him ! I may have badly explain ! (and your're right..., I have probably to read back to see 125GP silencer answer Embarassed )
Stéphane
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LeonardoMRF2



Nombre de messages : 24
Localisation : Brasil
Date d'inscription : 28/04/2019

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
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Mr.Jan and Mr.Frits don't know if this was done and if it still has this information, what is the weight of the complete aprilia RSA engine and the weight of the individual components, pistons, connecting rod, crankshaft ...
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bentou

bentou

Nombre de messages : 1966
Age : 60
Localisation : Hauts de Seine
Date d'inscription : 06/04/2012

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 Empty
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And please, can you start a new production line ???
125 single, 250 twin, 500 4 and why not 750 6 ??? [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 43 727249
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