[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)

Here's a dyno run through the gears of a 6-speed Honda CR250 single.
You can see the EGT trace along the bottom.
This is with the EGT probe 150mm from the piston face.
On track we tune to a maximum of 650/670 deg C at the end of the fastest straight.


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Here's the MyChron data from a lap of Pembrey circuit in the UK. The EGT trace is the black one. You can see about 630 max

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Apart from the slightly low maximum, the dips in the EGT at gearchage indicate that the mixture is a little rich

I seem to remember Jan saying that Aprillia used to mount the EGT sensors in the manifold to get a reasonable sensor life. That is certainly true with a 250 single, which can shake your teeth out. At 150mm we are lucky to get 1 race meeting out of a sensor

 Sorry not Aprilia 125, but I thought might be of interest.


Best Regards

Ian

Here is our data pic, we scale at a finer value.
Phillips Island GP circuit Melbourne Australia 2013
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Hello,my name is Tomaž and i am a 2 stroke lover. In  my free time is mostly consumed by tomos mopeds and scooter engines. I have read this topic over and over again and it  just brings a smile to my face to see questions answered and knowledge shared  that i always wanted to know  (especially the practical stuff) by people who know what they are saying because they have tried it  and  understand it and also proved it on the track with astonishing results all these years   

I would like to ask a question about transfer dividers. I am trying to make them smaller to gain port area  like the RSA cylinder but i stopped because i dont know what shape i should  make them. Should they be straight  and made  thiner all the way  from the bottom of the cylinder to the  ports or  maybe leave a drop shape letting them to be wider  at the crankcase. The rsa ones are straight aren't they ?

I would be happy if someone could answer ,and i  am thanking everyone who participated in this topic and made it what is know.
A must read for all 2 stroke maniacs  

Hello everyone. I would like to ask a question regarding the position of the carburettor on the motorbike. The question is; does have a side-mounted carburettor (like on the RSW and many other side positioned disk-intake engines) any carburettion issues when the bike is cornering? Or does the centrifugal force keep the fuel where it's meant to be? Are the side-mounted carburettors any different than the typical carburettors? I have an Mikuni TMX 35.
I'm building an engine where, due to some space related issues, the carburettor can't be mounted "straight back" as usually is.
Thanks for Your answer!

fpayart a écrit:

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To dissuade you think I'm cheating, here are datas of a real Aprilia GP at Mugello last weekend.
You will notice that the exhaust temperatures are close to ours
Also the signal is a little more dynamic, it is that we use sensor slightly cheaper, bigger in diameter.

Is that from Peter Hartmann's RSW Francis ?

ice t a écrit:

Hello,my name is Tomaž....I would like to ask a question about transfer dividers. I am trying to make them smaller to gain port area  like the RSA cylinder but i stopped because i dont know what shape i should  make them. Should they be straight  and made  thiner all the way  from the bottom of the cylinder to the  ports or  maybe leave a drop shape letting them to be wider  at the crankcase. The rsa ones are straight aren't they ?

Welcome Tomaž.
Yes, the RSA and RSW transfer dividers are straight; the exhaust dividers are slightly curved around the central exhaust port. You can make all dividers straight.

roost a écrit:

I would like to ask a question regarding the position of the carburettor on the motorbike. The question is; does have a side-mounted carburettor (like on the RSW and many other side positioned disk-intake engines) any carburettion issues when the bike is cornering? Or does the centrifugal force keep the fuel where it's meant to be? Are the side-mounted carburettors any different than the typical carburettors?

Thanks to the leaning position in corners the fuel will always be where it's meant to be. Karts and sidecars using motorcycle carburettors have serious problems in that area.
There is no difference between side-mounted and rear-mounted motorcycle carburettors.

Hi

Frits did you know with what exhaust velocity can i calculate in a 125cc kart engine? it is a TM KV 95 rotary valve engine with a 39 Dellorto carburator.

The RSA hate about 590 m / s. am i right?

Thanks Manuel

Manuel Rainer a écrit:

Frits did you know with what exhaust velocity can i calculate in a 125cc kart engine? it is a TM KV 95 rotary valve engine with a 39 Dellorto carburator. The RSA hate about 590 m / s. am i right?

This velocity can be anything from 400 to 700 m/s, depending on ignition timing, mixture strength and compression ratio, so I cannot give you a definite value, Manuel.
I think the most instructive way will be to measure the engine's torque curve and the exhaust pipe dimensions, and calculate back. That way you will gain much more insight than by just accepting some value I might quote.

Citation :

Is that from Peter Hartmann's RSW Francis ?

Answer from Damien (his son):
Yes, it is Peter's RSW

(I am replying for Francis as he is at the hospital for the moment and would love to discuss with you !
His back operation is a success and he needs some time to recover now)

fpayart a écrit:

Citation :

Is that from Peter Hartmann's RSW Francis ?

Answer from Damien (his son):
Yes, it is Peter's RSW

(I am replying for Francis as he is at the hospital for the moment and would love to discuss with you !
His back operation is a success and he needs some time to recover now)

I am happy to hear the operation went well!

Excellent news !

great to hear!

Jan, have you been in Sepang at the MotoGP race?

[Vous devez être inscrit et connecté pour voir ce lien] - "Il mago" i like that!

koenich a écrit:

great to hear!

Jan, have you been in Sepang at the MotoGP race?

[Vous devez être inscrit et connecté pour voir ce lien] - "Il mago" i like that!

Yes, I was invited by Lucio Cecchinello, it was very nice!

Jan wearing a Honda shirt!

Jan Thiel a écrit:

fpayart a écrit:

(I am replying for Francis as he is at the hospital for the moment and would love to discuss with you ! His back operation is a success and he needs some time to recover now)

I am happy to hear the operation went well!

+1  

Thanks for the update Damien, great to hear the operation went well. Viper Racing UK wishes Francis a speedy recovery  

Best Regards

Ian:D

Heal well Francis from all of us at BRC Engineering canada.

fpayart a écrit:

Citation :

Is that from Peter Hartmann's RSW Francis ?

Answer from Damien (his son):
Yes, it is Peter's RSW

(I am replying for Francis as he is at the hospital for the moment and would love to discuss with you !
His back operation is a success and he needs some time to recover now)

great news for your family  

Frits Overmars a écrit:

Manuel Rainer a écrit:

Frits did you know with what exhaust velocity can i calculate in a 125cc kart engine? it is a TM KV 95 rotary valve engine with a 39 Dellorto carburator. The RSA hate about 590 m / s. am i right?

This velocity can be anything from 400 to 700 m/s, depending on ignition timing, mixture strength and compression ratio, so I cannot give you a definite value, Manuel.
I think the most instructive way will be to measure the engine's torque curve and the exhaust pipe dimensions, and calculate back. That way you will gain much more insight than by just accepting some value I might quote.

hi

Thanks Frits

Frits maybe you can explain the calculation method with the engine's torque curve and the exhaust pipe dimensions.

thanks Manuel

Manuel Rainer a écrit:

Frits maybe you can explain the calculation method with the engine's torque curve and the exhaust pipe dimensions.

Just take the rpm value that you found for maximum power, use it in my simple exhaust concept
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and vary the speed of sound value in that concept until the calculated length coincides with the length of your pipe.

Hello gentlemen.  Great thought provoking reading here, thank you to all.

I am designing a "Mule" test engine for development of a 125cc and 250cc twin cylinder engine for superkart racing. In the past 9months we have had the most consistent success with our twin that we have ever had.  Like most superkart engine manufacturers, we copied the work of Jan and Frits. Only now we are understanding that the kart needs to be tuned differently from the bike.  As Francis stated, the kart is at 100% throttle for sometimes 80% of a lap.  I would like to ask this forum to have input on the design of the Mule which with then be developed into a new twin.  The mule will be a single cylinder 125cc without gearbox or balance shaft (for simplicity).

Our current Mule uses the following:
BRC cylinder (Aprilia APC copy) 197 degree exhaust
120mm con rod
115mm Vertex Aprilia GP piston with 0.8mm ring
42mm VHSG with power jet
NJ205 main bearings
124mm diameter carbon disk valve timed at 137/87.
Tungsten weighted crankshaft, 47mm long crank pin, 20mm pin diameter
655cc crankcase volume
Type 21 exhaust copy in steel


Current thoughts
Modify cylinder to be like APF (RSA)
120mm rod
NU main bearings with 2 piece inner race
EFI
135-140mm diameter disk
Wider, bigger diameter, and higher mass crankshaft, 20mm pin
675-700cc crankcase volume
DC ignition with internal crankshaft pick up like RSA
New exhaust to allow for 14,500 max rpm, peak power to be 13,000-13,200 rpm

I would appreciate any and all input to design this engine.  The EFI system is currently being bench tested with excellent results.  With a 41mm butterfly throttle body we are at the same level as we have been with a 43mm VHSG. I am finishing our own throttle body which is a 43mm slide type. We see 49hp at 12,800rpm with good overrev power to 14,000rpm.

I am happy to share pics if I can figure out how to post them.... Any tutorials?

Didn't work from my iPad...

Hello Riley :
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If you are getting 49 HP with an APC cylinder and a type 21 exhaust, you are doing very well, Riley.
I am eagerly following your EFI proceedings on facebook.

Frits,

What size of disk valve would you like to use?

Hi Riley

If you want to sell engines here in europe you should test with non power jet carb as power jets isn't allowed by CIK.

I also remembering Francis writing that the RSA used 146/93 disc timing.

I've converted my old Rotax 256 to use 130mm. discs, works fine.