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

carlovitch1 a écrit:

Maybe the use of standard tubes (for 4 strokes) is reducing the vibration issue. 4 strokes pipes shapes are generally less complex than 2 strokes ones.

In Moto3 class , you'll find your last HP in the exhaust system , nowhere else , and surprisingly a great knowledge/experience in 2 stroke exhaust helps a lot



.

aparently there was an error in a BMEP-link in my 2-stroke excel, fixed it now.

and now there is a way of printing the portmap to actual size, so you can print it, cut out the ports and place it in your cylinder to see where you have to grind the ports some more.


anyone used it already ? any comments ?


new download links to version 1.1 :
excel : [Vous devez être inscrit et connecté pour voir ce lien]
manual : [Vous devez être inscrit et connecté pour voir ce lien]

xlsm no found

Yes, JanBros, I do confirm: the link does not work.

fixed it ;-)

Thanks, JanBros !

carlovitch1 a écrit:

About the pipe material selection, being a materials engineer (for pressure vessel engineering, not vehicles), I'm a bit surprised that stainless steel is considered. Is this austenitic SS like 304/316L or a specific grade? Austenitic stainless steel does not like vibrations and is also very sensitive to cold work effects compared to carbon steel. My idea was that they will not last long.

Nearly all car exhaust lines are out of stainless steel - grade depends on exhaust gas temp and optic requirements. Even fabricated manifolds (deep drawn or bended pipes etc) are common...

Do you know some of the exact stainless steel grades used for car exhausts? I would be insterested to know whether they are austenitic or other kinds.

I think 304L and 316L are good, L is for low carbon, better to weld assembly . No mixed parts whith carbon steel, passivation after welding.
Dan

These are indeed austenitic grades, maybe they resist better on 4 strokes because of lower vibration frequency and use of real tubes almost everywhere, so less welding and forming residual stresses.

carlovitch1 a écrit:

Do you know some of the exact stainless steel grades used for car exhausts? I would be insterested to know whether they are austenitic or other kinds.

Standard materials and therefore readily available...:
- Ferritic grades: 1.4509 (441), 1.4512 (409)
- Austenitic grades: 1.4301 (304), 1.4828 (309)

To build a SS 2-stroke exhaust I'd recommend using 1.4301 or 1.4509.

Most important thing is to use the right weldfiller due to different thermal expansion ratios in between austenitic and ferritic grades:
- Ferritic weld filler: 1.4509 or 1.4511
- Austenitic weld filler: 1.4370

You can mix SS with mild steel but always use higher grade weld filler (1.4370 for e.g.).

Thanks for this info Dan42 and koenich. For me the easiest available is 1.4307 (304L). I will give it a try.

Stainless steel is a work hardening material, much like titanium thus it will crack quite quickly compared to mild steel.
The most suitable grade of stainless steel for exhaust piping is G321, this grade will provide a longer useful life compared to other austenitic grades.
Shrinkage stresses within the welded joints can reduce the useful life cycle of a pipe immensely.
Perfectly tight fit ups of each joint is highly recommended, at every spot that a gap is present the shrinkage forces to the material directly adjacent to the weld will be pulled towards the welds centre as the weld solidifies resulting in this area being highly stressed, much like a tightened guitar string. These highly stressed zones fundamentally due to gaps before welding will be where the cracks begin.
Obviously there can be numerous additional factors aswell however gaps are the most prevalent error.

Ok, G321 S.steel is 304 added whith titanium, better for corrosive environment, the brother of 316Ti that we used in such conditions.
Dan

It is the Nickle % increase that makes 321 superior
Turbo turbine wheels are pro dominantly made from inconel. This has a very high nickle content, nickle increases strength at elevated temperatures, increases toughness, oxidisation resistance, creep resistance to name a few over 316 & or 304.
It’s suited far better to an exhaust environment than any other grade of stainless steel period.
Probably explains why it’s used in the aviation industry

RAW a écrit:

It is the Nickle % increase that makes 321 superior
Turbo turbine wheels are pro dominantly made from inconel. This has a very high nickle content, nickle increases strength at elevated temperatures, increases toughness, oxidisation resistance, creep resistance to name a few over 316 & or 304.
It’s suited far better to an exhaust environment than any other grade of stainless steel period.
Probably explains why it’s used in the aviation industry

Tell that to hundreds of millions of car exhausts made out of the grades I mentioned previously The high nickle content is only necessary when running temps close to or above 1000°C. No 2 stroke has those...

E.g. - 1.4301/1.4307 is great for cold forming, has a good weldability and will not get brittle while welding due to the low carbon content. The ductility of the stainless grades is better than for mild steel and yield strength over temp is also far better. A 2-stroke exhaust is not in a corrosive environment, the only thing that'll happen is hot gas corrosion which the mentioned stainless materials are also superior.

In the end no one is aiming for 200k km's or 3000 full thermal cycles so a lot of materials will work. Just do the best you can when rolling the parts and you don't even need a weld filler, if so choose the right one and you are good to go.

About 321, to my knowledge, it is simply a 304 stabilized with Ti against the intergranular corrosion risk. But indeed the Nickel content is slightly increased (from 8 to 9% min), frankly speaking I did not notice that. I don't know exactly why, because this is not highlighted in the various technical papers on it.

We use it in my company for oil refinery applications.

another small error has come up in my excel.

I've openend e new topic, as that will be easier to keep track of updates/corrections etc :

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Mr. Frits and Mr. Jan, or as far as you can tell, I do not recall seeing here specifically these Aprilia RSA 125 piston measurements and the material used

LeonardoMRF2 a écrit:

Mr. Frits and Mr. Jan, or as far as you can tell, I do not recall seeing here specifically these Aprilia RSA 125 piston measurements and the material used

That is not an Aprilia piston Leonardo. It belongs to a series of sketches showing my method of piston plugging.
The piston dimensions themselves are not relevant here.

I'm sorry Frits, I didn't explain, I used your drawing just to illustrate my question, what I want is the Aprilia RSA 125 piston dimensions, I want to compare with a reference that I use to size pistons

Hello frits,

I am interested to learn more about how to create a rain ignition mapping that works more softly and smoother in the beginnen of the resonance and torque area

Know your paper in german for kreidler and the advise to build a 100 percent throttle full power curve with your example on a rsa!

That works great in our hiro classic enduro with a hpi programmable ignition with switch for two curves :) :)

Now like to built one for wet and slippery conditions. Is the only thing to do, to reduce the pre ignition timing or are there other tricks and secrets !?

Do you have an example for a rain map from the rsa for us?


Thanks a lot ...to Mr. FritsTwo stroke

Viele grüße! Wolfgang

wos a écrit:

Hello frits, I am interested to learn more about how to create a rain ignition mapping that works more softly and smoother in the beginnen of the resonance and torque area
Know your paper in german for kreidler and the advise to build a 100 percent throttle full power curve with your example on a rsa! That works great in our hiro classic enduro with a hpi programmable ignition with switch for two curves :) :) Now like to built one for wet and slippery conditions. Is the only thing to do, to reduce the pre ignition timing or are there other tricks and secrets !?
Do you have an example for a rain map from the rsa for us?
Thanks a lot ...to Mr. FritsTwo stroke Viele grüße! Wolfgang

Hallo Wolfgang, what exactly should it do, this "ignition mapping that works more softly and smoother in the beginning of the resonance and torque area"? Reduce the power, or fill the 'hole' in the torque curve?
If your 'dry' ignition mapping is optimal, that hole will already be filled as much as possible, so the only remaining option for a 'rain' ignition would be to reduce the power and the only ways you can do that via the ignition is by giving it too much or too little advance, or by skipping sparks every xth revolution.
Below the power band there is already a lot of advance, as you will have seen in the 100% throttle mapping that you mentioned; even more advance might be harmful to the engine.
Reducing the advance will yield exhaust gases with more heat and more energy, which could aggravate the torque hole.
Summarizing: what you are looking for, is quite difficult to program in just an ignition map. You will need other inputs as well, from traction control or wheelie control sensors for example.
In the 1970s I built 'rain pipes' with somewhat narrower headers, shallower cones and bigger end cone restrictor diameters. They worked fine, but they had to be fitted before the race, while you are probable looking for different settings that can be selected by just switching them on or off during a race...

There were no 'rain maps' for the RSA. There was a threedimensional engine control map with inputs from engine rpm, throttle position, exhaust gas temperature and detonation sensor signals, and with outputs controlling the ignition timing, the position of the two-stage exhaust power valve, and the pulsating frequency of the fuel power jet. It took a lot of time and work to compose it...

besides the ignition :
ride in one gear lower than in the dry. it's best to ride in an rpm higher than max torque : when traction brakes, rpm rises quickly, but because your rpm is already higher than rpm of max torque, with the increase of rpm LESS torque will be send to the wheel which automaticly tends to reduce the slipping wheel.
lot's of people ride in a lower rpm than normaly in the dry, but when traction brakes than, with the increase of rpm, more torque is send to the rear wheel, increasing the wheel slip

Hi frits, hello jan :)

Thanks to you!

there is nearly no hole before the beginning of the resonance. ..no need to force the pipe with extra high pre ignition. cause of its lenth we use only 23' pre ignition

just want to soften The very straight up rising of the torque

Yesterday i joked with my fellow. ..let us build a exhaust valve System :)

jan? Seems you also have some cross or enduro experiences? :) thank you! Surely that helps...but as a additional Electronic goody...try to become more modern...like to add a rain map :)

what a pitty! we have no additional sensors...but in fact of that ...not that much work you had frits

you are right frits...like just to switch ....impossible to change a pipe during a 6 hour lasting enduro race...further an enduro trac provides many diffrent types of surfaces. ..rock...gravel ...sand...mudd or slippery roots of trees...

Our custom pipe has a narrow difusor and header... based on your fos formula frits...it is peaking at 8500...about 1100 mm length... done our best for a wide powerband

and converted the h.i.s system of hiro to an ordinary reed valve system like on the cr 125 elsinore that gave us additional torque at low reves...

maybe we should reduce compression ratio and squish a little bit to shift and flaten the torque peak...gaining a bit more overrev

to skip some sparks is not possible in the hpi...only as a limiter function at high rev

And i will surely start some experiments reduce the advance timing. ..maybe to 17...15' ...or do a kind of pwm modulation in the interested area of the curve...

Have a nice day!... with two strokes! :)

Viele Grüße to you!

Wolfgang