[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)

t0nix a écrit:

Frits Overmars a écrit:

t0nix a écrit:

Hi, anyone knows anything about the technique aprilia instead of 'crankshaft and countershaft?

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very thanks Frits, but i search the design technique.

The design techniques are unpublished. You'll find the results of the design techniques if you study the manuals:
"http://www.serviceaprilia.com/public/racing/Index.asp?SubPath1=02_Parts and Manuals/02_2-stroke"
(remove the quotes before entering the above link).

/quote]You can sink the top (and bottom) edges of these ports, from zero at the corners to maybe 0,1 mm in the middle, depending on the port widths, while still maintaining sharp edges.
The sinking will spare the piston ring while the sharp top edges will hinder flow from the cylinder into the transfers.[/quote]
Hi Frits, what's the correct way to sink them?
making a little chamfer or a radius?
Thanks

Filandro a écrit:

Citation :

You can sink the top (and bottom) edges of these ports, from zero at the corners to maybe 0,1 mm in the middle, depending on the port widths, while still maintaining sharp edges.

Hi Frits, what's the correct way to sink them? making a little chamfer or a radius?

Take a guess .

Frits Overmars a écrit:

Filandro a écrit:

Citation :

You can sink the top (and bottom) edges of these ports, from zero at the corners to maybe 0,1 mm in the middle, depending on the port widths, while still maintaining sharp edges.

Hi Frits, what's the correct way to sink them? making a little chamfer or a radius?

Take a guess .

A 0.1 mm radius??
What's your real work, brain surgeon??
Jan, some pages ago, told us to use dental burrs, now we have all the infos about how to de-burr ports in the proper way.
Thanks

GrahamB a écrit:

It means that your motor will break, as you'd expect from hammering the piston against the head 200 times / second.

thanks

and the latest shape on the RSA was this?

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is this the best shape vor a high end 2 stroke engine?

thanks Manuel

Manuel Rainer a écrit:

is this the best shape vor a high end 2 stroke engine?

As far as I know now: yes.

Frits,

The cylinder head design above,would it be possible to adapt that to a flat top tz250 piston?

The tz has the small chamfer on the outer edge, would you cut that section in the head to be parallel to the chamfer on the piston?

Would the flat section of the head then be parallel to the piston also?

If you wanted to reduce the head volume (for leaded fuel), would you reduce the depth or the diameter of the combustion chamber?

Thank you very much

Michael

michaelten a écrit:

Frits, The cylinder head design above,would it be possible to adapt that to a flat top tz250 piston?

Sure,why not?

Citation :

The tz has the small chamfer on the outer edge, would you cut that section in the head to be parallel to the chamfer on the piston?

Yes.

Citation :

Would the flat section of the head then be parallel to the piston also?

Yes.

Citation :

If you wanted to reduce the head volume (for leaded fuel), would you reduce the depth or the diameter of the combustion chamber?

I certainly would not want to use leaded fuel. It is toxic, it is illegal in most forms of motorsport, and it has a lower flame speed and a lower energy content than regular gasoline. But if you insist: I would keep the same squish band width and reduce the depth.

Frits Overmars a écrit:

I certainly would not want to use unleaded fuel. It is toxic,

Frits, did you mean to say *leaded* ?

GrahamB a écrit:

Frits Overmars a écrit:

I certainly would not want to use unleaded fuel. It is toxic,

Frits, did you mean to say *leaded* ?

Yes Graham; thanks for that.
I have rectified the error in my previous post now. And to avoid any misunderstandings: I hate leaded fuel.

Except the toxicicity and the low flame speend and energy , are there any others reasons why you hate it?
I ask this question because your opinion doesn't seem to be the most popular one.

rosenoire a écrit:

Except the toxicicity and the low flame speend and energy , are there any others reasons why you hate it?
I ask this question because your opinion doesn't seem to be the most popular one.

If his opinion isn't the more popular here than who is?

Jan will probably came here and say the same thing about leaded fuel.

Thank you for the response Frits.

As far as the fuel. Leaded is not illegal to use here in Australia. According to the rules my options are 98 pump fuel or Avgas.

Surely Avgas is the better of these two options?

Michael

michaelten a écrit:

Leaded is not illegal to use here in Australia. According to the rules my options are 98 pump fuel or Avgas. Surely Avgas is the better of these two options?

Only if you have detonation problems. But even then, using Avgas is curing the symptoms rather than the disease.

Frits Overmars a écrit:

michaelten a écrit:

Leaded is not illegal to use here in Australia. According to the rules my options are 98 pump fuel or Avgas. Surely Avgas is the better of these two options?

Only if you have detonation problems. But even then, using Avgas is curing the symptoms rather than the disease.

Frits,

So you are saying you can make the same power with both the 98 pump fuel and Avgas?

Will the tuning window will be much larger with the Avgas though, over the 98?

As far as set-up between the two fuels. I have been told a head volume of 8cc (upside down, spark plug in) and a squish of 0.7mm for the Avgas.

Would you agree with the above for Avgas?

What would you suggest for head volume and squish for pump fuel?

The bike is a 2001 TZ250 5KE.

Thanks very much for your responses Frits, I really appreciate it.

Michael

michaelten a écrit:

Frits, So you are saying you can make the same power with both the 98 pump fuel and Avgas? Will the tuning window be much larger with the Avgas though, over the 98?

What makes you think the tuning window as you call it, will be larger at all with Avgas? All you'll get is a larger error window for blowdown time.area, ignition, jetting and cooling. But you'd better solve such problems instead of 'drowning' them in Avgas.

Citation :

I have been told a head volume of 8cc (upside down, spark plug in) and a squish of 0.7mm for the Avgas. What would you agree with the above for Avgas?

I have no TZ250 piston data at hand, so I have no idea what 8cc, upside down, spark plug in, means in terms of combustion chamber volume.

Citation :

What would you suggest for head volume and squish for pump fuel?

Same here; I have no idea what your kind of head volume ought to be. Let us say that a compression ratio of 14:1 and a squish gap of 0.6 to 0.7 mm are OK.
Do not think that higher ratios always give more power; maybe quite the contrary. Higher compression ratios do give a more vulnerable engine: more sensitive to ignition spark strength and piston ring wear. And it will rev less freely, which makes riding more difficult.

michaelten a écrit:

As far as set-up between the two fuels. I have been told a head volume of 8cc (upside down, spark plug in) and a squish of 0.7mm for the Avgas.

That's essentially what I used in my '93 model, with no problems. I usually ended up at 0.65 due to what base gaskets and cylinders I had.

I never tried avgas in the 5KE. I couldn't afford ELF MITS, so I tried various dodgy things (Shell optimax 100+ 20% toluene*, for example), but eventually settled on using the FIM standard rally car fuel (from Shell as it happened). Being formulated for turbos it has more detonation resistance and lower burn-speed than normally aspirated 4-stroke race fuel, and is about 30% of the cost of MITS.

Otoh, I also had a crack in my ecu from a crash by the previous owner, which generated lots of interesting intermittant faults that helpful people identified as everything else. Eventually I bit the bullet to buy a new kit ecu and it fixed it.

(*) Toluene is also carcinogenic, but according to Shell tech services, there is already 10-30% in their fuels as an octane booster depending on the fuel stocks of the moment. Also note that if you are using a fuel that contains ethanol (Optimax 100), it will tend to mask detonation from your det-counter rather than prevent it, and that the combination of ethanol and toluene will dissolve almost all known plastics, fuel-lines, o-rings, even the epoxy used for making CF fuel tanks...

Hi Guys

In superkart fibreglass fuel tanks they have had to change to Vinyl Esther resin as the quantity of Ethanol has increased in fuels. In fact more and more are favouring aluminium.

Ethanol now stands around 5% in most 99 octane road fuels (Shell V-Power, etc).

Of cousre Ethanol goes hand-in-hand with oxygen, so this level is also rising now in road fuels.

We in the UK use (by regulation) 102 Octane unleaded race fuel in out twins (Elf SK35 or Carless Hyperflo 250) and we use Avgas 100LL in our engines for Australia.

We have seen a slight advantage in power with theSK 35, but the Avgas is so forgiving with regards to jetting and detonation (we never see any). You have to do something really wild to seize on Avgas.

Here's a pair of pistons running nicely on Avgas 100LL mixed with Castrol A747.
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Frits,

With tuning window i mean with Avgas you can make a fairly big jetting mistake and it wont seize, just be low on power. Unfortunately I am not Erv Kanemoto, Avgas allows me to make jetting mistakes without it costing me too much in engine damage. Call it an insurance policy!

My understanding of unleaded, and especially low octane unleaded, is that if you get the jetting slightly wrong it will seize. Am I incorrect in thinking this?

Michael

I see, Michael. Your so-called tuning window is my so-called error window .
The importance of octane rating for two-stroke racing fuels is, and has always been, grossly overrated.
Twenty years ago when fuel specs were much more liberal than they are now, everybody was using Bluegas, usually ELF 124. Jan Thiel and I even used ELF 130. Those fuels had a both a high octane rating and a high energy content. The downside was poor flame speed and poor ignitability, worsened by the fact that these fuels not only permitted but even required a high compression ratio in order to extract that energy.
Then Shell brought out a racing fuel with an octane rating of 104. It did not require a high compression ratio, it was far less demanding on the ignition system and flame speed was much better, resulting in a cooler running engine with more overrev, which made riding it much easier. Many tuners do not realize the importance of this last point, but every rider will understand immediately.
Regarding your remark about seizures: if an engine is thermally sound, you can lean the mixture until the power drops, without any risk of seizing it. That goes for unleaded gas as well as for aviation gasoline.

Frits, a question: you mentioned slow flame vel. & high comp ratio being required. The high comp, thus low volume, has to do with the flame front reaching quicker the end gases? Or is it about the fuel needing to be compressed higher, in order to release the energy?

p.s. hope my question is not the one-page-answer type. nevermind if it is, I was just curious.

Vagelis a écrit:

Frits, a question: you mentioned slow flame vel. & high comp ratio being required. The high comp, thus low volume, has to do with the flame front reaching quicker the end gases? Or is it about the fuel needing to be compressed higher, in order to release the energy?
p.s. hope my question is not the one-page-answer type.

Thanks for your PS, Vagelis. You clearly understand the burden of answering forum questions .
This time the answer can be short: that fuel needed a large expansion factor in order to release its energy.

Frits Overmars a écrit:

Regarding your remark about seizures: if an engine is thermally sound, you can lean the mixture until the power drops, without any risk of seizing it. That goes for unleaded gas as well as for aviation gasoline.

What exacly you mean by Thermally sound engine?

An engine were the temperatures of all components and lubricants are always kept within safe limits.
By today's standards an aircooled engine cannot be powerful and thermally sound at the same time,
with the exception of small-capacity methanol-burning model engines.

Did you use some superbenzene additive to boost the octane for commercial gases(cheaper)? , it's not trackable on spectro analysers...I know that was used by a DTM team [Vous devez être inscrit et connecté pour voir cette image]