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

Frits Overmars a écrit:

The above collection should be sufficient to earn me a reserved place in an asylum, don't you think, Graham? .

Hopefully we'll be in the same one, should be fun

Have you already expanded on the secondary compression theory somewhere in these pages? I have known people who apparently believed that if the engine finished the race, then the CR wasn't high enough...

...but even the "reasonable" 16:1 -ish ratio of the RSA is pretty high by 4-stroke standards (outside speedway with 100% methanol), and I've never read of "corrected" CR for 4 stokes.

Frits Overmars a écrit:

Keeping your minimum speed high is the most important'.

An off-topic aside on this mathematically obvious but usually forgotten point: a few years back a cycling coach realised this and encouraged his riders to go "into the red" on short climbs in a time trial, even if it meant they were slower down the other side (it's even more obvious in cycling because of quadratic wind resistance). The traditional approach was equal effort everywhere, although I'm sure no rider was ever silly enough to follow that advice.

Unfortunately he'd also coached a certain Floyd Landis some years earlier, so he has now disappeared from the sport.

GrahamB a écrit:

Have you already expanded on the secondary compression theory somewhere in these pages?

I'm not sure. Too many forums... The idea is that a large expansion ratio takes away exhaust gas energy that could otherwise be more useful supercharging the cylinder, so the next bang will be bigger, and the bang after that bigger still, and... you'll get the picture.
A low secondary compression/expansion ratio provides for more exhaust gas energy; it also provides for a larger cylinder volume above the exhaust port so the exhaust pipe has an easier time shoving washed-through fresh charge back into the cylinder because the resulting cylinder pressure rise will be smaller.

Citation :

I've never read of "corrected" CR for 4 stokes.

This useless corrected CR concept should never have been introduced at all; neither for two-strokes nor four-strokes.

like already said it is a pleasure to read all the knowledge and experience. 

one more question though frits - do you think there is a point when crankcase volume will become too big? the whole let's call it "swing" could somehow get to inactive maybe? or would an infinite crankcase volume be the best?

i know bidalot and metrakit for example used 85mm conrods in their 50cc Derbi race engines to lower CV and they work pretty well. we tried those cylinders with a 90mm conrod by using a 5mm spacer and the engine gave less power. however, more parameters change with the conrod length - so a real test is hard to do.

koenich a écrit:

do you think there is a point when crankcase volume will become too big? the whole let's call it "swing" could somehow get to inactive maybe? or would an infinite crankcase volume be the best?

In theory it would be best to connect the transfer ports directly to the outside world. Then the engine could breathe cool mixture through short tracts with low dynamic flow resistance. Don't worry about the 'swing'; transfer tracts, cylinder volume and exhaust pipe form a compound Helmholtz resonator that will swing just fine without the crankcase attached.

When the crankcase volume gets really big, fuel may separate from the air. Direct injection would solve this, but for now the time available for direct injection in a competition engine is too short to form a homogeneous mixture.

I once made an experimental cylinder with carburators bolted left and right against it. But starting was a problem and lubricating the big end was an even bigger problem, so for practical reasons we still use the crankcase.

hello

a question to frits or jan.

how is the surface in an RSA engine? 

What I see on the pictures, is that the surface in the motor housing is smooth. it would  smoothed by hand after milling?

How shoult be the Surfaces in the exhaust channel in the cylinder?

And the carburetor has to be polished?

Thanks Manuel

Frits Overmars a écrit:

GrahamB a écrit:

Frits Overmars a écrit:

some people still think I'm crazy .

But Frits, you're sure that relates to crankcase volume?

'The part of the exhaust port area beneath the transfer port level is a waste of real estate'.

'A high secondary compression ratio improves power in a four-stroke;
in a two-stroke with an efficient exhaust system it is the other way around'.

My little experience already show a bit of that. Just looking at Honda cylinders and comp. used it makes it more or less clear :).

"Normal price" Con rod's and big end's usually don't like to rev hard much time

hey guys,

one more question to the experienced dyno users. lets say you have a new engine putted together and want to dyno test + tune it. What is your approach? Do you follow any thumb rule what is done first and how the parameters (jetting, ignition, combustion chamber, exhaust,...) are changed?

Or do you just go trough them step by step? Like first lean down, then get the ignition done, then test different combustion chamber and then get to work on the exhaust? This is how we do it but still you have the problem of checking if the another combustion chamber would have worked out better with 2° ignition shifting.

So I am looking more for a "design fo experiment" approach - but i am not sure if this works on a 2-stroke.

Manuel Rainer a écrit:

hello

a question to frits or jan.

how is the surface in an RSA engine? 

What I see on the pictures, is that the surface in the motor housing is smooth. it would  smoothed by hand after milling?

How shoult be the Surfaces in the exhaust channel in the cylinder?

And the carburetor has to be polished?

Thanks Manuel

 
Filing the cast surface gave some more power: 0,2-0,3HP.
Polishing makes no sense

koenich a écrit:

lets say you have a new engine put together and want to dyno test + tune it. What is your approach? Do you follow any thumb rule what is done first and how the parameters (jetting, ignition, combustion chamber, exhaust,...) are changed?

When a new engine is put together I first turn it over by hand to make sure every part moves freely. Then I start it, warm it up slowly and run it in. You can give a thermally sound nikasil-bore engine full throttle right away but I prefer to take it real easy; it is important that the piston ring gets to seat properly.
Then I rev it up high a couple of times to make sure that bearings and squish are all right.
Make sure that the mixture is rich and the ignition is not too early. Only now should you start measuring power. After the first measurement make the mixture even richer; once you are sure it is running too rich, you can go leaner in small steps.
Do the same with the ignition timing: retard it and take measurements. You may find that by retarding, the low rpm power will get worse, will high rpm power may improve. Then increase ignition advance in small steps and measure, but stop at the rpm where the later ignition timing gave better power; if you measure the whole rpm range with a lot of advance, you may lose the engine.
Overlaying the various power graphs will give you the information you need to compose a variable timing ignition curve.
During all the above measurements a thin layer of carbon coating has built up in the exhaust pipe, altering its thermal conduction properties. So now you can start all over again. And again. And again ;-) .

Jan Thiel a écrit:

Manuel Rainer a écrit:

hello

a question to frits or jan.

how is the surface in an RSA engine? 

What I see on the pictures, is that the surface in the motor housing is smooth. it would  smoothed by hand after milling?

How shoult be the Surfaces in the exhaust channel in the cylinder?

And the carburetor has to be polished?

Thanks Manuel

 
Filing the cast surface gave some more power: 0,2-0,3HP.
Polishing makes no sense

thanks Jan 

So should all the surfaces in the engine have the roughness as filed? 
but the carbs are polished. it has no sense to polish the carburetor?

thanks Manuel

Frits Overmars a écrit:

koenich a écrit:

lets say you have a new engine put together and want to dyno test + tune it. What is your approach? Do you follow any thumb rule what is done first and how the parameters (jetting, ignition, combustion chamber, exhaust,...) are changed?

So now you can start all over again. And again. And again ;-) .

Yep the 2-stroke is a sissy when it gets down to power ;-) 

So after all, how did u handle it at aprilia? Starting off with the new rsa engine, trying new parts on it and always try to find the best combination? Or if you had for example a good combustion chamber you sticked with it?

koenich a écrit:

Frits Overmars a écrit:

koenich a écrit:

lets say you have a new engine put together and want to dyno test + tune it. What is your approach? Do you follow any thumb rule what is done first and how the parameters (jetting, ignition, combustion chamber, exhaust,...) are changed?

So now you can start all over again. And again. And again ;-) .

Yep the 2-stroke is a sissy when it gets down to power ;-) 

So after all, how did u handle it at aprilia? Starting off with the new rsa engine, trying new parts on it and always try to find the best combination? Or if you had for example a good combustion chamber you sticked with it?

It depends a lot of what kind of new engine.
A new engine, for example an RSW, was run for 5 minutes at full throttle, and 10.000 rpm,
like with a new piston.
After that a full HP test was done.
 
A completely different thing, of course, is the first test of a newly designed engine!
Like the RSA
We ran it slowly for a couple of minutes, then we let it rev a bit more.
And then we took it apart to look at any abnormal things.
There was a slight oil leak, which was cured.
After that we tried for power.
Within 2 days it gave 52HP!

When looking for more HP always try to change one thing at a time.
As even changing only one thing usually changes several things!

koenich a écrit:

...trying new parts on it and always try to find the best combination?

Obviously.

Citation :

Or if you had for example a good combustion chamber you sticked with it?

Power readings will tell you whether a specific combustion chamber works good in a certain combination. But they will never tell you whether there may be an even better version, let alone what that better version would look like.
CFD (Computational Fluid Dynamics) programs can sometimes show you the way; they can also point you in a completely wrong direction....

shit in shit out without knowledge and experience for such programs i still prefer to rebuild stuff from this thread or my own ideas and dyno test.

Jan Thiel a écrit:

Manuel Rainer a écrit:

hello

a question to frits or jan.

how is the surface in an RSA engine? 

What I see on the pictures, is that the surface in the motor housing is smooth. it would  smoothed by hand after milling?

How shoult be the Surfaces in the exhaust channel in the cylinder?

And the carburetor has to be polished?

Thanks Manuel

 
Filing the cast surface gave some more power: 0,2-0,3HP.
Polishing makes no sense

hi Jan

normally I have grinded the surfaces with 240 sandpaper. is this too smooth?

thanks manuel

I did a google research in order to get as much knowledge I can from people that have master the 2stroke engine tuning science..
After reading the Pit-Lane forum pages and a Classic bike forum pages (but in Dutch language using translator) where Jan Thiel and Frits Overmars write, I came back with a few questions..

My location is in Brno Czech republic.
At the moment i am working on 2T Kart engines as a hobby and while helping two amaterur friends with their racing.
The reason I ask theese questions is to better understand things I read in the forum (even if they are foundamental to many of you), and to learn from your experiences where I can get a quality service for my kart engine parts and at what cost when i will need to.

In cylinder coating many kart racers say that they experience better performance from their engine if they had not Niquasil but Gilardin coating.. dont have experience to judge this but what is your experience?
Are there any different coating qualities/performance gains here and what is the best 2T coating?
Where is a good place in Europe to send cylinders for re-coating, what is the average time they need for this service and what is the cost?
Is there something that we have to be aware of while asking a new coating?

I have seen in companies that offer a Detonation ring on head and on cylinder.
It looks like a copper insert but i am not familiar with this.
What is the material they use?
Can someone explain how they do it, what is the benefits and other comments possitive or negative.
Where can I also get such a service?

I think i have the answer to this question, just want to be sure about it.
I have an engine that in track goes up to 14.000rpm. If i would like to have more rpm, is this related with:
Advance timing (retard)?
Other?

Many kart drivers they try to get the carburettor as close as possible into the reed cage..
Where this help ( more power) ?

Where can I buy good quality Reeds and what is better to use Carbon or other material and in what thickness?
Is it a good idea/safe to cut reeds from a big sheet and something I should be carefull of ?

At photos from Aprilia RSA or RSW piston, there is a line-groove with small holes in it, just below the piston ring on the exhaust side.
Why is that and where it helps ( cooling/power/weight/other) ?

In Karting we are not allowed to change anything on the exhaust but we can "play" with the endcan/silencer size length volume etc.
Can someone in short tell me abou it..
For example short with small diameter/low volume silencer will give more power/torque/move the power up/down other info etc...



somewhere i read... Jan Thiel said (after dorna stopped the 2T racing) that two stroke engines will survive now only in Kart racing but there will not be any develompnet due to the strict regulations...

Well i believe that this can be a nice challenge..
Try to figure out how to get better performance/more power from an engine while you have not fully freedom due to regulations.

At the moment the best known kart engine tuner is a French named Patric Sarvard (Tec-Sav).
Sarvard use to be a motorcycle mechanic in motoGP ELF bikes. Recently i read that his best 125cc kart engine was measured at 49.7HP...
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Frits Overmars a écrit:

'A high secondary compression ratio improves power in a four-stroke;
in a two-stroke with an efficient exhaust system it is the other way around'.

I am wondering where would you draw the line between a (too)high, and a suitable compression ratio in a two-stroke application? 11? 13? 15? Or in corrected values: about 6 / 7,5 / 9?

Haufen a écrit:

Frits Overmars a écrit:

'A high secondary compression ratio improves power in a four-stroke;
in a two-stroke with an efficient exhaust system it is the other way around'.

I am wondering where would you draw the line between a (too)high, and a suitable compression ratio in a two-stroke application? 11? 13? 15? Or in corrected values: about 6 / 7,5 / 9?

We are currently testing a geometrical ratio of 9:1. I do not want to have anything to do with 'corrected' compression ratios  .

Frits Overmars a écrit:

Haufen a écrit:

Frits Overmars a écrit:

'A high secondary compression ratio improves power in a four-stroke;
in a two-stroke with an efficient exhaust system it is the other way around'.

I am wondering where would you draw the line between a (too)high, and a suitable compression ratio in a two-stroke application? 11? 13? 15? Or in corrected values: about 6 / 7,5 / 9?

We are currently testing a geometrical ratio of 9:1. I do not want to have anything to do with 'corrected' compression ratios  .

Sorry, I forgot  

That sounds really low to me. May I ask for details of the engine, such as displacement, bmep and piston speed range?

vangelas a écrit:

I have seen in companies that offer a Detonation ring on head and on cylinder.
It looks like a copper insert but i am not familiar with this.

I think it is bronze. It is standard on some Yamaha engines, but usually it is used to repair a damaged head (or cylinder). I think the idea is that a material with very high heat conduction will prevent surface hot-spots that might contribute to triggering ignition under the squish-band. It seems optimistic to me, since it is more likely to be a hot-spot on the piston that is the problem... but that's just a guess.

GrahamB a écrit:

vangelas a écrit:

I have seen in companies that offer a Detonation ring on head and on cylinder.
It looks like a copper insert but i am not familiar with this.

I think it is bronze. It is standard on some Yamaha engines, but usually it is used to repair a damaged head (or cylinder). I think the idea is that a material with very high heat conduction will prevent surface hot-spots that might contribute to triggering ignition under the squish-band. It seems optimistic to me, since it is more likely to be a hot-spot on the piston that is the problem... but that's just a guess.

 
Yes, it is bronze.
It is mainly done to repair a cylinder damaged by detonation.
And to avoid having a radius on top of the bore, which causes detonation.

Haufen a écrit:

May I ask for details of the engine, such as displacement, bmep and piston speed range?

Of course you may. Displacement is 50 cc. I cannot answer the other questions at the moment, as it is a joint project.
Whereabouts in Germany do you live, Haufen? We will test the engine next sunday, 7 July, at the Oberlandring in Bernsgrün (http://simsongp.forumprofi.de/forum-anzeigen-termine-f7.html)

Thank you for the reply about the detonation ring.

Regarding the rest of my question, do someone know about and can share with me?
Here they are again..

In cylinder coating, is there any difference in performance by using instead of Niquasil ,Gilardin or other coating?
Can you please suggest where I can send my cylinders in Europe for repair that according to your experience they offer a good quality/fast service at good prices?
Is there something that I have to be aware of, while asking a new cylinder coating service ?

Can you also suggest a place that they offer a detonation ring insert service, just in case I might ever need it?

I have a 2T 125cc engine that during racing has a max. of 14.000rpm.
If i would like to gain/see more rpm, do I have to:
1. Retard the Advance timing?
2. Reduce the length of the exhaust?
3. Other?

When i will move the carburettor as close as possible into the reed cage, is this going to give me more torque, more power or move the power band...? Where this modification help?


Can you please suggest a good supplier, where i can buy Reeds and what is better to use Carbon or other material?
What exactly affect the reed thickness, and what thickness do you suggest?


I have seen photos from Aprilia RSA or RSW? piston. Thereis a line-groove with small holes in it, just below the piston ring on the exhaust side.
Why is that and where it helps ( cooling/power/weight/other) ?

How affects the engine characteristics the exhaust length and the end silencer sige/length/volume?


I know ,I have got many questions, maybe for some of you just fundamental... But I will very much appreciate if someone with more experience/knowledge will share with me...

Thank you!!!