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

{mRk} a écrit:

Thanks for the explanation.
I wanted a exhaust tuned to a lower revs. To improve the performance of the exhaust at high revs I wanted to vary the energy of the spark. This is a test I wanted to do. If I understand correctly, it is not recommended to do so.
For the TZ 250 used for the tests was made a new exhuast?

The idea is to extend the working range of the exhaust. For similar reasons I wanted to experiment with de Laval nozzles. I just got the tube 28x1 mm for changing the exhaust.

Ok I understand, changing the nozzles is a good idea it can change a lot.

Bob van der Zijden a écrit:

{mRk} a écrit:

In the link you can see the graph of the tests performed with a TZ 250:
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The green graph is the stock Yamaha TZ250 CDI.
The blue graph is the same bike with the CDI Zeeltronic PDCI-25V with spark energy (62 mJ) constant at all rpm.
The red graph is the same bike with the CDI Zeeltronic PDCI-25V with 50% spark energy (about 30 mJ) at 12000 rpm.

I have to run some test with the motor 125 by varying the energy of the spark. For this reason I'm interested in this argument. I hope to find the time to perform the tests, the CDI is ready and wired.

Comment

You mention the  amount of energy being 62 mJ. Is this a calculated value or a measured one and if so how was it measured.

Bob van der Zijden

I asked Borut, Mr. Zeeltronic, the data of the Zeeltronic unit that I use. In the fall I started comparisons between various Zeeltronic unit, including those with the ability to set different energy levels. But something did not work as I expected. I asked him to do some comparison tests in his laboratory. The spark energy level of my standard Zeeltronic unit is 62 mJ, constant at each revs. That's why I took this value as a reference. Keep the spark energy constant has been a project choice. Borut has performed the measurements in the lab and gave me back my electronics. I wanted to go back to comparison work.
But mine are electronic for single-cylinder engines.
Now I also asked the exact data of the PDCI-25V. Borut replied that the energy of electronic for two cylinder engines has a slightly lower value of my electronics, but always constant.

LucF a écrit:

{mRk} a écrit:

Thanks for the explanation.
I wanted a exhaust tuned to a lower revs. To improve the performance of the exhaust at high revs I wanted to vary the energy of the spark. This is a test I wanted to do. If I understand correctly, it is not recommended to do so.
For the TZ 250 used for the tests was made a new exhuast?

The idea is to extend the working range of the exhaust. For similar reasons I wanted to experiment with de Laval nozzles. I just got the tube 28x1 mm for changing the exhaust.

Ok I understand, changing the nozzles is a good idea it can change a lot.

Thanks for the advice. I'll try to dedicate myself first to the test with de Laval nozzles.

{mRk} a écrit:

LucF a écrit:

{mRk} a écrit:

Thanks for the explanation.
I wanted a exhaust tuned to a lower revs. To improve the performance of the exhaust at high revs I wanted to vary the energy of the spark. This is a test I wanted to do. If I understand correctly, it is not recommended to do so.
For the TZ 250 used for the tests was made a new exhuast?

The idea is to extend the working range of the exhaust. For similar reasons I wanted to experiment with de Laval nozzles. I just got the tube 28x1 mm for changing the exhaust.

Ok I understand, changing the nozzles is a good idea it can change a lot.

Thanks for the advice. I'll try to dedicate myself first to the test with de Laval nozzles.

Your problem might even be solved if using nozzles of about 20-21 mm in diameter.(unless you have more than 75hp)
That will also result in a strong rise of the temperature and also in power.

gr. Luc

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Not sure if this image uploaded or not.
First off I would like to introduce my self as I am a Pit-Lane virgin. My name is Jason Smith and I am from Ny Usa and am involved in snowmobile racing.
I have two questions for Jan or Frits or any one else's expert advice.
#1This cylinder is off of a Suzuki (Arctic-Cat) 440cc twin engine 66.5mm bore 63mm stroke. Its hard to see in the image but with the piston at BDC the top of the piston is actually 2mm above the floor of the transfers. Why would they do this straight from factory? I've heard things from aids in cooling piston, to helps attach the charge to piston? Also supposedly in the 70's they designed something similar? Any theory here?

question #2 This engine originally was designed for sno-cross racing 8500rpm, on and off throttle. With our form of racing we hope to increase RPM to 10-10500 for Ice oval sprint racing. Compared to other OEMs designs in its class our C port is gigantic. Should we attempt to weld or fill the C port in order to widen the B ports? Any advice would be greatly appreciated.
Thank you in advance

jasonsmithrealtor a écrit:

...with the piston at BDC the top of the piston is actually 2mm above the floor of the transfers. Why would they do this straight from factory? I've heard things from aids in cooling piston, to helps attach the charge to piston?

Lowering the port floors below BDC is bad for power and I cannot think of a sound reason to do so. Maybe the factory 'composed' this engine with existing parts from other models.
For good piston cooling you need the scavenging flow to cling to the piston and a piston edge protruding into the flow will kick the flow up, detaching it from the piston dome, even in the vicinity of BDC where the piston is 'at rest' for a while.

Citation :

This engine originally was designed for sno-cross racing 8500rpm, on and off throttle. With our form of racing we hope to increase RPM to 10-10500 for Ice oval sprint racing. Compared to other OEMs designs in its class our C port is gigantic. Should we attempt to weld or fill the C port in order to widen the B ports?

Before doing any welding you can enlarge the B-ports by narrowing the bridges between B- and C-port. It is much simpler than reworking a welded-up cylinder and it may show you the way to go; I would try that first.

hi

Frits. can you say yes or no. or maybe a short explanation if your time allows it.

Did a smaller squish area liken in the modern 125 6 speed karts has a variable exhaust temprature effect over the rpm range?

if yes, how it can only makes hotter exhaust gas temperatur in high rpm and how does it works that it doesnt make hotter gas in the low rpm?

Thanks a lot

Manuel

Manuel Rainer a écrit:

Did a smaller squish area liken in the modern 125 6 speed karts has a variable exhaust temprature effect over the rpm range. if yes, how it can only makes hotter exhaust gas temperatur in high rpm and how does it works that it doesnt make hotter gas in the low rpm?

The exhaust gas temperature is variable over the rpm range anyway, but that is not what you mean, is it?
Let's assume for a moment that combustion takes a fixed period of time. With a fixed ignition timing this will mean that the end of combustion, expressed in crank degrees, will become later as the revs go up. And this means: hotter exhaust gas by the time the exhaust ports open.
But the velocity with which the gas is squeezed from between piston and squish band also increases as the revs and the piston speed go up. This squish action speeds up combustion, counteracting the increased duration.
If you reduce the squish area, this counteraction is also reduced, mainly at high rpm where the squish action is strongest.

Jan & Frits, I have read where it was mentioned that the bent Vs straight pipe cost a little power & that the increased length of the stinger required with the bent pipe cost power also,

I wondered if this cost in stinger length may be reduced if it had a larger stinger , your thoughts please

Frits Overmars a écrit:

jasonsmithrealtor a écrit:

...with the piston at BDC the top of the piston is actually 2mm above the floor of the transfers. Why would they do this straight from factory? I've heard things from aids in cooling piston, to helps attach the charge to piston?

Lowering the port floors below BDC is bad for power and I cannot think of a sound reason to do so. Maybe the factory 'composed' this engine with existing parts from other models.
For good piston cooling you need the scavenging flow to cling to the piston and a piston edge protruding into the flow will kick the flow up, detaching it from the piston dome, even in the vicinity of BDC where the piston is 'at rest' for a while.

Citation :

This engine originally was designed for sno-cross racing 8500rpm, on and off throttle. With our form of racing we hope to increase RPM to 10-10500 for Ice oval sprint racing. Compared to other OEMs designs in its class our C port is gigantic. Should we attempt to weld or fill the C port in order to widen the B ports?

Before doing any welding you can enlarge the B-ports by narrowing the bridges between B- and C-port. It is much simpler than reworking a welded-up cylinder and it may show you the way to go; I would try that first.

Thank you Frits. The problem with widening the B port is our concern with snagging rings as that's where the piston ring locator pins are. We have repinned pistons in the past so the pin is located in center of the C port . However this was with a single ring piston. Running dual rings would be a nightmare trying to relocate pins accordingly. From my understanding 2 rings are better for transferring heat to the cylinder, but less drag with single rings. Any advice on single versus dual rings? Thanks in advance

jasonsmithrealtor a écrit:

From my understanding 2 rings are better for transferring heat to the cylinder, but less drag with single rings. Any advice on single versus dual rings?

Maybe piston rings transfer piston heat to the cylinder wall. But they certainly generate friction heat themselves.
For a race engine I would go for a single ring with the ring peg diametrically opposite the exhaust port.

Frits Overmars a écrit:

For a race engine I would go for a single ring with the ring peg diametrically opposite the exhaust port.

Ok Frits, but have you seen the great wide of the C-port in the darkness? In this case not a little to risky?

LucF a écrit:

Frits Overmars a écrit:

For a race engine I would go for a single ring with the ring peg diametrically opposite the exhaust port.

Ok Frits, but have you seen the great wide of the C-port in the darkness?  In this case not a little to risky?

It's difficult to judge the port width from the picture. As a guideline I can say that I have run the ring gap over the center of a 22 mm wide C-port  in a 54 mm bore cylinder without any problems. So you might say that as long as the port width is no more than 40% of the bore, it should be safe, provided of course that you use a good quality ring.

jasonsmithrealtor a écrit:

[Vous devez être inscrit et connecté pour voir cette image]

Not sure if this image uploaded or not.
First off I would like to introduce my self as I am a Pit-Lane virgin. My name is Jason Smith and I am from Ny Usa and am involved in snowmobile racing.
I have two questions for Jan or Frits or any one else's expert advice.
#1This cylinder is off of a Suzuki (Arctic-Cat) 440cc twin engine 66.5mm bore 63mm stroke. Its hard to see in the image but with the piston at BDC the top of the piston is actually 2mm above the floor of the transfers. Why would they do this straight from factory? I've heard things from aids in cooling piston, to helps attach the charge to piston? Also supposedly in the 70's they designed something similar? Any theory here?

question #2 This engine originally was designed for sno-cross racing 8500rpm, on and off throttle. With our form of racing we hope to increase RPM to 10-10500 for Ice oval sprint racing. Compared to other OEMs designs in its class our C port is gigantic. Should we attempt to weld or fill the C port in order to widen the B ports?  Any advice would be greatly appreciated.
Thank you in advance

Jason, May be the cylinder can be 2mm up?  It is much, but depends on the timings.
May be it is even necesary if you want have power at 10k

frits i think i found a problem. after only a few hours i see black in the transfer ports   


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SB07 a écrit:

I have a question for Mr. Frits

what is the function of this type of exhaust? what are the differences with the classical model? Thank you


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With this exhaust you have a wider power range but less torque and hp.
Perfect for fixed gear engine.

LucF a écrit:

jasonsmithrealtor a écrit:

[Vous devez être inscrit et connecté pour voir cette image]

Not sure if this image uploaded or not.
First off I would like to introduce my self as I am a Pit-Lane virgin. My name is Jason Smith and I am from Ny Usa and am involved in snowmobile racing.
I have two questions for Jan or Frits or any one else's expert advice.
#1This cylinder is off of a Suzuki (Arctic-Cat) 440cc twin engine 66.5mm bore 63mm stroke. Its hard to see in the image but with the piston at BDC the top of the piston is actually 2mm above the floor of the transfers. Why would they do this straight from factory? I've heard things from aids in cooling piston, to helps attach the charge to piston? Also supposedly in the 70's they designed something similar? Any theory here?

question #2 This engine originally was designed for sno-cross racing 8500rpm, on and off throttle. With our form of racing we hope to increase RPM to 10-10500 for Ice oval sprint racing. Compared to other OEMs designs in its class our C port is gigantic. Should we attempt to weld or fill the C port in order to widen the B ports?  Any advice would be greatly appreciated.

Thank you in advance

Jason, May be the cylinder can be 2mm up?  It is much, but depends on the timings.
May be it is even necesary if you want have power at 10k

Lucf, we are already decently timed i feel 200 exhaust and 130 transfer, we may consider lowering cylinder, then we would need to raise transfers and epoxy floor to match piston. I know we tried epoxying floors as is and flow went way down on flow bench.

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Here is a better image of C port

"Rough" measurements are 22mm width 66.5 mm bore

jasonsmithrealtor a écrit:

[Vous devez être inscrit et connecté pour voir ce lien]

Here is a better image of C port

"Rough" measurements are 22mm width 66.5 mm bore

What with the sky-high price for property in Beverly Hills ( or similar ) and related commissions, a few custom pistons shouldn't stretch the ol' budget all that much.

Personally, before spending new money, I'd probably machine the crowns, adjust CR using an old head, and run a quick test or two.

If there's a benefit discovered, then proceed with new parts.

Maybe ?

LucF a écrit:

jasonsmithrealtor a écrit:

Jason, May be the cylinder can be 2mm up?  It is much, but depends on the timings.
May be it is even necesary if you want have power at 10k

Lucf, we are already decently timed i feel 200 exhaust and 130 transfer, we may consider lowering cylinder, then we would need to raise transfers and epoxy floor to match piston. I know we tried epoxying floors as is and flow went way down on flow bench.

Ok Jason, than any lift up would be to much with 200 exhaust. I saw you already changed the B ports in the right way.
May I ask, can you to show us the powercurve before changing? The gain should be about 8 hp.

Frits Overmars a écrit:

Manuel Rainer a écrit:

Did a smaller squish area liken in the modern 125 6 speed karts has a variable exhaust temprature effect over the rpm range. if yes, how it can only makes hotter exhaust gas temperatur in high rpm and how does it works that it doesnt make hotter gas in the low rpm?

The exhaust gas temperature is variable over the rpm range anyway, but that is not what you mean, is it?
Let's assume for a moment that combustion takes a fixed period of time. With a fixed ignition timing this will mean that the end of combustion, expressed in crank degrees, will become later as the revs go up. And this means: hotter exhaust gas by the time the exhaust ports open.
But the velocity with which the gas is squeezed from between piston and squish band also increases as the revs and the piston speed go up. This squish action speeds up combustion, counteracting the increased duration.
If you reduce the squish area, this counteraction is also reduced, mainly at high rpm where the squish action is strongest.

yes Frits that is was what i meant. and thanks for the nice explanation.
so in the 125 kart engine there is made a compromise between the benefits of a squish band in combustion, but not to much to get the hotter exhaust gas in high revs.

thanks a lot

Manuel

Frits

how many was (on the rsa ), the clerance between the ring and his housing in the piston ??? 0,030MM,.....;more....., less.....
i know is very important on a 4 stroke engine hight speed turn ( blow-by, ect ....) but on a 2 stoke , i dont know the right value  

Frits a déjà répondu à cette question. C'est 0,04 de mémoire.

merci quiko
il me semble effectivement l avoir vu, mais je ne retrouve pas la page , et je ne sais plus si il ne parler pas du jeu a la coupe plutot....????