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

Not at those rpm. I also tried 37°, 33°, 30° and 27° by the way.

edit: I also tried the smaller reed valve and thinner reed plates, it didn't help.

Daniel A. a écrit:

Frits, do you think I should try a 19 or 20mm restrictor instead of 18mm?

18 mm is near the limit for your 28 rearwheel-horsepower. But going larger is safe, so you can give it a try.
And make sure that everything downstream of the restrictor is wide enough. 20% more diameter than the restrictor itself should be OK.

Thanks for the fast response

Okay, I will try 19mm and hope that the maximum power doesn't drop too much.

After the restrictor there are ~5cm with 24mm diameter and then comes the silencer with 26mm diameter :) That shouldn't be the problem.

Thanks again!

Regards

Daniel A. a écrit:

Thanks for the fast response

Okay, I will try 19mm and hope that the maximum power doesn't drop too much.

After the restrictor there are ~5cm with 24mm diameter and then comes the silencer with 26mm diameter :) That shouldn't be the problem.

Thanks again!

Regards

I see you are with some difficults, 2 strokes can be quite tricky...

From previous experience of mine I thought that too, smaller restrictor gived more power.

From the last experience I had I am not so sure now, I thinks that there is a correct "range", and it would work more or less the egt build up in the pipe. But I don't have a dyno to confirm.

motoholic71 a écrit:

Yep that little engine would not be in "shame" at a race track,even the chrome bores were somewhat uncomun on a street bike back then.

I recall Reading about a SP version with 34 carbs etc any one knows or I'm just dreaming?

PS just to close this the kr1 was the fastest 250 of 4 (nsr,rgv,tzr) and held speed record for 250 production machine at Bonneville.The Kr1-r had 35mm carbs and a close ratio box to compete in SP and seems that a full F3 kitted bike puts out 68HP!!

OK I'm out

Hello Motoholic71
The KR1, KR1S and KR1SP were all sold in New Zealand primarily as 250cc production racing bikes as this class was extremely popular and competitive. Simon Crafar won the 88 250 production title on the KR1 although he was clearly down on speed compared to the late arriving RGV250J. The New Zealand market version Honda NSR250 of 1990 was quicker again and was the machine that beat all others including KR1S, RGV250L and the awful reverse cylinder TZR250. Kawasaki had another crack the following year supplying a New Zealand only model KR1SP but by this time the RGV250M/N had arrived and was in the hands of Brett Richmond who won every race of the season (I dont think he raced the final round as he had already won?). There were only ever enough KR1SP supplied to meet the homologation requirment for NZ 250 production racing, I have not seen one for many years
Cheers
Kel

Daniel A. a écrit:

Thanks for the fast response

Okay, I will try 19mm and hope that the maximum power doesn't drop too much.

After the restrictor there are ~5cm with 24mm diameter and then comes the silencer with 26mm diameter :) That shouldn't be the problem.

Thanks again!

Regards

remember to check for welds protruding into your smallest diameter section

kel a écrit:

motoholic71 a écrit:

Yep that little engine would not be in "shame" at a race track,even the chrome bores were somewhat uncomun on a street bike back then.

I recall Reading about a SP version with 34 carbs etc any one knows or I'm just dreaming?

PS just to close this the kr1 was the fastest 250 of 4 (nsr,rgv,tzr) and held speed record for 250 production machine at Bonneville.The Kr1-r had 35mm carbs and a close ratio box to compete in SP and seems that a full F3 kitted bike puts out 68HP!!

OK I'm out

Hello Motoholic71
The KR1, KR1S and KR1SP were all sold in New Zealand primarily as 250cc production racing bikes as this class was extremely popular and competitive. Simon Crafar won the 88 250 production title on the KR1 although he was clearly down on speed compared to the late arriving RGV250J. The New Zealand market version Honda NSR250 of 1990 was quicker again and was the machine that beat all others including KR1S, RGV250L and the awful reverse cylinder TZR250. Kawasaki had another crack the following year supplying a New Zealand only model KR1SP but by this time the RGV250M/N had arrived and was in the hands of Brett Richmond who won every race of the season (I dont think he raced the final round as he had already won?). There were only ever enough KR1SP supplied to meet the homologation requirment for NZ 250 production racing, I have not seen one for many years
Cheers
Kel

Thank you very much Kel,I find this events very interesting and it's a pleasure to read about them.

Why Kawasaki didn't continue and built a vtwin it's what I don't understand,they clearly could have and would have given then bases for at least another decade of development and who knows a racer.
Oh well

kel a écrit:

Kawasaki had another crack the following year supplying a New Zealand only model KR1SP but by this time the RGV250M/N had arrived and was in the hands of Brett Richmond who won every race of the season (I dont think he raced the final round as he had already won?). There were only ever enough KR1SP supplied to meet the homologation requirment for NZ 250 production racing, I have not seen one for many years
Cheers
Kel

I don't know if any ever came to Australia, I never heard of them. The class was of course also very popular west of the Tasman, won by such as Mladin, Corser, McCoy, West... but by the end 1991 it was a effectively single-make series, anyone who turned up on something other than an RGV was a curiosity (until the Aprilias arrived).

I had both an L and an M, as road bikes. The L performed the traditional power valve to piston seize, the M seized the day I sold it. I agreed to repair it on a shared cost basis, and discovered it had been running on steel re-sleaved cylinders. So in the end, the buyer had a bike that ran much better than it ever did for me

While the L had some rather nasty head-shaking tendancies, the M was possibly the most fun road bike I've ever owned for zipping up a twisty road and putting big 4-strokes in their place :)

GrahamB a écrit:

I don't know if any ever came to Australia, I never heard of them. The class was of course also very popular west of the Tasman, won by such as Mladin, Corser, McCoy, West... but by the end 1991 it was a effectively single-make series, anyone who turned up on something other than an RGV was a curiosity (until the Aprilias arrived).

Except in 90 and 91 when Fred Bayens finished second and then won the title on a NSR 250. I can remember when 50 riders would turn up for 30 places on the grid.

To Jan Frits ans others two stroke engine specialist I would have your point of view about this prepared bottom end , this is RD 500 engine and one bank cylinder has cranckase intake and the other one has piston skirt intake , do you think gas will go faster through transfert with enclosed conrod?, is there a problem of cooling it ?
What gain ? What risks?
Thanks for keeping sharing your knoledge.
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Motors31 a écrit:

...this is RD 500 engine and one bank cylinder has cranckase intake and the other one has piston skirt intake , do you think gas will go faster through transfert with enclosed conrod?, is there a problem of cooling it ? What gain ? What risks? [Vous devez être inscrit et connecté pour voir ce lien]

I think the RD500 is the ugliest two-stroke engine Yamaha ever built. Two completely different sets of cylinders (cylinder reeds versus crankcase reeds), hooked inlet tracts......
I will admit that the cases in your picture are beautifully made but I fear that the shrouded big end bearings will not live forever unless the crankshafts are converted to pressurized lubrication.

Sorry Gents,

Isn't this nr 3 off this beautyful topic?

Sander

It is!

Hi Guys

Does anyone have a view (or an accurate knowledge!) of the maximum possible width of a racing 2-stroke exhaust port (this is a non-bridged arrangement with exhaust sub-ports) in a cylinder using a single ring piston with pegged ring position.

I'm reffering specifically to a 68mm bore.

Is it an angular measurement for all bore sizes?
Is it a decreasing angular measurement as bore size increases?

I'm thinking about piston/ring wear, the possibility of the piston contacting the top of the port and of course reliability.

Best Regards

Ian

Here you go, Ian: [Vous devez être inscrit et connecté pour voir ce lien]

Hi Frits,

Many thanks for the link. Just to check I have it right 70% of . . . . . . bore diameter?

In my case 68.00 x 70% = 47.6mm

In the case of the Aprilia 125, 54.00 x 70% = 37.8mm

I presume chordal width?

Thanks for your input.

Best Regards

Ian

You're welcome, Ian. Yes, that's a chordal width of 70% of bore diameter.

Hello everyone!

I briefly said hello a few pages back. I'm Dan, I'm 24 and I'm studying for a PhD in mechanical engineering at the University of Bristol in England. Specifically I am working on a technology called 'ice pigging' in the process engineering sector. It's an innovative method of cleaning pipes and ducts without the need for dis-assembly. The video below explains more:

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

I just thought I would give my background before asking the following questions.

I am trying to develop a yamaha tzr 250 3xv v-twin. There are a couple of things in the design of the engine that I am pondering on trying to improve so thought this the best place to ask. Any help, opinions, advice is appreciated greatly :-) So thank you in advance.

The inner transfer duct wall on a standard 3xv-10 (91-92 SP) cylinder does not continue from the base of the cylinder wall to the port window. There is an abrupt step where the barrel spigot has been machined in order for the cylinder to fit in the crankcases. The picture below shows what I mean:

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

I think I should fill that area in (shown by the crude black lines) in order to provide a continual inner transfer wall from the base of the cylinder to the port window. This theory has been reinforced after reading some of the very useful information in these threads and also further readings into the coanda effect. Surely an abrupt step there could possibly detach the transfer flow from the inner wall? Do people think I should fill that area in? I would love to do a back to back on the dyno with and without the modification but cylinders are scarce these days.

Interestingly in the TZ 250 3yl/4dp/4tw etc. yamaha designed this area slightly differently without such a step:

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

I think I should copy the above layout. I can only assume that Yamaha didn't do this on the road going 3xv (very similar engine, only small differences) due to mass production reasons etc. Unless people think that the step might be there for a reason?

Another thing I would like to ask about is regarding the rear cylinder legs:

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

The above photo shows one of my cylinders sat in the crankcase looking at the where the reed valve mounts. As you can see the rear legs are quite chunky. The passage through to the transfer tunnels is quite small. The TZ cylinders shown above have much shorter legs and a much better flow path through to the transfer tunnels. I think there is scope to cut the legs back and copy the TZ style legs to a degree. Piston support will still be ample I am sure.

Thank you anyone for taking the time to read my ramblings and if anyone requires more info about the engine design please ask and I will be more than happy to oblige!

Best regards,

Dan

maccas a écrit:

Hello everyone!

I briefly said hello a few pages back. I'm Dan, I'm 24 and I'm studying for a PhD in mechanical engineering at the University of Bristol in England. Specifically I am working on a technology called 'ice pigging' in the process engineering sector. It's an innovative method of cleaning pipes and ducts without the need for dis-assembly. The video below explains more:

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

I just thought I would give my background before asking the following questions.

I am trying to develop a yamaha tzr 250 3xv v-twin. There are a couple of things in the design of the engine that I am pondering on trying to improve so thought this the best place to ask. Any help, opinions, advice is appreciated greatly :-) So thank you in advance.

The inner transfer duct wall on a standard 3xv-10 (91-92 SP) cylinder does not continue from the base of the cylinder wall to the port window. There is an abrupt step where the barrel spigot has been machined in order for the cylinder to fit in the crankcases. The picture below shows what I mean:

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

I think I should fill that area in (shown by the crude black lines) in order to provide a continual inner transfer wall from the base of the cylinder to the port window. This theory has been reinforced after reading some of the very useful information in these threads and also further readings into the coanda effect. Surely an abrupt step there could possibly detach the transfer flow from the inner wall? Do people think I should fill that area in? I would love to do a back to back on the dyno with and without the modification but cylinders are scarce these days.

Interestingly in the TZ 250 3yl/4dp/4tw etc. yamaha designed this area slightly differently without such a step:

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

I think I should copy the above layout. I can only assume that Yamaha didn't do this on the road going 3xv (very similar engine, only small differences) due to mass production reasons etc. Unless people think that the step might be there for a reason?

Another thing I would like to ask about is regarding the rear cylinder legs:

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

The above photo shows one of my cylinders sat in the crankcase looking at the where the reed valve mounts. As you can see the rear legs are quite chunky. The passage through to the transfer tunnels is quite small. The TZ cylinders shown above have much shorter legs and a much better flow path through to the transfer tunnels. I think there is scope to cut the legs back and copy the TZ style legs to a degree. Piston support will still be ample I am sure.

Thank you anyone for taking the time to read my ramblings and if anyone requires more info about the engine design please ask and I will be more than happy to oblige!

Best regards,

Dan

Taking off those 'legs' will certainly improve performance!
And filling that step in the transfer duct is a good thing too!
It is there for no good reason.

Jan,

Thank you very much for your reply. I really appreciate it. I will come back here once I have some results.

Best regards,

Dan

Hi all,

I want to tell you some news about my 80cm³ engine. As I already said I tried 30° and even 40° ignition advance + boost bottle and I couldn't get the stutter away. I also expanded the restrictor diameter to 19,5mm and it neither made the engine run smoothly.

But on the dyno I saw a big improvement and it is a lot easier now to rev over this critical area. The lowest power value raised from 1hp to 4hp at around 8000 rpm.

My ignitech is working again, too and the engine has a very nice power band now! It is usable from 9000 to 14500 rpm. I will show you a picture later. But I think the exhaust is really a bit too short, as Jan Schäffer already said.

One question to wax, because I still haven't understood: In which direction must the peak of the spark plug electrode show, to get this improvement that you noticed? Exhaust, opposite of exhaust or one of the both sides?

Regards,
Daniel

You had the side electrode towards the boost port. So the open side of the plug was towards the exhaust

Okay thank you! The term "side electrode" instead of electrode confused me But your second sentence is clearly.

Do you see a reason for this improvement?

If I had to guess, I would have said that the open side of the plug was aimed towards the boost port, because the fresh charge is coming from this direction and might reach the spark gap easier than the other way around. But obviously this can't be the reason, because you said you aimed the open side to the exhaust port.

Maybe the combustion center is a bit closer to the exhaust port with the open side aiming towards the exhaust, which leads to a higher exhaust gas energy and at the end to more maximum rpm?

Just my thoughts.

Regards,
Daniel

I always put it down to less fouling of the plug, but I have no real hard eveidence to support it. Only that it works. Try it yourself you will be suprised

Here is the promised photo. Nice to see the difference between static ignition and variable ignition :)

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

The stutter is not a problem anymore. It's still there but you can live with it. Thanks for all the hints!

I will try to remove the wave at ~10500 with different exhaust dimensions now.

Frits, what do you think, is my current exhaust too short or is it okay? Ignition at max torque (12200rpm) is 25° before tdc. Considering that you once told, ignition advance at max torque should be around 14° I would conclude, that my exhaust is actually too short.

Regards,
Daniel