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

SEB4LO a écrit:

looks a bit like a go boom fast design

Definitive design

So what are the minimums I should be using? I came up with those looking at the prints and pics of the RSA. Appreciate your help.

Also for reference the cylinder bore shell and port extrusions into the cylinder are smaller than the actual bore of the engine so they will look closer than what they are. The second picture might look better?

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hello at all.

Jan or Frits can i ask you some questions?

can you post an draving or a image how was cutet the last version off the rotary valve in the RSA engine? and what were the opening end closing angles (starte openig, full opent, starte closing, full closed).

what was the balance factor of the RSA crankshaft and did you tried some different factors?

many thanks Manuel

Timing: 146°/93°

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Quelques images inédites:

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fpayart a écrit:

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Thanks

the holes on the piston, are through???

No,no this is just done to reduce the weight, above the piston pin because of the forged piston

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fpayart a écrit:

No,no this is just done to reduce the weight, above the piston pin because of the forged piston

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thanks

fpayart a écrit:

Timing: 146°/93°

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Thanks payart

93° after TDC ist full closet?
146° is before TDC and full open?

manuel

Correct

Manuel Rainer a écrit:

fpayart a écrit:

Timing: 146°/93°

93° after TDC ist full closet? 146° is before TDC and full open?

fpayart a écrit:

Correct

Fully open at 146° before TDC?
That would imply that the inlet port starts to open at about 30° before Bottom Dead Center....

93° after TDC ist full closed? 146° is before TDC and full open? Beginning opening

Those numbers are almost identical to my engine that uses 34 mm carbs. Ideal timing is 95-150. 100-150 actually makes more power but struggles to come of idle.

Howard:
Is your timing (95-150) using your dual disk valve setup or just with the single valve?

Fully closed 93° after TDC, wow, I did not think that it would be so late.

Why is everyone using around ~160° timing on a port-controlled engine then?
Looking at the timing of a rotary valve over 180° timing should theoretically even work better!? But I think practically it won't.

Somebody knows why? I haven't tested such huge timings until now.

Regards

PVO a écrit:

Also for reference the cylinder bore shell and port extrusions into the cylinder are smaller than the actual bore of the engine so they will look closer than what they are. The second picture might look better?

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Yes , second pictures looks better and numbers are finally ok

My engine uses a single disc but it has a second disc with holes that match the ports. It rotates about 25 degrees actuated by a cam. I can rotate the disc with the holes to full advance which now closes the port at 70 degrees atdc. This greatly reduces the time it takes to coax the engine onto the powerband. I have it setup now with a choke cable.

Daniel A. a écrit:

Fully closed 93° after TDC, wow, I did not think that it would be so late.

Why is everyone using around ~160° timing on a port-controlled engine then?
Looking at the timing of a rotary valve over 180° timing should theoretically even work better!? But I think practically it won't.

Somebody knows why? I haven't tested such huge timings until now.

Regards

Hi everyone , my name is Mike Gifford (brother of Howard), I am 57 yrs. old and have been racing and building two strokes for over 30 yrs.... The reason that piston controlled inlets are not much more than 160 deg. is because on a piston skirt controlled inlet the timing is symmetrical , which means if the port opens 80 deg. btdc it will also close 80 deg. atdc.. Starting becomes increasingly difficult with closing timing later than 80 deg. atdc.. In the snowmobile race community with rotax rotary valve engines timings of opening 150 deg. btdc and closing 80 deg. atdc have been used since the 90s when carb size was restricted .. More intake timing yielded more power but the engines often would not start when required and many racers missed many heats and finals.. This is why Howard developed a variable timing setup for the rotary valve.. We can now set the closing timing where the most power is and with the variable plate reducing the closing timing for starting ; the motor fires up like a mild trail engine ...

Aah, thank you!

I knew that starting is difficult with such big timings, but I didn't knew that the rotary valves you are talking about are variable. Now it makes sense :) Thanks again.

Daniel A. a écrit:

Aah, thank you!

I knew that starting is difficult with such big timings, but I didn't knew that the rotary valves you are talking about are variable. Now it makes sense :) Thanks again.

The 150 btdc opening and 80 atdc closing timings were in use without the aid of any variable timing arrangement and was about the limit for starting these machines with a recoil pull rope.. In 1999 Rotax released a cylinder reed valve engine and all the other manufacurers competing used a case reed design. Our team is the only one using a rotary valve motor ... We are excited ... This premier form of snowmobile competition called Champ 440 is similar to motorcycle GP racing except that 2 strokes are still used...

fpayart a écrit:

93° after TDC ist full closed? 146° is before TDC and full open? Beginning opening

hello

i am driving a 125 ccm TM KV 95 rotary valve kart engine with 86°-160° timing made like this:

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and i also testet one like this:

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but it doesnt works reali well.

did you had different valve designes vor different temperatures (summer/winter)?

thanks

We tried angling the leading edge in both directions and also we tried a crescent shaped trailing edge. Our theory was it would open the port more rapidly but it did not prove advantageous. We always found best power was achieved with a leading edge and trailing edge intersecting the center of rotation. We use a bigger plate to center the ports on the motor. In order to run a bigger plate (171 mm dia), we developed a counterbalance system on the rv shaft that eliminates the vibration and thus the need for carbon fiber material. We also found the steel plate shows less wear on the aluminum than carbon fiber and is much more durable without any performance loss. Our best run to date was 135.4 HP (standard correction) at 10300 rpm. That compares to our best reed motor at 126 hp at 10100 rpm. The rotary has a lot more over rev power than the reed as well holding good torque to 10600. The reed gives up at around 10200 using the same head, pipes, ignition, carbs and port layout. Both the rotary and reed motors are 440 cc 65 mm bore 65.8 mm stroke so you can see why we are excited.

Many thanks to Jan ,Frits and all the other contributors on this forum. With what we have learned over the past few months we have gained almost 10HP and we are still learning and making gains.

Manuel we race snowmobiles so we really do not have a summer design. We dyno test in the summer but there is no difference except for correction factor and jetting.

Jan did you hard anodize the wear surfaces of the rotary valve cover and crankcase? It would seem that a hardened surface would wear less with carbon fiber since it is fairly abrasive but perhaps anodized aluminum and steel moving parts together are not a good match! We have experienced more wear on the motor than the cover. What is your experience or advise with this?

Manuel Rainer a écrit:

fpayart a écrit:

93° after TDC ist full closed? 146° is before TDC and full open? Beginning opening

hello

i am driving a 125 ccm TM KV 95 rotary valve kart engine with 86°-160° timing made like this:

and i also testet one like this:

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

but it doesnt works reali well.

did you had different valve designes vor different temperatures (summer/winter)?

thanks

This is because there's a big difference between your KV95 engine and the RSA. On the KV engine the inletport is above the rotary valve's centerline while on the RSA it's on the right side. The best flow with partial open carburator is by opening the inlet port from the bottom up. This is easily done on the RSA by having a disc as seen on picture. On the KV you need something like the "grinding" picture to get a similar result.