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Idea rotating inlet two stroke for smooth riding

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AlexS:
On the back thinking of an two stroke concept engine.

Always interested in 60s two multi cylinder stroke racers of Japan. For example Suzuki RK67 50cc twin cilinder disc valves with 14 gears. Or RP68 V3 cylinder with disc valves 19 hp 19.000 rpm.
http://www.classic50racingclub.co.uk/Suzuki-Works-50cc-Racing-Motorcycle/
Kawasaki I and II 125c 2 and 4 cylinders

Or the prototype square four 750 of Kawasaki https://www.motorcyclespecs.co.za/model/kawasaki/kawasaki_square_four.html



Have a chat with computers.

Rotary discs are back in the day connected directly to the crankshaft. Which result in fast speeding opening and closing time.

What if you let the disc rotate the half the speed of the crankshaft. You need than 2 cut outs at 180 degree phasing. But then you are able to make a banana or tear drop inlet cut out in the disc. Not for race engine, but let say commuting city driving. Smoother running and higher mid range torque. Accurate timing.

When the disc rotate slower and so need longer arch length cut out. Are you able to create an increasing opening area of the inlet port / disc. To gradually opening to reduce intake turbulence. Think of it like a cam lobe the port begins to open slowly, then more rapidly as the disc rotates.

Opening disc would be around 95 bTDC angle (47,5 degree rotary disc). And what I understand most transition. When you aim for torque you need to have a fully opened inlet port area when the piston is at TDC to 30 degrees aTDC. Closing starting at 5 degrees (55 degrees) for fully closed (60 degrees). And closing need also more smooth and not abrupt shutting off. there for the inlet port is eclipse formed and the cut out of the disc has a radius of 3-5 mm.

Looking at disc, might looking at airplane wings.
Opening. The leading edge of the cutout is curved or sloped, starting shallow and deepening gradually.
Closing. The trailing edge of the cutout is less steep, extending the closing point. A gentle taper or rounded edge to avoid sudden cutoff of flow.

Only thing I see. That when having it rotating at half crankshaft speed and setup the need of fully opening 30 degrees aTDC and fully clossed aTDC. You need to set the cut out at a large radius. And so large disc / inlet construction needed.

Have thinking of theoretical

Port timing for low blow down. And shorter exhaust and transfer duration

Admiral_dk:
I can't see that changing the shape will improve anything - more likely the opposite - especially if you plan on using Carburetors, as they require a Sharp Rise in Pressure (Vacuum) to propper lift the Gasoline into the Air, for mixture ....

Likewise you need to Shut the Port as quickly for pumping efficiency in the Crankcase ...

A Variable Duration makes much more sense - could be done with two counter rotating Disks. One fixed onto the Crank and the other one about 0.5mm away from it - rotating the opposite direction and likely driven from a belt ....

The Problem will be reduced Reliability + much higher Price ....

Per

BillTodd:
Best get familiar with the equations of motion ;-)

The forces, pressure differential, involved aren't great and the gas mixture aren't massless. To get sufficient mixture past the valve it needs to be open for as long as possible. At higher revs it's probably the moment of the gas column that becomes the significant number .


Interesting gear box. ISTR  Kreidler used a  4 or5 speed plus a 3 speed range changer to get the gear range to fit the ultra low powerband . I remember watching 50s GP racing at Anderstorp in Sweden in 1974  . They were restricted to just 6 gears by then and had to slip the clutch from the start line to the first bend  . They were still accelerating after the first lap .

Vixen:

--- Quote from: BillTodd on November 01, 2025, 09:06:52 AM ---Best get familiar with the equations of motion ;-)

The forces, pressure differential, involved aren't great and the gas mixture aren't massless. To get sufficient mixture past the valve it needs to be open for as long as possible. At higher revs it's probably the moment of the gas column that becomes the significant number .


--- End quote ---

As Bill said 'the moment of the gas column that becomes the significant number'.
So look at this image of a typical disc valve engine. The disc rotates at engine speed to ensure fast opening and closing. Note the wide induction angle of the disc (approx 210* from just open to fully closed). Note also the wide diameter of the induction port, they could not make it any bigger. It's all designed to get the maximum fuel mixture into the engine, in the shortest possible time.
If you need less power, then partially close the throttle.



Hope this helps

Mike

AlexS:
Thanks for explanations!

Per. As idea for variable duration for second disc, powered by a servo?

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