Malossi211-smallframe?

[Truls221]

This is a bit off topic, but as this topic was a little widespread from the start, please forgive me.

First of all I don't think that a big and involving cylinder transplantation is the most reliable you can do to your motor, but when it first is to be done, I would use the PX80 engine case as a starting point. The crankcase is small, with a welded on reed housing you can get a high compression. I think fitting a mal210 would be easy compared to many of the other transplantations done. Capacity 177ccm. Off course weld on and spindle out to the cylinder spigot, fit M8 studs. Not sure about the connecting rod length, but the cylinder can be shortened 10mm from top, set 1mm higher at bottom, increasing the durations of the ports to some very nice numbers. Raising the exhaust port 0,5mm widen it 4mm provide a time-area often only achieved by motocross engines. Exhaust duration 200,1 degrees, main transfer duration 132,4 and blowdown of 33,8. The engine would probably be able to rev to 13000 and with max power at 10000, 30 hp would be no problem. Maybe the gearing would come to short, but then again, a tuned t5 engine reach almost the same revs. Off course this transplantation would be involving in making a purposeful exhaust, and expensive to the cost of decent components like crankshaft, carburetor etc but not much more expensive than normal high level tuning. I think the most favourable issue is that the cylinder kit is cheap and quite easy to replace compared to f,ex an aprilia cylinder and other foreign cylinders. Then fit this engine in a smallframe and you have probably the ultimate thrill!!

[gertax]

I don't think such an engine would ever see more than 10+k rpm. With only 48mm stroke there would be far too little time area, wouldn't it?! Wouldn't fitting a complete P221 engine be much easier with even more fun? It is already pretty hard to get into the 30 bhp range with 60mm stroke, why would it be easier with only 48?

But nice idea anyway... get's one into thinking outside the box

Bearbeitet 20. September 2003 von Gerhard

[Truls221]

With 48mm stroke there is more duration of the ports letting it rev higher. the area of the ports are still the same and the time area is less for the shorter stroke, there is less time for the gasses to flow and they flow faster making more power.

Off course the 221 would make most power of the two at 10000rpm. But with a 221 this would mean a lot of working with the porting layout, changing areas and durations, I don't think the basic design of the cylinder and piston would let this happen. At 12000 with a 221 the piston speed would get too high and the rings will start to flatter when maximum power is achieved at more the app. 9000 rpm. the stroke is the only determinating factor for this to happen.

For me it seems that when combining 48mm stroke with a malossi 210 the proportions become what is more similar to a modern motocross cylinder.

Can somebody else do some calculations around this and see if we get the same results. In the logic theory it's not that far off the line??

[gertax]

With 48mm stroke there is more duration of the ports letting it rev higher. the area of the ports are still the same and the time area is less for the shorter stroke, there is less time for the gasses to flow and they flow faster making more power.

For me it seems that when combining 48mm stroke with a malossi 210 the proportions become what is more similar to a modern motocross cylinder.

Can somebody else do some calculations around this and see if we get the same results. In the logic theory it's not that far off the line??

why should they flow faster? There is less time for them to flow, so they flow less! Simple is that.

Modern MX Cylinders with about the bore of the Malossi (=250cc mx cylinders) have longer stroke than bore. Well, why is that? With the bore becoming bigger displacement increases ^3 whereas cylinder wall only increases ^2. They need the long stroke because they run out of cylinder wall for ports!

Optimum displacement for a two stroke cyl is 125cc with bore=stroke.