reed vs rotary

[FurlanPx]

a simple question....why with a reed valve can I reach high performances than a rotary valve on a vespa px (177polini) engine?

I think this topic was just discussed....if it was anyone can give me a link?

bye

Marco from Udine, Italy

[amazombi]

a simple question....why with a reed valve can I reach high performances than a rotary valve on a vespa px (177polini) engine?

I think this topic was just discussed....if it was anyone can give me a link?

bye

Marco from Udine, Italy

<{POST_SNAPBACK}>

that's mainly because on px engines it's not really possible to get decent inlet port timing with a rotary valve. the inlet is on the wrong side of the cylinder. if you modify the crankshaft you will only manage to close the inlet later, which, from a certain point, ceases to be helpfull. it's not possible (at least i can't think of a way) to open the inlet earlier, which would be much more desirable. with a smallframe engine this is much less of a problem. the second drawback with the vespa reedvalve in general appears to be the somewhat limited inlet port area, a problem at least partly dealt with when converting to a reed valve inlet.

[FurlanPx]

that's mainly because on px engines it's not really possible to get decent inlet port timing with a rotary valve. the inlet is on the wrong side of the cylinder. if you modify the crankshaft you will only manage to close the inlet later, which, from a certain point, ceases to be helpfull. it's not possible (at least i can't think of a way) to open the inlet earlier, which would be much more desirable. with a smallframe engine this is much less of a problem. the second drawback with the vespa reedvalve in general appears to be the somewhat limited inlet port area, a problem at least partly dealt with when converting to a reed valve inlet.

<{POST_SNAPBACK}>

ok, I see.... but there's a way to let the valve open early, you have to remove material of the valve on the "cdi side" not the "cilynder side", and so the valve opens earlier. In my last engine I used a timing like 170°+70°, and an area of the valve same like the area of 28phbh venturi.... I think the only problem is that when the crank start to close the valve, the inlet area start to reduce and doesn't perform like when is totally opened(that has the same area of 28venturi)....and when you use a reed valve there's not this problem, the inelt area is the same during all the inlet timing.

bye

Marco from Udine, Italy

[manni]

In my last engine I used a timing like 170°+70°

That´s not possible. Imho the earliest point is 130°.

[FurlanPx]

yes sorry 130-70 not 170-70, too many 70 :P

[amazombi]

the timing itself is very much what you'd want it to be, the only problem is see is what you mention yourself: with the inlet port strechted so long it is not fully open for a very long time but obstructed by the crank's flat outer side to a smaller or greater extent for most of the time. but i have to admitt that i'm smallframe only (largeframe years and years ago), so I'm only talking from faint memory and from transfer from a different engine.

[FurlanPx]

schade

so now start with reed valve...