Help! Rotary valve shape

[TZ350]

Help. My bucket needs more "Go" for Taupo. Who knows the proper shape for a Suzuki GP125 rotary valve inlet? I know that changing the inlet port at the valve face from a round shape to a wedge shape has some benifits like increased area and quicker opening/closing. But what I want to know is, should the area of the modified port be the same as the carburetor or should the inlet taper in some way so the port has more area, the same size or smaller for gas velocity like in a four stroke? Has anyone seen inside a rotary valve gocart or road race engine? Has anyone information on Suzuki factory RG500 racers or early rotary valve road race engines or an Aprilia perhaps? Any information or positive comments would be a great help.

[Slingshot]

And once you find out, can you let me know please.

It would be great if you could take some photos of you rotary valve before and after modification too.

From what I understand, a GP125 disk will fit into a GP100 so I'm on the hunt for a spare Gp125.

[Skunk]

Warning: I know Jack Schmidt!

My guess would be to clean up the port and match everything up. A slight taper would possibly help.

Does A. Graham Bell have anything to say on the matter?

[Slingshot]

I've just found this PDF (http://www.bridgestonemotorcycle.com/documents/BSTuning6_low.pdf).

It's cool on so many levels.

It's not specific to the GP125 but it does have diagrams of rotary valves.

[pete376403]

If you can get a supply of rotary discs then it's easy to modify the inlet timing until you find the best combination of opening and closing.

At the Suzuki discs fibre or stainless? My Kawasaki F9 (1972, 350 single) had a stainless disc. I trimmed the opening side just a tiny amount and it did seem to make quite a (seat of the pants dyno) difference.

I never bothered much with opening up the inlet port, just matched the hole in the case with the hole in disc cover.

Some pics here of an inlet port of an RG500 which might give you some idea
http://rg500-gamma.hp.infoseek.co.jp/gamma/engine/engine.html

[saxet]

A GP125 disc will fit straight into a GP100 but it's benifits without porting mods ...I couldn't say. I do know that on a reasonably ported GP125, the standard disc can be opened up 5 deg earlier.

[saxet]

The info I've seen sugests no mods to the port from the disc valve into the crankcase. the idea that the shape could be changed to increase opening area the trade off may be carb fuelling probs as rotary disc valves are supposed to suffer from fuel stand off probs when heavily modded. Info I've seen seems to focus on actual port mods in conjuction with other mods. If you play around and learn something let me know!

[Buckets4Me]

just a pic to show the difference betwen a standard gp100 and gp125
rotary valve

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