ESE's works engine tuner

[lohring]

Sliding pipes are common on racing outboards. See https://www.facebook.com/watch/?v=389274510418137 They are a sliding fit without seals. A friend made a sliding pipe with seals that was coupled to the boat's rudder. It lengthened in the turns as the rpm got pulled down. I built a pipe with a manually adjustable baffle cone. It depended on fit for a seal. Pipes are creating shock waves that don't depend on a good seal. Our pipes develop around 100 inches of water or 3 to 4 psi at the large diameter. We water cool the pipe to header connection to save the o rings. Again, we have lots of cold water.

Lohring Miller

[wobbly]

As the 2:1 Y pipe scenario works best with what would be considered " radical " 200* Exhaust duration ( with all the downsides of that ), the thought occurred to me that if you are happy
to go to all the trouble of adding a " third leg " ATAC, then why not arrange a flap valve inside the Y that alternately shuts of the leg to the opposing cylinders in turn.
Sure it has to operate at the crank rpm ( that is relatively low in this case ), but with some lateral thought it may be possible.
EDIT - after a coffee I thought of a pair of inline drum valves driven with a tooth belt off the crank.

The other " cheat " available is to cut the piston skirts slightly short, such that the port, and thus the crankcase, is open to the Y when each piston is at TDC.
This plays absolute havoc with the fueling, but pumpers can be made to work with it, and it increases power everywhere.
Been there, done that, won the " Stock " Jetski Title.

[katinas]

Thank you Frits for the photos, the result is clearly visible in the graph.

[Storbeck]

As the 2:1 Y pipe scenario works best with what would be considered " radical " 200* Exhaust duration ( with all the downsides of that ), the thought occurred to me that if you are happy
to go to all the trouble of adding a " third leg " ATAC, then why not arrange a flap valve inside the Y that alternately shuts of the leg to the opposing cylinders in turn.
Sure it has to operate at the crank rpm ( that is relatively low in this case ), but with some lateral thought it may be possible.
EDIT - after a coffee I thought of a pair of inline drum valves driven with a tooth belt off the crank.

The other " cheat " available is to cut the piston skirts slightly short, such that the port, and thus the crankcase, is open to the Y when each piston is at TDC.
This plays absolute havoc with the fueling, but pumpers can be made to work with it, and it increases power everywhere.
Been there, done that, won the " Stock " Jetski Title.

Does the short skirt trick work without the super high duration? Currently at 195 and having trouble getting an impeller flat enough to work well so a little hesitant to go further.

Looks like I'm better off to put the effort into figuring out the pump then bump up to 200 degrees of I want to get frisky.

The rotary valve thing is cool but a bit more than I'm willing to take on at this point

[Flettner]

As the 2:1 Y pipe scenario works best with what would be considered " radical " 200* Exhaust duration ( with all the downsides of that ), the thought occurred to me that if you are happy
to go to all the trouble of adding a " third leg " ATAC, then why not arrange a flap valve inside the Y that alternately shuts of the leg to the opposing cylinders in turn.
Sure it has to operate at the crank rpm ( that is relatively low in this case ), but with some lateral thought it may be possible.
EDIT - after a coffee I thought of a pair of inline drum valves driven with a tooth belt off the crank.

The other " cheat " available is to cut the piston skirts slightly short, such that the port, and thus the crankcase, is open to the Y when each piston is at TDC.
This plays absolute havoc with the fueling, but pumpers can be made to work with it, and it increases power everywhere.
Been there, done that, won the " Stock " Jetski Title.

What was the BSL reverse cone angle?

[wobbly]

The BSL500 pipes, the later Titanium sets were similar rear cones to the RSA125 Tubo 102.
The pipes were longer and fatter but the rear angles were much the same.
EDIT - those angles only work for very fat pipes used in a road race situation.

[katinas]

[QUOTE= cagiva on the v93 ran a pV and atac system together in parallel (well series)[/QUOTE]

Suzuki, Yamaha, Roberts KR3 also used dual exhaust control.
From 1995 on rgv250 and 500 screw on chamber type with separate control of pv and atac.
Yamaha may have used from 1999 an integrated chamber into the cylinder that opens and closes like one unit with drum type powervalve. Since 2001 only Biaggi spec cylinders, with double exhaust ports, had a removable type atac chamber . 2002 all latest YZR 500 equipped with engines similar to Biaggi's 2001 type.
Latest TZ 250 5KE4 cylinders made with cast in camber type like on Olivier Jacque's YZR 250 2000 .
Roberts KR3 cylinders also with a removable chamber but operates like one unit with pv.