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.

[husaberg]

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.

Cool KR3 photos i had never seen those pics.
the 1989 Cagiva had the atac and rotary PV but there were a lot of cross pollination with Cagiva and Yam.
the Last Cagiva tested extending headers with Chandler in practice with a hydraulic pump by tag and extended 20mm. (100 bar)

[Flettner]

So collectively we are saying a reverse cone that shortens the pipe and steepens that same cone at the same time, with no extra complication than say a ATAC system, is worthless?

[Peter1962]

Would it be possible to add an ATAC chamber, to an existing modern 250cc two stroke MX or enduro engine that is equiped with an electronic powervalve ? (thinking of the 250 and 300 cc KTM models from 2023 and up) If so, the added torque in the lower RPM's could make it a formidable weapon against the fourstroke armada.

[Frits Overmars]

So collectively we are saying a reverse cone that shortens the pipe and steepens that same cone at the same time, with no extra complication than say a ATAC system, is worthless?

No.
Ever wondered why ATAC-pioneer Honda abandoned ATAC as soon as they developed a way to circumvent Yamaha's rotating powervalve patent (which in turn lead Yamaha to copy Honda's sliding powervalve)?
Shortening a pipe may be more cumbersome but it is also much more effective. But it should be done with a sliding header instead of a sliding reverse cone, as I tried to explain here earlier.
Having said this, I enjoy your out-of-the-box thinking and I would like to know how you plan to steepen a cone.
Mind you, reverse cones can be too steep. Then they will generate shock waves instead of decent stuffing pulses.

[lohring]

Our experiments with the sliding baffle (reverse) cone showed that moving the diffuser section didn't matter much if you hold the tuned length (reverse cone position moved to maintain the same tuned length) constant. Moving the reverse cone definitely effected the power; mainly by changing the tuned length. It also made the power band width worse. The designed position of the cones gave the best result. In all other experiments on experimental tuned pipes, we change the tuned length by moving the whole pipe along the header.

Lohring Miller

[Peter1962]

No.
Ever wondered why ATAC-pioneer Honda abandoned ATAC as soon as they developed a way to circumvent Yamaha's rotating powervalve patent (which in turn lead Yamaha to copy Honda's sliding powervalve)?
Shortening a pipe may be more cumbersome but it is also much more effective. But it should be done with a sliding header instead of a sliding reverse cone, as I tried to explain here earlier.
Having said this, I enjoy your out-of-the-box thinking and I would like to know how you plan to steepen a cone.
Mind you, reverse cones can be too steep. Then they will generate shock waves instead of decent stuffing pulses.

Frits, do you know why Thijs Hessels who had a working prototype of a sliding header system, did not go further with this development ? Were there technical difficulties, like for example sealing issues ?

[Flettner]

No.
Ever wondered why ATAC-pioneer Honda abandoned ATAC as soon as they developed a way to circumvent Yamaha's rotating powervalve patent (which in turn lead Yamaha to copy Honda's sliding powervalve)?
Shortening a pipe may be more cumbersome but it is also much more effective. But it should be done with a sliding header instead of a sliding reverse cone, as I tried to explain here earlier.
Having said this, I enjoy your out-of-the-box thinking and I would like to know how you plan to steepen a cone.
Mind you, reverse cones can be too steep. Then they will generate shock waves instead of decent stuffing pulses.

How steep is too steep?