[Technique] RossiGRM 2strokes boat engine

looks like the pipes vibes the same way the engine does ( rigid on the low end propeller )

that VERY bad for performances

Same as stephane , i would use an YPVS style engine to drive the pipe sliding .....

and still same as stephane = 12.5 13 Cm is HUGE

Do you use shared low end volume for opposite cylinders ?

Stephane a écrit:

is it forbidden to use a programmable ignition (ignitech f.e) where you could use an YPVS servo to drive your exhaust lenght ?
it 'd be more accurate and the pilot won't have to do the job :idea:
13 cm of sliding : that seem to be a lot I.M.O
as it's on an engine for boats, i suppose thaht your working with lower temp of exh gas than on a track bike, so you must also have longer exh system i suppose
wouldn't it be easier to have a classic exh system but an exh valve ?

A servo-control would certainly make it easier for the pilot, but I do not think an YPVS-servo can move four pipes quickly enough against the exhaust gas pressure, estimated at about 0,3 bar in this engine. And if the servo were strong enough, it would require a heavy battery..
130 mm of sliding is about 17% of the normal pipe length; it will give about 2000 rpm extra at the bottom of the power band, and you really need that kind of power because of the propeller characteristics.
I had the same experience with a racing airplane: you need a variable pitch propeller (not allowed under the regulations) or a gearbox (on a plane! Well, at least you will not need reverse...) or a variable exhaust (pipe or powervalve).
A powervalve does not really give you real resonance power; it just prevents the pipe pulses from completely messing up the power curve at low revs. I expect a sliding pipe will make more low-down power. But I would take great care in making sure that there are no leaks at the joints.

SEB4LO a écrit:

Do you use shared low end volume for opposite cylinders ?

That would have been my next question

perhaps, a similar RAVE 2 can working well , no ?

"Do you use shared low end volume for opposite cylinders " : please explain me better, my english is very small....
the engine run with methanol, by the rules we can use only that, the temperature on the exaust with the sensor in the photo position,is about 400/420 C° for the straight run, and about 310 for the turn boa. The electrical sistem for slide the pipes will be the next step, I hope to be able to test the first one before the 2011 racing season that start in May. My friend for the ignition is working on a control box and a wiper glass electric engine from cars....we need a force of about 3 kg for the 125 engine one pipe.[img][Vous devez être inscrit et connecté pour voir cette image][/img]

ROSSIGRM a écrit:

"Do you use shared low end volume for opposite cylinders " : please explain me better, my english is very small....

SEB4LO (ed io) vorremo sapere se i volumi carter di due cilindri contrapposti sono comuni o separati.
Spero che adesso mi capisci, Giuseppe. Se non, allora si può tentare in tedesco o olandese .

fOR all man. no know.. motorsport boat racing
giuseppe rossi onboard camera....

[Vous devez être inscrit et connecté pour voir ce lien]

Grazie Ciccio !

Hello everybody
I'm an Italian guy and this is my first post.

Apropos sliding pipes:
In Uk a lambretta's tuner named Kegra made a pneumatic system for change pipe length in his
speed record lambretta, he called his system KPS:
[Vous devez être inscrit et connecté pour voir ce lien]
I don't have informations about what kind of "logic" he used in this system, probably a pressure valve on the handlebars...

Giuseppe: Is possible to see a power/torque curve of this kind of engine?

Regards.

p.s:Mr Overmars, your italian is fine!

I am new to this site but have been captivated by what is going on here. This is the best echenge of 2 strke information that I have ever seen. It is reall exciting stuff. My father was very involved in 2 cycle engine development in the US and I also am very interested in 2 cycle motors. I currently race hydroplanes with a motor built by Mr. Rossi.

For those of you that do not know Giusseppe, he is a boat racing legend and many time world champion and is truly a wondeful person. What is amazing is that he builds 125,175,250,350,500 and 700cc race motors with almost no help in his shop it Italy. His good work helps keep the sport of hydroplane racing alive.

The sliding pipe used on the motors is very important. First it helps us get the boat on plane. When the prop gains traction in the water the pipe needs to be moved to the longest postiion. Then it can gradually be shortened as the boat gains speed. On the race course we run with wide open throttle all the time and control speed by varying the length of the pipe. We enter the turn full throttle and lengthen the pipe as needed as the increased drag from turning creates load on the engine. In addition we move the motor up and down as we drive. The motor is in the highest position on the straightaways and is in the lower position thru the turn. This is needed because the boats pack enough air under the back that they wil spin out in the turn if there is not enough gearcase skeg in the water.

For those of you that have driven karts with sliding pipes , you know that there is a lot of feel needed to pull the pipe at the proper rate. If you pull too fast the motor slows down as the pipe is too short for the given RPM.

Many years ago we developed an automatic pipe puller for a kart engine. It was pneumatically operated and actuated by a series of RPM switches. It worked great on the dyno but never worked well on the kart...I was always faster pulling the pipe manually. Given the electronics available today I think an electronic pipe pulling system has a much better chance of working well for boat racing.

Having said that, I think that it would be best if we could run with the pipe in the shortest position all the way around the race cousrse. That would allow for a very good seal and minimize laekage and maximize power. For those that spend time on a dyno, you know that a leaky header has a negative effect on performance. The best way to do achieve this could be with a 2-3 speed gearbox that would allow the engine to stay in the RPM range dictated by the fixed pipe length.

We have built a 125cc rotary valve motor with the an Aprilia Cylinder provided by Riley Willey. In addition we are also building a reed valve version at the moment.

And beacuse of the Forum we are building a 24/7 cylinder...that was an eye opener. I will try to post pictures.

This topic is AWESOME!

[Vous devez être inscrit et connecté pour voir cette image]

Welcome, everybody!

[Vous devez être inscrit et connecté pour voir cette image]

Marc..how does one post pictures?

Here are the explainations, but in french...

[Vous devez être inscrit et connecté pour voir ce lien]

Frits Overmars a écrit:

But I would take great care in making sure that there are no leaks at the joints.

I remember a french dealer of moped parts named RGDiffusion made a variable length exhaust and the two parts were sealed as follow:

[Vous devez être inscrit et connecté pour voir cette image]

An other way to fight the leaks is the graphite braided packing but you will need a "presse-étoupe" (I don't know the english word) to compensate the wear of the packing.

[Vous devez être inscrit et connecté pour voir cette image]


PS: thank you all for sharing your knowledge

I have included pictures of our rotary valve motor and the 24/7 cylinder. My good friend Bruce Nicholson does all the machine work.

Sorry to disturb you, guys, but now, i am very curious to learn more about Mr Rossi's work...

[Vous devez être inscrit et connecté pour voir cette image]

Any link?

Marc...go to [Vous devez être inscrit et connecté pour voir ce lien]

Dtenney a écrit:

For those of you that do not know Giusseppe, he is a boat racing legend and many time world champion and is truly a wondeful person.

For those of us who can use a lesson in modesty now and then (and that certainly includes me)..... Respect, Giuseppe!

Dtenney a écrit:

And because of the Forum we are building a 24/7 cylinder...that was an eye opener. I will try to post pictures.

It feels great to see those pictures, Dtenney. But you have got two names mixed up. Your pictures show the FOS-cylinder with symmetric scavenging. The name 24/7 refers to the opening hours (24 hours a day, seven days a week) of an other idea I had: an induction control that acts as a reed valve when the engine has to be started, but swings out of the way when the engine runs in the power band and the exhaust suction takes care of the scavenging.
You'll find a picture + info about the 24/7 here: [Vous devez être inscrit et connecté pour voir ce lien]

gau a écrit:

Apropos sliding pipes:
In Uk a lambretta's tuner named Kegra made a pneumatic system for change pipe length in his speed record lambretta, he called his system KPS.... I don't have informations about what kind of "logic" he used in this system, probably a pressure valve on the handlebars...

[Vous devez être inscrit et connecté pour voir cette image]
With this pneumatic activation I suppose the pipe is either long or short, without the possibility of intermediate lengths.
Giuseppes intended approach with a windshield wiper-motor probably offers better control.
It also makes a difference whether you slide the initial small-diameter part of the pipe, or the belly.
Lengthening the small-diameter part not only lengthens the path for the resonance waves, but also lowers the Helmholtz frequency more effectively than lengthening the belly.
And I like the simple sealing in Maneton's pictures. I like simplicity anyway; that is why I like two-strokes .

Frits...thanks for the correction. My mind hit the rev limiter!