Sportbike World banner

1 - 20 of 26 Posts

·
Registered
Joined
·
373 Posts
Discussion Starter #1
In the 1960s Ducati introduced the Desmo valve, and almost every other company had common valve springs. This company introduced another way to close the valve. It was state of the art and allowed the engine to rev to 10,000 RPM when all other engines of that time only reved to 6,000 RPM.

What year, make, and model was it. What type of valve return mechanism did they use?

Andy
 

·
Registered
Joined
·
373 Posts
Discussion Starter #3
Hi Mike,

Sorry it was not Pneumatic valves. This was a production motorcycle that was very popular.

Andy
 

·
Registered
Joined
·
373 Posts
Discussion Starter #5
Sorry Smeghead... It has nothing to do with the camshaft.

It was a device used to close the valves. It was not desmo, coil springs, or pneumatic.

Andy
 

·
Registered
Joined
·
373 Posts
Discussion Starter #11
The helical spring when compressed causes each coil to rotate/twist similar to a torsion spring.
 

·
Premium Member
Joined
·
397 Posts
That's more or less correct.:)
A helical spring is a torsion bar, formed into a cylindrical spiral. Generally a much more efficient use of space and the engineer can get away with using less exotic materials. In the sixties torsion bars were a real "selling feature".:D
 

·
Retired Moderator
Joined
·
943 Posts
It's not fair :(

You play the nice trivia on the weekend when I can't play :crying:
Nice question Grok! Excellent trivia Andy!

I would like to add one more question :)

Fabio Taglioni is considered the father of the desmodromic system, but the desmo was first used in a racing car long before.
Taglioni perfected it and also made it possible to manufacture and produce it.
Which was the racing car? It was very fast, exclusive and also very famous.
Also what is the big advantage of the desmodromic system apart from being able to seal the valves at very high revs where a spring would have to be so hard that the friction would actually be a problem?

Aris
 

·
Registered
Joined
·
373 Posts
Discussion Starter #14 (Edited)
Hi Aris,

Here is what I think you are refering to:

"1954 Mercedes (Germany) - Employs desmodromics on it's W196 GP car; 2.5L, 260hp straight eight engine. During development all springs are removed from system. Complexity goes down, performance unchanged. W196 proceeds to win two world championships. Also used on Mercedes' 300 SLR Sport race car."


Picture source: http://www.angelfire.com/mi/allishan/maxmodels.html

Regarding the advantage of a desmo system:

"Aggressive cam profile - steeper ramps, higher accelerations than with springs"

Link source: http://www.teamyikes.com/desmo.html

Now here is a question...

What is the disadvantage (Horsepower wise) of the desmo system?

Andy
 

·
Premium Member
Joined
·
397 Posts
I did my share of 450 top ends

The cheap hop-up of the day was to swap the left and right torsion bars, this allowed a bit more preload (they featured indexed splines) which resulted in a higher redline. :D
 

·
Retired Moderator
Joined
·
943 Posts
Andy said:
Now here is a question...

What is the disadvantage (Horsepower wise) of the desmo system?

Andy
Hi Andy,

You re right about the Mercedes W196 and 300SLR, that's what I had in mind :)

You caught me by surprise with your question though. Do you mean that at the same revs, a conventional engine will produce more power than a desmodromic enine? :confused:

Hey desmo079 where are you?? We need some help here! :D

Aris
 

·
Registered
Joined
·
373 Posts
Discussion Starter #18
Hi Aris,

What I mean is, why does a desmo valve design not allow 14,000 RPMs like today’s superbikes engines that use conventional coil springs.

Andy
 

·
Registered
Joined
·
1,188 Posts
ariszr7 said:
Hey desmo079 where are you?? We need some help here! :DAris
I think he is plain wrong.

Because there are no valve springs pushing on the cam during 360 degrees of rotation there is very little friction. A comment was made about the 300SL was that one could turn the cam with just two fingers.

Theoretically desmo valvetrains can turn an INFINITE number of RPMs. The only limiting factor would be that the mechanism itself may break. I am not sure even that would prevent a modern desmo motor from turning over 14k.

In fact if Andy is talking about twin cyl motors, it may be the carnk, pistons, or rods that would fail above 14k. That may be solved with the new Ducati V4.


Andy, where did you get info that a Ducati twin can't turn 14k?

Are you saying that the RC51 and the Mille sp can turn higher rpms? Maybe they have to turn higher revs because the Ducatis can breathe their valves a lot deeper, and Ducatis just don't need any more revs???

I'd be interested in your source of info.
 

·
Registered
Joined
·
373 Posts
Discussion Starter #20 (Edited)
Hi Desmo,

I have no idea as to weather a desmo valve design can or cannot spin up to 14,000 RPM.

I should have said... Does the desmo valve system limit the maximum RPM. Would it spin faster (say 1,000 more RPM) if it went with coil springs?

I only read some comments made by others at epinion. Here is the link: http://www.epinions.com/auto-review-1C2-23199D40-39F3E917-prod3

And here are some of the follow up comments made by others:

http://www.epinions.com/auto-review-1C2-23199D40-39F3E917-prod3/show_~allcom

Quote from above:

"I agree that Desmo systems do not have this liability, but the greater reciprocating mass of the Desmo components does limit engine speed compared to a valve spring setup"

Andy
 
1 - 20 of 26 Posts
Top