Desmodromic valvetrain

[phoenix]

Why hasn't anybody adapted this to a V8? Ducati seems to have had great success with it. With the talk on this board recently about the possible feasibility of pneumatic valvetrains to over come the shortcomings of traditional valve springs, it seems logical to side step valve springs all together. I do know that maintenance on the Ducati can be a bugger and checking valve lash must be done quite often, ( I've heard every 500 miles) but anyone who has a competition engine is used to this! Hey Schmidt, hows this for different?!

[timdog]

Don't ducati still own the patent on this? If so could be why nobody else is doing it

[MadBill]

Don't ducati still own the patent on this? If so could be why nobody else is doing it

I doubt it. Mercedes used it in their race cars in the fifties, so it should be in the public domain.

[BritishTurbo]

It is an interesting system... would be something to experiment with maybe... starting with something simple like a 1 or 2 cylinder engine might be wise though

Are there any disadvantages to the system?

[Mark Workman]

Here's another one.
http://members.chello.nl/~wgj.jansen/te ... atiV8.html

170 bhp/L. Not half bad.

[phoenix]

Some advatages are :

1) Aggressive cam profile - steeper ramps, higher acceleration
than with springs.

2) Better controle of valve - no float.

3) No springs to bind/flutter/break

4) Uses less power - no spring forces to overcome.

[Engineguy]

A Desmodromic valvetrain may have made sense to Mercedes in the mid-1950s when the metallurgy of valve springs wasn't what it is today... and when giant single valves were accomodated by laying them over to 45°... but it's pretty widely accepted that Ducati's persistance in using them was nothing more than stubborn market-driven adherance to a trademark historic idiosyncracy similar to Porsche's long holdout keeping an air-cooled engine flung out there on the wrong side of the rear axle.

At 100mm bore size, for example, using four valves, 16,000-17,000 RPM is currently feasable with steel springs and overhead cams.

So... what are the reasons for not going that route?

[1] Sanctioning body rulebook mandates cam-in-block and/or pushrods and/or two valves per cylinder. OK, what are the chances they'd permit a desmodromic valve closure system?

[2] Self-imposed or economics-imposed restriction to the lower parts count and/or simplicity of cam-in-block and/or pushrods and/or two valves per cylinder. A desmodromic valve closure system doesn't fit that scenario either, does it?

[SchmidtMotorWorks]

I haven't looked at a Ducati in years but I thought their last 4 valve head had cups and springs.

[OldSStroker]

Some advatages are :

1) Aggressive cam profile - steeper ramps, higher acceleration
than with springs.

2) Better controle of valve - no float.

3) No springs to bind/flutter/break

4) Uses less power - no spring forces to overcome.

Not necessarily IMO.

1) The springs aren't really the limit to opening the valve. It's more cam velocity (lift/degree) or inertia loads on the parts.

2) If you mean toss or loft off the nose of the cam, that can be a useful thing. If you define float as bounce on the seat, a positive closing cam can help, but it's causing friction/drag/heat all the time it's holding it closed.

3) Yep

4) Springs give back most of the work used to compress them when the valve closes. The closing cam on a Desmo always needs power to drive it; it never gives anything back.

Desmo is the difficult solution. If you are above the rpm where coil springs work (16K + as mentioned), it's time for pneumatic springs.

My $.02

[cleverlever]

This is a subject with a lot of potential. I patented a semi desmodromic valve actuator in 1988 (4,723,515) I prototyped the mechanism for General motors. The feature I called a "Desmodromic Hook" was part of a variable valve event mechanism

The art work might not be to sophisticated but the concept is clearly illustrated.

Desmodromics have no particular value except at the point of maximum lift where they can reduce the need for a lot of valve spring presure.

They are of particular value on a 2 valve per cylinder engine that has to run at high RPM.

I also made a non variable version of the mechanism that had a little clearance in the hook so the valve event could grow at high speed. I called it controlled valve float.

My web site might be of interest to those who have never seen an engine with reverse flow induction http://cleverlever99.blogspot.com

[larrycavan]

My web site might be of interest to those who have never seen an engine with reverse flow induction http://cleverlever99.blogspot.com

Pretty slick trick! Now there's a manifold on which a hearty appetite could be appeased....looks like at least a 6 burger setup...

Just kidding ya....Nice job!

Don't tell me the stock needles in those Honda CV carbs worked on that thing. Are they 34mm Keihins?

I've got about a dozen questions on that setup but I'll spare you the rest while I did deeper into your website.

Larry C