Why no Desmodromic valves in cars?

[HardDrive]

Hmmmm....not specifc I suppose to 911s, but it did come up in a discussion about replacement pistons (valve pockets actually).

For those not familiar, a Desmodromic valve train (as the folks at Ducati would call it) in effect has 'lifters' that pull in both directions. In other words, the valve is pulled open, but instead of a spring pulling it shut (as we typically find on cars), it is also pulled shut.

Are these systems used in F1 cars?

Other than increased complexity (and cost), are there disadvantages?

[beepbeep]

There is no need. Cars don't rev that much and even if they did there are other ways.

F1 cars use pneumatic valve lifters with finger-followers. With other words, no desmo valves but fairly conventional system where spring is replaced by gas-pressure.

[GreenWater]

Springs work just as good as desmo. does. A CBR400 revs to about 19000 rpm and it has a normal spring operated valve system. Desmo is just unneeded internal moving parts. It is a good solution to floating the valves at high rpm. Totally fixes that problem. Many motorcycles rev very high. The new yamaha r6 revs to 16,200 rpm. It also has a spring valve system. I think there is many reasons why cars don't have desmo valves, but floating the valves in a car is not a problem. Car engines don't rev very high because the engine tolerances are not as high as a motorcycle or F1 car. In turn, look at how long a typical engine lasts in a motorcycle or F1 car. Motorcycle engines are done at about 60,000 miles, and F1 car? Maybe one race. So, spring operated valves are not the reason why car engines don't rev very high, it's other issues.

[atlporsche]

http://members.chello.nl/~wgj.jansen/

check this guy out...a "museum" of desmodromology...shocking how much of it was out there.

sjd

[jluetjen]

Originally posted by GreenWater
Springs work just as good as desmo. does.

I agree. The big benefit is that springs are lighter and cheaper, both of which are big benefits. Desmo systems in cars were somewhat in vogue back in the 50's when engine speeds started to increase, but the metalurgy of the springs hadn't advanced fast enough to support the desired engine speeds.

A CBR400 revs to about 19000 rpm and it has a normal spring operated valve system. Desmo is just unneeded internal moving parts. It is a good solution to floating the valves at high rpm. Totally fixes that problem. Many motorcycles rev very high. The new yamaha r6 revs to 16,200 rpm. It also has a spring valve system.

Good points, but I'm not sure if those are the best examples within the context of cars. The big difference between car engines and motorcycle engines is that the valves in car engines are bigger, and thus weigh more and have more inertia then the valves in bike engines. Never the less, springs still work all the way up to CART race engines when it comes to rev's, and so springs don't have much trouble keeping street car valves under control.

I think there is many reasons why cars don't have desmo valves, but floating the valves in a car is not a problem. Car engines don't rev very high because the engine tolerances are not as high as a motorcycle or F1 car.

Here we disagree. Automobile rev limits have relatively little to do with the build tolerances. If car manufacturers wanted to build engines with the HP per liter of a sport bike engine, they are capable. Look for example at the Honda S2000. But that car also shows why car manufactorers don't bother. Given a car's weight of 1-1.5 tons, an engine's ability to pull the car from rest up to 30 MPH quickly is important since most cars spend a lot of their life in that range. A motorcyle type engine would either need to shift 3 times to do that quickly, or never get on cam. The S2000 is a nice car, but it's sales pale compared to similar sized cars with 3 liter motors. So the car manufacturers optimise their engines for the desired 1000-6000 RPM rev range. This optimisation also includes the costs.

In turn, look at how long a typical engine lasts in a motorcycle or F1 car. Motorcycle engines are done at about 60,000 miles, and F1 car? Maybe one race.

Actually the current rules stipulate that F1 engines need to last 2 race weekends which is pretty incredable considering that they also spend most of their time between 15,000 and 20,000 RPM.

So, spring operated valves are not the reason why car engines don't rev very high, it's other issues.

Yeah. I agree.

[wholberg]

[i]

Other than increased complexity (and cost), are there disadvantages? [/B]

I think that hit the nail on the head. For most of the 20th century, the development of american cars has been ruled by corporate profitably, not technology. American auto manufacturers defended their decision not to build integrated roll cages into automobiles (using race car technology) because it would have increased the cost of automobiles about $300 per car and they did not think they could recoup that from consumers. The argument that integrated roll cages would save tens of thousands of lives per year was overruled by profitability.

Secondly, desmodronic valve systems require more maintenance. The average American wants a car that never needs maintenance. When I tell people that I adjust the valves on my car every 12-15K miles, the typical response is why didn't Porsche just use hydraulic lifters like everyone else (don't go there).

[dougn1]

i think the biggest advantage of a desmo system is the the valve acceleration can be steeper. in other words the cam can have steeper sides when there's no spring force resisting the valve movement.

[KobaltBlau]

Originally posted by wholberg
When I tell people that I adjust the valves on my car every 12-15K miles, the typical response is why didn't Porsche just use hydraulic lifters like everyone else (don't go there).

I think more people in your life know about hydraulic lifters than in mine.

[drl911]

The desmo valve system is kinda of what makes a Ducati a Ducati. They are somewhat corporately "stuck" with it now tooling and marketing wise for most of their models. Similiar to 911's always being air cooled.... oh wait a minute

Dan

[Hendog]

Desmodronic valves? I just learned something today; that's why I love this board

[HardDrive]

Originally posted by Hendog
Desmodronic valves? I just learned something today; that's why I love this board

Arguing about obscure mechanical technology.....one of the many benefits to hanging out with Porsche owners.

[sand_man]

I can't remember for certain (I have it in a book some place), but didn't the "orginal" Mercedes 300SLR of the 1950s utilize the desmo. valve technology? Maybe it was the 196..I'll have to check when I get home.

[jluetjen]

Yup. It was the 300SLR (but not the street version 300SL).

[RarlyL8]

I thought the big deal for desmo valve trains were the elemination of float. That is always a concern with the spring system.

[buster73]

Originally posted by sand_man
I can't remember for certain (I have it in a book some place), but didn't the "orginal" Mercedes 300SLR of the 1950s utilize the desmo. valve technology? Maybe it was the 196..I'll have to check when I get home.

Mercedes W196 and 300 SLR race cars used desmodromics. For the mechanics a nightmare to set-up and keep adjusted.

[Shuie]

Originally posted by buster73
For the mechanics a nightmare to set-up and keep adjusted.

Precisely. People always whine about the 'maintenance' costs of owning Ducs. The 'maintenance' being the valve adjustments that require a trained technician. The process/tools/training required to adjust a desmo valve system would make our cars a little less user friendly. Desmo valves are for Ducatis.

[Jeff Jagusch]

Also, consider how much friction is involved in rotating the cam with valve springs?

Someone should be able to come up with this figure.

I want a Ducati especially the new sport 1000 retro bike!

Jeff

[Noah930]

Desmo systems in cars were somewhat in vogue back in the 50's when engine speeds started to increase, but the metalurgy of the springs hadn't advanced fast enough to support the desired engine speeds.

I can't recall exactly where I've read it, but I think poor metallurgy back in the 50's was the reason for developing desmodromic valvetrains. Valve springs couldn't withstand the forces involved. I think that's also why Ferrari experimented and used hairpin-type valve springs (instead of traditional coil springs) in the 1930's and 40's.

When Ducati (Taglioni) started using desmo valvetrains in 1956, he wrote: "This system, which we call desmodromic, has demonstrated its greater efficiency for many years now, even if it is mechanically more complicated and more costly."

[Nine9six]

Originally posted by dougn1
i think the biggest advantage of a desmo system is the the valve acceleration can be steeper. in other words the cam can have steeper sides when there's no spring force resisting the valve movement.

This is a true statement, but there are drawbacks as well. That steeper cam lobe gets pretty vicious on the rockers. The steeper you go, the more you beat the pi$$ outta the rockers.
Corse cam grinds on the Ducati superbikes take their toll.

[Nine9six]

Originally posted by Shuie
Precisely. People always whine about the 'maintenance' costs of owning Ducs. The 'maintenance' being the valve adjustments that require a trained technician. The process/tools/training required to adjust a desmo valve system would make our cars a little less user friendly. Desmo valves are for Ducatis.

Thats cause most of those whiners are posers. I own a ducati, and I adjust my own valves. Like anything else, it takes time and patients. Oh, and a little investment in opening and closing shims for proper adjustments.