nelson71

I just recently became aware of the Ducatti Desmodromic valvetrain system. The whole idea of eliminating the valve springs seems like it would be beneficial in any high rev/ high lift application. Plus you would not have the loss of HP that it takes to compress the valve srings. So why hasn't this system become mainstream in a variety of applications?

Vertigo

iTrader: (1)

If i remember correctly there is a working engine that was designed by Virginia Tech. Not 100% sure though

Esoteric[TG]

Why is the rotary engine a rarity? It is a great system at least in theory, but it is not very well understood/developed.

I think one of the main reasons for it not becoming more mainstream is the complexity of the system and need for frequent adjustment to keep it working correctly. As far as being beneficial in high rpm, high lift situations, yes it can be, and you are also correct in that it causes fewer parasitic losses compared to a more conventional valvetrain.

I believe that Ducati still uses the system on at least a few of their engines. I would be lying if I tried to say which ones, but I'm pretty sure they still do.

Hopefully someone will continue developmment of this type of valve control. It certainly holds a lot of promise.

waSStock

Give the Duck some time(miles)...it'll answer the question for you.

Anonymous

The system works but it is expensive to manufacture and hard to keep in adjustment. It is also difficult to get the adjustment right in the first place.
Most Ducati dealers can't even get it right.
They have problems all the time. I have a few friends that own them.

That is why people compare them to Ferrari. Pretty to look at, but unreliable, break frequently and slower than other bikes 1/2 their price. Exclusivity has its price.

Old SStroker

Mercedes use "desmo" valves on the 1954 W196 Grand Prix car. This was carried over into the '55 SLR racing sports car. I think they used one cam to open the valves and one to shut them. I'll bet setup was fun. I can see it now: one mechanic for the opening cam and one for the closing cam. You don't have to use 2 cams, but the mechanical bits are complex even with one cam. Don't you still have to have a least a tiny bit of lash at valve closed position? I can see burned exhaust valves a good possibility with desmo.

Pneumatic springs are a lot simpler than desmo. IMO, desmo had it's 15 minutes of fame in the '50s when decent valve springs were a real problem. At least the Germans (Mercedes) made desmo work fairly well.

FWIW, opening the valves against a spring isn't a total waste of energy. The spring gives most of that back when it closes the valve. Some does go into heat of course.

bshell

iTrader: (24)

There's also some interesting R&D work going on with electronic and electro-hydraulic valvetrains. Here's an article about an engine designed by Lotus:
http://www.all4engineers.com/index.p...alloc=33/id=45
The ability to alter valve lift and duration w/o opening up the engine is what caught my interest...

Anonymous

On the Ducati Superbikes (916, 996, 998, 999) it is DOHC but...

There is one cam for the exhaust and one for the intake.
Desmo set ups actually have a cam follower on the top and on the bottom of the same lobe for the opening and closing actuation.

However, I believe there were earlier designs with seperate lobes (if I remember correctly) one to open the valve and one to close the valve.
(the lobes were side by side very close with forked followers)

Skele4door

iTrader: (1)

Another benefit of infinitely adjustable valve timing is that you can get rid of the throttle body. You don't need a turbulence inducing plate when you can control the amount of airflow going into the engine directly at the valves.

digitalsolo

iTrader: (24)

Another interesting alternate valve configuration....

http://www.coatesengine.com/

Very impressive, I understand the sealing of the cylinders still needs some work though.

J-Rod

Desmo has its own set of issues. The biggest one I remeber reading about was the system did not respond well to valve float (read that as being over revved) at all.

Old SStroker

One of the primary reasons for the Desmo system is to prevent valve float or loft by attaching the valve to the actuating mechanism.

http://en.wikipedia.org/wiki/Desmodromic_valve

Awake455

Ducati still uses the desmo setup widely. Costly, requires quite frequent maintenance, as said earlier some dealers aren't all that good at adjusting them.

IIRC, there is not a problem (as long as the adjustment is close) with burning valves. What owners of an engine with too much valve lash will notice first is a reduction in lower rpm power due to some bleedoff during the compression stroke. As the rpms rise, the increased cylinder pressures will tend to make the valves seal more completely.

Also, the radically aggressive profiles that are possible when ya don't have to worry about overpowering a spring or bouncing a valve off of the cam lobe tend to be very stressful on valvetrain components. The more power the factory tries to eek out of a particular engine package, the more frequent the cam follower adjustments.

Old SStroker

There just ain't no free lunches are there?

J-Rod

I didn't have the material in front of me that talked about the desmo stuff. I could obviously be wrong on the valve float. I just remember that they had issues if you tried to rev them too much. I'll see if I can find the issues, but it sound like folks are covering them pretty well.

black_z

iTrader: (4)

One thing about the rotary is that they arent very efficient, and they arent very environmentally friendly. The typical 4 stroke automotive engine is ~25-30% efficient. The rotaries are ~19-23% efficient. Although, I believe if they were further developed and there was more R&D put into rotary motors, that they could greatly improve upon them.

ronbros

I have a mazda rotary i makes 420whp in a RX-7 2600 lbs. its a big block rotary 80 cu.in., NOW if GM had continued in 73 to develope there 200cu.in. rotary i wonder what HP it might have been, damn them bean counters. RON in DAYTONA

TRex

iTrader: (3)

Rotaries are very efficient when you measure them in terms of hp/weight ratio. However it is true that they are not very efficient with respect to hp/lb of fuel burned.

ronbros

VERY true, rotarys like a lot of fuel, but for racing WOW! ,I witnessed an 80cu.in. 2 rotor engine make 800flywheel HP on methanol, HEY I was impressed, it had 8 fuel injectors, but like I said GM and 200cu.in.rotary, a streetable Corvette with 1500hp, YES let me toss that in,, the engine I watched idled at 1000rpm smoothly, no vibration! we then wieghed it 214 lbs with assoreys, my car gets 18-20 mpg, on 93 octane, at cruise 70mph, ------- 82 Z28 467" BBC 8-12mpg my other car, around 450whp 3570lbs. Guess which one is faster, stops better, and goes around corners quicker, but the Camaro does have faster top speed 175-180. anyway just some thoughts RON in Daytona

Old SStroker

It's deja vu all over again. Here's a rotary discussion. Lot's of 'what ifs" there too.

http://web.camaross.com/forums/showthread.php?t=404763