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Porsche with desmodromic valves

An interesting site on desmodromic valve systems. (A cam opens AND closes the valve instead of a spring)...Ducati's claim to fame but also used in an experimental air cooled porsche type 753

http://members.chello.nl/~wgj.jansen/text/porsche.html

the patent

http://members.chello.nl/~wgj.jansen/patented/porsche.html

and main page

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

Anyone know anything else about this engine?
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Last edited by m110; 03-11-2009 at 01:59 PM..
Old 02-20-2009, 08:13 PM
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The 753 was the 1.5 liter flat-8 from the 804 F1 car. I never heard of that engine having desmodromic valves. Ludvigson's book called them "finger followers" but never mentioned "desmodromic". I also thought springs were involved. The only cars I know with desmodromic valves are the 1955 Mercedes Silver Arrows 300SLRs like what Fangio drove in F1. Straight-8 cylinder, MFI, great cars.

I always though Ducatis were interesting for those desmodromic valves. They have advantages and disadvantages, though. They are free-revving from low rpm but the power required to drive the valvetrain increases with speed, unlike the fixed-spring pressure systems. This means that the desmo eventually will have more power used to drive the valves at the same speed as a spring setup.

However, the desmodromic setup has much less valve float, provided you can keep the valve in complete sealing contact with the seat through careful maintainance of the closing cam tolerances and adjustment.

I do not know of any Porsche engines built with desmodromic valves, though I would be interested to see photos showimg otherwise. I would not be surprised to see drawings from engineering proposals from the Porsche engineering consultancy. The 916 and 547 four-cammers were complex enough to work with air-cooling. I do not think desmo would fit the air-cooled architechture without significantly re-engineering the design of the basic Porsche engine principles.
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Old 02-20-2009, 08:54 PM
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Seems like you could combine this with roller cams to make for less friction and power loss.
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Old 02-20-2009, 09:31 PM
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from babelfish:
"the invention refers to a valve gear for high-speed internal-combustion engines with which the opening movement of the valve by one with a cam co-operating rocker finger is reached and close movement effected via double-armed levers, which attack at the valve and co-operate with cam discs"

It kind of sounds like it is describing a desmo valve train. The finger sounds like a normal rocker arm and the double armed lever sounds like the closer arm on a Ducati. Without valve springs there is very little internal friction loss in the valve train. A Ducati engine can be turned over very easy by hand with the plugs out because there are no valve springs to compress. The positive valve closure allows the racing Ducatis to spin much faster without the need for pneumatics. The biggest Ducati disadvantage is the difficulty in setting the very exact valve clearances.
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Old 02-20-2009, 10:22 PM
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Quote:
Originally Posted by Flieger View Post
I do not know of any Porsche engines built with desmodromic valves, though I would be interested to see photos showimg otherwise. I would not be surprised to see drawings from engineering proposals from the Porsche engineering consultancy. The 916 and 547 four-cammers were complex enough to work with air-cooling. I do not think desmo would fit the air-cooled architechture without significantly re-engineering the design of the basic Porsche engine principles.
A diagram of the experimental 753 valvetrain. The producyion 753 was described by Randy Leffingwell as taking 220 hours to assemble (nearly double that of a 4 cam)

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Old 02-20-2009, 10:30 PM
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That is a pic of a desmo valve train - eerily similar to the modern Ducati setup, even down to the drilled/lightened closing cam lobes.
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Old 02-20-2009, 10:34 PM
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Paul Frere uses 2-3 pages in "The Racing Porsches" for the 753 (1.5 liter) and 771 (2 liter) flat eight engines. He mensions nothing of desmodromic valve train.

There is a drawing of the 771 engine:


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Old 02-21-2009, 02:37 AM
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The 753 and 771 was desiged together with the same stroke (54.5 mm) but different bore, 66 vs 76 mm. 753 was designed for formula 1 Grand prix racing and the 771 was used in the 718 spyder and later in the 904.
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Old 02-21-2009, 02:57 AM
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Quote:
Originally Posted by Bill in OKC View Post
The biggest Ducati disadvantage is the difficulty in setting the very exact valve clearances.
Yeah, i've had to sand my shims to get things exact at times, but kinda in keeping with the character of the ducati motor in general, where to say that tolerances are not tight is an understatement.

Very cool find about this motor. Maybe Taglioni and Ferry had a beer together at some tech conference?
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Old 02-21-2009, 03:06 AM
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Quote:
Originally Posted by Bill in OKC View Post
from babelfish:
"the invention refers to a valve gear for high-speed internal-combustion engines with which the opening movement of the valve by one with a cam co-operating rocker finger is reached and close movement effected via double-armed levers, which attack at the valve and co-operate with cam discs"

It kind of sounds like it is describing a desmo valve train. The finger sounds like a normal rocker arm and the double armed lever sounds like the closer arm on a Ducati. Without valve springs there is very little internal friction loss in the valve train. A Ducati engine can be turned over very easy by hand with the plugs out because there are no valve springs to compress. The positive valve closure allows the racing Ducatis to spin much faster without the need for pneumatics. The biggest Ducati disadvantage is the difficulty in setting the very exact valve clearances.
There are valve springs in Desmo engines. They're just very light springs since the only pressure needed is to keep the valves seated during combustion. I don't think Desmo engines would be very good solution because of the inherit increased cost of valve train adjustments in terms of time and frequency. The other problem is with the increased mass of valves in the larger displacement engines. Ducati drove itself nuts trying to find vendors who could satisfy their needs on chromium plated cam followers.
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Old 02-21-2009, 06:14 AM
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Quote:
Originally Posted by WERK-I View Post
There are valve springs in Desmo engines. They're just very light springs since the only pressure needed is to keep the valves seated during combustion. I don't think Desmo engines would be very good solution because of the inherit increased cost of valve train adjustments in terms of time and frequency. The other problem is with the increased mass of valves in the larger displacement engines. Ducati drove itself nuts trying to find vendors who could satisfy their needs on chromium plated cam followers.
Yes the cost of valve train adjustment is a problem. Ducati makes 600cc cylinders (a 1200cc V-twin) so 6 of them would make a 3.6 liter engine - valve size doesn't seem to be a problem. The the NA 1200cc makes ~180hp stock. If you could bolt 6 of these cylinders together - hmmm around 540hp? The new motors are pretty reliable. Not an engine for the grocery getter though.
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Old 02-21-2009, 07:34 AM
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Quote:
Originally Posted by Flieger View Post
The 753 was the 1.5 liter flat-8 from the 804 F1 car. I never heard of that engine having desmodromic valves. Ludvigson's book called them "finger followers" but never mentioned "desmodromic". I also thought springs were involved. The only cars I know with desmodromic valves are the 1955 Mercedes Silver Arrows 300SLRs like what Fangio drove in F1. Straight-8 cylinder, MFI, great cars.

I always though Ducatis were interesting for those desmodromic valves. They have advantages and disadvantages, though. They are free-revving from low rpm but the power required to drive the valvetrain increases with speed, unlike the fixed-spring pressure systems. This means that the desmo eventually will have more power used to drive the valves at the same speed as a spring setup.

However, the desmodromic setup has much less valve float, provided you can keep the valve in complete sealing contact with the seat through careful maintainance of the closing cam tolerances and adjustment.

I do not know of any Porsche engines built with desmodromic valves, though I would be interested to see photos showimg otherwise. I would not be surprised to see drawings from engineering proposals from the Porsche engineering consultancy. The 916 and 547 four-cammers were complex enough to work with air-cooling. I do not think desmo would fit the air-cooled architechture without significantly re-engineering the design of the basic Porsche engine principles.
And by "much less valve float", you mean none...If the valve is mechanically opened and closed, the only way you can have valve float is through catastrophic failure of the valve train. While a desmo valve train does need to have its mechanical clearances maintained, its advantage is no valve float at high rpm. Like all things mechanical, it does have its limitations.
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Old 02-21-2009, 07:55 AM
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Anyone know anything else about this engine?

m110,

It looks like this was an experimental design and never used in GP racing. Desmo valvetrains go back to the 1914 Delage, and were invented because of coil spring limits. Even the BRM V-16, and GP bikes used hairsprings into the 50's because coils were a limit. The Porsche 804 was not competitive with the Conventry Climax V-8, so they were looking around for more power, and this may have been one proposal. This was right around the period when Honda proved the four valve pent roof (which goes back to 1912) superior to the two valve hemi and Conventry Climax and Ferrari were well on that road, which would make an aircooled GP engine obsolete. The four valve pent roof was put on the back burner for 40 years by the 1923 FIAT supercharged hemi, which was copied by Miller, Alfa, Bugatti, et all, until the supercharger and exotic fuel bans brought it back.
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Old 02-21-2009, 08:08 AM
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Quote:
Originally Posted by WERK-I View Post
Ducati drove itself nuts trying to find vendors who could satisfy their needs on chromium plated cam followers.
Actually, Ducati screwed the pooch by subcontracting the hardfacing on the opening and closing cam followers which led to premature flaking of the hardfacing. For the years Ducati was in denial, while smaller shops were making a mint by grinding off the crappy chrome, and inlaying colbalt or stellite hardfacing. To exaserbate the problem, Ducati's cams kept getting more and more aggressive with more drastic drop ramps from max lift points of the cam. This literally beat the snot outta the hard chrome areas of the openers and closers.
All the bad PR eventually forced Ducati to rectify the flaking chrome issue.
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Old 02-21-2009, 08:09 AM
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Quote:
Originally Posted by psalt View Post
Anyone know anything else about this engine?

m110,

It looks like this was an experimental design and never used in GP racing.
I would tend to disagree. It appears that the 753 was used in the 804 chassis that was in fact Porsche's only GP win ever (Gurney, France, Chassis #1 1962) from "1 1/2-litre Grand Prix Racing" By Mark Whitelock.
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Old 02-21-2009, 09:40 AM
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m110,

That would not be my guess. Take a look at Ludvigen's "Excellence Was Expected", pages 265-287, where he chronicles the development of the Type 753 engine. It clearly shows the three diferent cylinder head designs used and all of them have coil springs with finger followers. The final version with 72 degree valves had new follower pivots which "would have also been suitable for use with desmo valve gear". Even the final coil spring version of this engine was never used because Porsche dropped out for competitive reasons.

You also might take notice of the fact that in the final GP race of the Type 753 engine, the US GP in Watkins Glen, Gurney was running third when he faded to fifth due to.......... two broken inner valve springs.
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Old 02-21-2009, 12:13 PM
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Quote:
Originally Posted by psalt View Post
m110,

That would not be my guess. Take a look at Ludvigen's "Excellence Was Expected", pages 265-287, where he chronicles the development of the Type 753 engine. It clearly shows the three diferent cylinder head designs used and all of them have coil springs with finger followers. The final version with 72 degree valves had new follower pivots which "would have also been suitable for use with desmo valve gear". Even the final coil spring version of this engine was never used because Porsche dropped out for competitive reasons.

You also might take notice of the fact that in the final GP race of the Type 753 engine, the US GP in Watkins Glen, Gurney was running third when he faded to fifth due to.......... two broken inner valve springs.
That makes sense, I suppose this was merely a design plan...interesting nonetheless that Porsche had it fingers in so much R&D at that time. I have never heard of them actually building an engine with that valvetrain which prompted the thread. If anyone has the chance to get close to a Mercedes W196 or 300SLR inline eight with MFI and desmo valves it is quite a noise....a Porsche flat eight desmo MFI would have sounded even better.
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Old 02-21-2009, 12:26 PM
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Quote:
Originally Posted by Bill in OKC View Post
from babelfish:
"the invention refers to a valve gear for high-speed internal-combustion engines with which the opening movement of the valve by one with a cam co-operating rocker finger is reached and close movement effected via double-armed levers, which attack at the valve and co-operate with cam discs"

It kind of sounds like it is describing a desmo valve train. The finger sounds like a normal rocker arm and the double armed lever sounds like the closer arm on a Ducati. Without valve springs there is very little internal friction loss in the valve train. A Ducati engine can be turned over very easy by hand with the plugs out because there are no valve springs to compress. The positive valve closure allows the racing Ducatis to spin much faster without the need for pneumatics. The biggest Ducati disadvantage is the difficulty in setting the very exact valve clearances.
Yes, at low rpm the desmodromic system requires less power but the power required curve is second-order or exponential- it goes up increasingly fast with rpm. A spring system is constant power required. There was a good article a few issues back in Racecar Engineering Magazine.

Desmos can have some float- maybe slop is the better term- if their closing cam/rocker/valve tolerances are not perfect.

I have never heard the term "desmodromic" used to describe the 753 engine's valves. I have only heard of the "finger followers" which I never quite understood the significance of. The diagram does show a desmodromic setup, but I think the engine as actually raced had springs. The "finger followers" appeared to me to be a way to present less inertia to the cam and valve actuating.
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Old 02-21-2009, 12:28 PM
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I have only heard of the "finger followers" which I never quite understood the significance of. The diagram does show a desmodromic setup, but I think the engine as actually raced had springs. The "finger followers" appeared to me to be a way to present less inertia to the cam and valve actuating.


Yes, less inertia, more freedom in spring selection without the confines of a bucket tappet, and adjustment without removing the cams. Honda used them in their F1 engines before the development of pneumatic valves in 1991.
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Old 02-21-2009, 12:45 PM
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