350 SCD

[MotoMike]

I have Ian Faloons catalog of Ducati Motorcycles. could it be correct that the wide case 350 SCD produced 41 horse at 10,000 RPMs??

[DewCatTea-Bob]

" could it be correct that the wide case 350 SCD produced 41 horse at 10,000 RPMs?? "

____ Perhaps Eldert may have a good answer to that ?
But I would not much doubt it, since horse-power is as much to do with higher RPM as with raw-strength -(torque) !
(Thus it's possible for a 250 to produce more 'power' at 10,000-RPM than a 450 at 5000-RPM, [even though the 450 makes about twice the torque of the 250].*)
(*Looking forward to any discussion that M.Mike starts on this!)


Dukaddy-DUKEs,
-Bob

[MotoMike]

I don't have the book in front of me now, but the 250 was equally impressive. with a 11000rpm figure. (38 horse maybe?). this is where the Desmo valve gear was earning it's keep I wager. 67-68, the others were still using hairsprings. Even if you had the spring force to keep them from floating at 11k, the power they would steal would be significant. I think I read somewhere that when Mercedes used the desmo valve gear they gained 30 hp that was lost in valve springs of the traditional system. But then I don't think Mercedes used any springs at all.

[DewCatTea-Bob]

" Even if you had the spring force to keep them from floating at 11k, the power they would steal would be significant. "

____ That's what I once thought was the MAIN-advantage of the DESMO-system for the std.production Duc-singles, (since the original valve-springs were already capable of handling normal engine-revs).
But actually, only during valve-float, do the springs not return-back the energy which they have (temporarily) taken. _ So the only real loss that the valve-springs have permanently caused, is the resulting added friction between the two rocker-arms' bushings & support-pins and follower-faces & cam-lobes, all of which is really not much to be concerned with actually.
(Sorry to once again pop-the-bubble for those of us who may be 'Duc.Single DESMO-worshipers'.)


Dukaddy-DUKEs,
-Bob

[MotoMike]

Bob
If I follow what you are saying, the energy taken to force the cam lobe up under the rocker against spring pressure is then paid back by the spring pressure after cam rolls over the top and the rocker now pushes the cam along returning the energy it stole on the first half of it's excursion under the rocker arm? Ha you did it to me again.

Ok for the Ducati Singles which used the valve springs and the desmo. Though this is true I suppose, seems any system that can avoid having to expend effort in the first place only to have it returned less friction, would be more efficient and smoother running. Why didn't Ducati use a very light valve spring in their early desmo singles? It almost seems like your explanation has Ducati Single Desmo which is operating in the region that would cause valve float in a spring motor is the least efficient of all possible situations. because now do you not only have a spring not returning energy it stole during the opening sequence, but stealing more energy because the desmo closing action must snatch the valve spring away from its inertia driven float and pull it back along with the valve. Maybe so but I guess they didn't float...

And in the example of the Mercedes which did not use springs at all, where did the additional 30 hp come from if not the absence of valve springs. I know, now I will have to try to find that source, but I know I read it somewhere.

and in the newer generations of Ducati's don't they have very light helper spring to seat the valve with very little pressure exerted?

Mike

[LaceyDucati]

A Guy in the Uk I know has a 350 SCD & has Dyno'd it at over 40BHP, So yes this I true. The bike was featured in a recent issue of Classic Racer.

Nigel

[DewCatTea-Bob]

" the energy taken to force the cam lobe up under the rocker against spring pressure is then paid back by the spring pressure after cam rolls over the top and the rocker now pushes the cam along returning the energy it stole on the first half of it's excursion under the rocker arm? "

____ Well basicly, yes,, cuz it's established that energy is not lost (just converted), and the springs just store it until it's released and where else (friction aside) could that stored energy go? _ (Ever notice that the engine will often still continue turning somewhat longer, even after you've already discontinued working the kick-lever?)
Although I must agree however, that as revs increase towards the point where valve-float would occur, I can't see how the pay-back could still remain as great as the theft. _ So that which is not paid-back, must be absorbed into the increased acceleration of closing the valve.


" Ok for the Ducati Singles which used the valve springs and the desmo. Though this is true I suppose, seems any system that can avoid having to expend effort in the first place only to have it returned less friction, would be more efficient and smoother running. "

____ I'm not too clear on any point made here. _ If there indeed is one within that wording, then could you please state it in other words?


" Why didn't Ducati use a very light valve spring in their early desmo singles? "

____ Well they actually did ! ... The DESMO-singles were stock with the same weak valve-springs as used for the 160-engines.


" It almost seems like your explanation has Ducati Single Desmo which is operating in the region that would cause valve float in a spring motor is the least efficient of all possible situations. because now do you not only have a spring not returning energy it stole during the opening sequence, but stealing more energy because the desmo closing action must snatch the valve spring away from its inertia driven float and pull it back along with the valve. "

____ (First I must say that anyone who follows all that wording is someone who hasn't lost their sense of reason due to today's simpleton chat-type writing ! _ Good for you !)
__ Anyhow, all that could possibly be all correct IF the (actually employed) valve-springs were in some way attached through to the closing-rocker's action, (they're surprisingly actually not tied to the actual closing-system parts!). _ And since the actual employed springs are even weaker than that of a standard "spring motor", the spring float-point is at an even lower RPM,, and so if the springs were indeed tied to the valve-keeper/tie (also, along with the valve), THEN the DESMO-system (at top RPMs) would have to not only pull-close the valves but also have to push-open the valve-springs as well, both tasks at the same-time, of course !
I've wondered myself about how the weak-springs are actually doing in there,, whether they just on their own (during the higher RPMs), are still able to keep-up (well enough) with their (intended) spring-tie ? _ I must assume that they have to, in order to remain kept in their place.


" And in the example of the Mercedes which did not use springs at all, where did the additional 30 hp come from if not the absence of valve springs. "

____ Well as I had meant to convey previously, HorsePower can be gained from mere additional-revs, therefore the 30-HP might not have come from any more available torque (due to any lack of having to overcome resistance), but rather just higher RPM, (which their desmo-system may have then allowed).


" in the newer generations of Ducati's don't they have very light helper spring to seat the valve with very little pressure exerted? "

____ Yes that's true, and they're relatively super-weak, just for making starting more certain.


DUCATIly,
-Bob

[MotoMike]

" " Ok for the Ducati Singles which used the valve springs and the desmo. Though this is true I suppose, seems any system that can avoid having to expend effort in the first place only to have it returned less friction, would be more efficient and smoother running. "

____ I'm not too clear on any point made here. _ If there indeed is one within that wording, then could you please state it in other words?


DUCATIly,
-Bob

Yeah, sorry about that Bob. I was pressed to go somewhere and hurried through that without editing. All I was trying to say was that it’s more efficient if you can avoid the losses even if you get some returned. I guess it is odd to talk about smooth efficiency in a Ducati Single.

[DewCatTea-Bob]

" All I was trying to say was that it’s more efficient if you can avoid the losses even if you get some returned. "

____ Well actually, I had indeed picked-up on THAT part/notion of the wording,, it's just that I had assumed that with all the other added wording which was also included along with that particular notion, that there must be more to it all than just that, which I must've not been following entirely.
I'm now realizing that the first-part of the quoted-wording was likely in reference more so to your previous (& unquoted by me) wording, rather than the later-part which I lumped it with.
__ Anyhow, concerning the part you've clarified, I now certainly realize the point that you must've meant to convey,, and also, it's quite certain that bevel-gears would agree that their life is very-much easier -(less hectic!) working a DESMO-head !!


DESMO-Cheers,
-Bob

[MotoMike]

A Guy in the Uk I know has a 350 SCD & has Dyno'd it at over 40BHP, So yes this I true. The bike was featured in a recent issue of Classic Racer.

Nigel

Nigel
I looked at Classic Racer's site. they have an index of the current issue Sep/Oct 2010 and list a 350 desmo, but aren't clear if that is the one you are talking about. Is it? I might get that issue to see how I like it. kind of pricey over here.

regards,
Mike