DESMO Discussions (continued, here) Thread

[Harvey]

by LaceyDucati » Thu Mar 14, 2013 10:51 am

Hi again.

Firstly Harvey my comments were not in any way directed at you, only from my observations and experiences in life and from competition. I have no doubt that there are many engineers out there with greater knowledge than myself who could extract more power from a particular design. I have looked at a few modelling programs and I would agree that they are very interesting and useful for starting points. Thank you for the link. But my research back ground tells me that computer modelling is limited as I am sure you know. There are certain details that are very sketchy in the programs I have seen. They assume certain aspects of things like port shape and position being ideal etc. My opinion is that there is a point when theory has to stop and reality with all it's real world imperfections takes over. Flow bench testing and dyno work will then give more information as it is far more specific. Concerning books I think we have a similar collection!
Sorry if any of my comments have been taken the wrong way. Again another example the limit of the written word to to transfer full meaning and intent!

Thanks Nigel, I guess that I have come to expect some flack in some forums when I post some tech info, seems to make me the target of, “lewd comments”.

I became interested in the program modelling after I could not work on, or ride, so unfortunately I cannot put the theory into practice anymore. But it keeps the interest up,
Cheers Harvey.

[Harvey]

"The pictures of your angled inlet port save a lot of writing. "

Hello Harvey,
If your comment is, I assume, refering to the inlet port on the RT head, the steel manifold seems to me to be more of an issue with its sharp edged curve?
But this port and manifold would be needed to fit the engine and carb into the frames that were used. Keeping in mind that these bikes were not built for racing only.

Regards
Graeme

Yes Graeme I was referring to the angled port. Yes it is more for racing than road work. But it gets around the problem of the inlet port looking straight out the exhaust port, where a lot of the inlet flow goes.
On the standard head you can't raise the top of the port to redirect the flow down the bore as it weakens the valve guide support.
So you can only do the best you can to smooth the flow, and do a good job of the throat and seat area.
To keep it standard looking, you are stuck with the 29mm carb, which limits the top end breathing that you can get.
A cam that has more lift, without a lot of duration will suit, to get a bit more torque through the rev range, without loosing the bottom end torque that the RT is used for.
Cheers Harvey.

[graeme]

Hello all interested,
I started a new thread re better breathing for singles. Hope this is sufficient.
It interests me to see how other people do this,
A picture tells a thousand words the saying goes,
People here have lots more knowledge than me and it would be good to learn from you
if no one is interested the subject will fade away so I can't see any harm?

Harvey, you no doubt have lots of experience in your head, please pass what you can on so it doesn't get lost, (does that sound wrong? sorry if it does)

Graeme

[LaceyDucati]

From Bob

" Something I've noted-of before with those type mufflers, is the particular-design of the sound-absorbing/silencing-louvers... I believe the louver-openings within the replica-versions face the opposite-direction as those of the real Conti-mufflers (which thusly have THEIR louvers faced in the most 'streamlined' direction [for exhaust-flow]). _ And although I believe that that seemingly minor difference would indeed more-greatly interfere with otherwise less-disturbed airflow, (incidentally, not too-awfully dissimilar in manor, from that as I have proclaimed-of in my recently-mentioned excessively-higher valve-lift, result-expectation),, I would not have actually expected that airflow-interference difference to result with such a large difference in BHP (with a mere 350). _ But if there's no OTHER differences (in any of those muffler's dimensions), then there can be nothing-else left to suspect (for the power-output discrepancy, [expect perhaps things like atmospheric-pressure changes, if the tests weren't all done on the same day] ).
(This idea of louver-shape orientation possibly being responsible, ought-not be of any big-surprise to anyone who can conceive which way a 'funnel' should be faced in order to disturb "

Hi,

Just to confirm a few details. All the "silencers" had louvers cut in the same way around, streamlined to the flow. There were other differences as follows:

Genuine Conti (best performing and mellowest sound) - Has a solid louvred baffle tube, seemingly split in the middle, I cannot confirm any further detail until I get an old one to cut up. The tube is a larger diameter than the header, so the header steps into the baffle tube. This is posibble giving a refected wave and in some way is contributing to the better performance. Obviously the baffle tube is larger and less restrictive which will also play a part. The gauge of steel is heavy and there is no absobsion element so any silencing is via gases entering chambers.

Stainless replica 1 (second best performing) - baffle tube is the same diameter as the header and is perforated with louvres punched into it. The gauge of the stainless is heavy and there is an element of packing in the last section of the silencer.

Stainless replica 2 - (worst performance and harsh sounding) - has a solid louvred baffle tube the same diameter as the header. Light gauge stainless and no packing.

It is probably fairly obvious from these descriptions to see why the Genuine Conti out performs the others, it's less restrictive. But it should be noted marginally quieter (quieter is a loose term when used with a Conti!) My initial reason for mentioning these differences was to highlight the need to be cautious when making choices, as from the outside all these "silencers" look much the same and are marketed as "Contis". From my race engine preparation experience, many seemingly minor or pointless tasks can when added up to make a big difference. If you troll around on a road bike using a fraction of the bikes performance most of the time, then yes most of this sort of discussion is irrelevant. As is porting, high lift cams, large carbs.........

Nothing much to do with Desmo cams, just clarifying my previous post.

Best Wishes Nigel