Late model wide case exhausts

[machten]

This thread was born out of a discussion about camshaft changes in my 1974 450 Mark 3, which can be seen here…http://www.motoscrubs.com/forum/viewtopic.php?f=3&t=1895

A question has arisen where my ’74 450 Mark 3 when fitted with the hotter 350 Green & White camshaft (rather than its factory stock mild 250 Scrambler White camshaft) and what I believe to be a stock Silentium exhaust, seems to bog down and in fact miss just north of about 4000 RPM.

This raised the following related points from the earlier thread…

Kev: " One thing I have tried as an experiment was to put the Silentium back on with the G&W camshaft. Forget it. It won't run over 4000 RPM. "

DCT Bob: ____ I'm left to assume that the particular "Silentium" which you're meaning to refer-to is actually the shorter/stock Scrambler-style version, correct ?
If so, then there's something-else wrong if you actually literally meant that "it won't run over 4000 RPM",, so I rather assume that your must really mean that decent acceleration falls-off after that RPM.range, thus making that muffler/cam.model-combo to be pretty-much worthless.

Kev: No. I'm referring to the long one standard on the later Mark 3s (see picture below). I can't recall the IGM number off the top of my head. Before I put in the G&W camshaft, my original one had the rear baffle taken out, but it was starting to get a bit rattly and I had a new one around, so I installed it early last year. This still has all its baffles complete. It worked OK with the White camshaft although I'm sure it was restricting even that performance. With the G&W camshaft installed with the "new" Silentium, just over 4000RPM the bike will start missing (as in not firing). If I put the Conti style exhaust back on, no problem. I haven't tried the old Silentium with the final baffle removed.

DCT Bob____ I've unfortunately never had one of those newer Silentium-models to have ever examined. Do you know for-sure whether it's any more heavily baffled than the pre-1971 version ?

DCT Bob:____ That seems highly odd ! _ So I still think something-else has to be contributing to that strange result.
Is that not the same Silentium-model employed on the later 450M3D.models ?
In any case, it would be of keen interest to see what result would be found with that very-same muffler installed on the 450-DESMO !
And if & when it's found that the results of that test is-not the same and rather as normally expected, then you'd know for-sure to suspect that there's indeed another factor that's contributing to the over 4-grand strangeness.

These questions prompted me to do a bit of looking around. I hadn’t found it easy as I couldn’t seem to find a Parts Manual on line that includes the late model exhaust systems. After much hunting around, I finally found one covering up to the 1973 models and printed in 1974.

As I understand it, Sil Motor produced two structural versions the later Silentium long silencer. The first one was a two piece tube consisting of the primary baffle and a separate slice encapsulating a secondary baffle, joined together with the use of a ring clamp. You can see that here in this Ducati brochure for a front drum brake Desmo. :

.

I am uncertain of the IGM (Ispettorato Generale Motorizzazione) number on these as I don’t have one.

Later, Sil Motor produced for Ducati a slightly different construction silencer which was one piece although still with a separate primary and secondary baffle. See below my 74 450 Mark 3 which is labelled “Moto Ducati I.G.M 1984 S”. I have two of these, one of which was in its original sealed packaging with 40 year old company packing tape, so I am confident of its provenance.



Regarding the baffling (no pun intended!) question raised by Bob…if you look at these pages from the parts manuals, it’s not really clear to me what they are saying as to specific exhausts for different Ducati widecases. Note for instance 0615.84.105 is referred to as a Tromboncio rather than a Silenziatore. Any significance in that?









To add to the confusion….as I said, I have 2 Silentium Moto Ducati IGM 1984 S systems. Their secondary baffle is different. The old one that came with the 450 when I got it:



And the until recently unused one out of the factory packaging:



Can anyone throw any light on all this? It's primarily for interest, as I am most likely to continue running the 450 with a Conti replica style pipe anyway as the performance is much improved with it and the Green & White camshaft working in concert.




Kev

[double diamond]

Kev,
Of course, the “Tromboncino” is the race kit megaphone and affords no silencing whatsoever!
Looks to me like your original silencer end has been punctured in a few placed to add additional outlet area. Depending upon the internal design of the silencer, this may have had little to no effect. Without the punctures, the end caps are basically the same.
Matt

[DewCatTea-Bob]

[quote= machten ...
" Sil Motor produced two structural versions the later Silentium long silencer. The first one was a two piece tube consisting of the primary baffle and a separate slice encapsulating a secondary baffle, joined together with the use of a ring clamp. You can see that here in this Ducati brochure for a front drum brake Desmo. "

____ That one appears to be the Silentium-model that was employed prior to 1971 on all DESMO-models (except the cone-cap was hollow & didn't contain any baffle [at-least for the USA]).



" Later, Sil Motor produced for Ducati a slightly different construction silencer which was one piece although still with a separate primary and secondary baffle.
I have two of these, "

____ The pic.quality of the example on your 450Mark-3 wasn't good enough for me to see for-sure, but it did appear to be missing a ring-clamp,, yet I gathered that it couldn't possibly be a "one piece" construction, since you've stated you had removed it's secondary-baffle.
__ So how's it possible that any baffle could've been removed, if the main-body is indeed a single-piece construction ?
I've never seen one of the secondary-baffles entirely itself,
can you post a picture of the unit you removed ?



" Their secondary baffle is different. "

____ How so ?
Is the newer version removable as well ?



" 0615.84.105 is referred to as a Tromboncio "

____ When I ordered that part-number (for a 450) from Berliner, the shorty-megaphone I received didn't look exactly like that drawing, cuz the ratio of length to diameter was obviously not the same, as the actual length was a few inches shorter.



" I am most likely to continue running the 450 with a Conti replica style pipe anyway as the performance is much improved with it "

____ As good as you find the performance to be with that, you'd no-doubt be even more excited with a meg.shorty !
__ An ex.header extension-pipe is also pretty-impressive as well.
I can understand you not caring to try-out a vacuum-cleaner extension-tube, but a new chromed drain-pipe (made for a std.sink-drain) really doesn't look too bad and can be fitted well enough. _ And the experience you'd gain, alone,, is worth the mere cost of the 8 to 14 inch long piece of drain-pipe !
The Conti is a showroom piece,, so for the sound-level, try the more performance-functional straight-pipe and forget the 20-pounds of mere beauty.


Duke-Cheers,
-Bob

[Harvey]

Giday Kev, stick with the Conti rep. its the best set-up for a road going 450. I have used that one on all the developments of my 450. It lets the exhaust system work to drop gas pressure and allow the sound waves to operate across a wide rpm range.
This is with a 32mm, and a alloy ram tube, with that exhaust, probably the best you can do with a standard engine.

This is with the full 456 engine, 41mm Malossi, V2 cam, and that same exhaust.

[graeme]

I found that a Conti type works the best also.
This engine with standard desmo cam, 42mm inlet, standard exhaust valve, 87mm piston and a 36mm carb.
Tried 40mm but too big for a (this) engine.

[Dave450]

Yes, a Conti is the way to go with a street 450. This is with a 40mm, race cam, 42 mm inlet, std exhaust. It gives a nice spread of power in the mid-range - great for the road. You will sacrifice top end a bit, but I don't know of any underslung road silencer that doesn't. I haven't tried a Supertrapp, though. Has anyone else?

Nice pic of you, Graeme! And Silver Shotgun looks good, too.

[machten]

____ The pic.quality of the example on your 450Mark-3 wasn't good enough for me to see for-sure, but it did appear to be missing a ring-clamp,, yet I gathered that it couldn't possibly be a "one piece" construction, since you've stated you had removed it's secondary-baffle.
__ So how's it possible that any baffle could've been removed, if the main-body is indeed a single-piece construction ?
I've never seen one of the secondary-baffles entirely itself,
can you post a picture of the unit you removed ?

Bob...The secondary baffle is held in by three screws as you can see below. I had a quick go and undid them. If it just fell out I'd have taken a pic of the baffle, but it didn't and I don't have something I can easily use as a 3 foot drift, and didn't want to stuff around afterwards trying to get the holes lined up again if it was a tight fit going back in.




The secondary baffle is different between the two "once piece" Silentiums I have. Have at look at the pics of the end of the secondary baffle.

Use the Conti style...(General thrust of comments)

Yep. No argument. I'm just interested in why I seem to have no choice. If anyone who's running the stock Silentium can take a pick of the business end of it and advise the IGM number, I'd be interested.

Kev

[DewCatTea-Bob]

[quote= machten ...
" The secondary baffle is held in by three screws
I had a quick go and undid them. If it just fell out I'd have taken a pic of the baffle, but it didn't "

____ Unless you had intended to pull the baffle from your 'new' Silentium as well, (to learn whether or not that would chance to cure your over 4-grand running issue),, I certainly hadn't any expectation for you to be bothered with any such attempt with your newer-Silentium.
I had just assumed that you hadn't lost the already removed baffle from your old/original-Silentium, and-so could rather take a pic of that-unit.
__ Anyhow, I now gather that the secondary-baffle is-not much like the primary-baffle. _ And-so it can be removed rather from the tip-end (instead of from within the main-body).



" The secondary baffle is different between the two "once piece" Silentiums "

____ Besides that secondary-baffle difference, do you think the new/replacement Silentium may have any other internal baffling differences that could also possibly contribute to the over 4-grand running-issue ?
Is there any notable difference in weight between the two Silentium-units (other than the weight-difference of the removed baffle), which may be indicative of differing/more-complex primary-baffling ?

Use the Conti style...(General thrust of comments)

____ I'm thinking that my related comments (possibly more-so than Kev's comments about choosing between his Conti-style & Silentium muffler-units), may have possibly inspired the 'weigh-in' on the choice-matter. _ And if-so, then I'm afraid my brash*statement concerning the Conti option may've been taken too seriously.
(* As it possibly may've been interpreted that I was actually meaning to imply that the Conti-style is so relatively heavy, that it should rather be relegated to show-bikes.)
However I-myself of-course also realize the sensibility of preferring the Conti-type mufflers (at-least for regular/daily road-riding) ! _ I had just basically meant to emphasize the impressive functional improvement of the meg.shorty & straight-pipe exhaust-alternatives over even the Conti-type ex.plumbing.
__ While I don't have any comparative dyno.figures to factually confirm so,, my good opinion is that the overall power-increase/difference which the Conti offers above-&-beyond the stock Silentium, is only 1/3rd to 2/3rds as great as the power-increase provided by the meg.shorty (over the Silentium) ! _ And-also, the straight-pipe offers an even greater peak-power (and more exciting power-delivery) ! ...

stick with the Conti rep.
It lets the exhaust system work to drop gas pressure and allow the sound waves to operate across a wide rpm range.

____ I understand what Harvey means...
For one-thing, the extended length of the Conti-style (along-with it's rather remote exhaust-outlet point) does indeed tend to assist low-end power-delivery,, and the outer megaphone-shaped casing would tend-to also assist power throughout the rest of the entire rev.range, (if the louver-baffling internal-construction didn't interfere with the purity of the pressure-wave workings that the megaphone-casing alone would provide). ...
I don't know what technical design-work is employed within the megaphone-case internals of the Conti-reps, but if their tube-throughway has any progressively larger diameter at it's outlet-end than at it's inlet-end, then the 'megaphone-effect' could still possibly remain fairly significantly effective (as Harvey has implied). _ But otherwise I'm fairly sure that the Conti-design's expected megaphone-effect must likely be near entirely baffled-away,, and-so then only still offers just the intensified momentum-effect (afforded by the extended-length), although even that beneficial effect is somewhat disturbed by the flow-impeding action of the ex.tube-length containing all the louver-baffling. - (BTW, concerning the 'Conti-replica',, does it's protruding flute-louvers face the same direction as within a real Conti, or rather towards the opposite way ? _ As I'd expect that having the louver-flutes streamlined [as like a fairing-windscreen] for ex.air-flow passing outward, would naturally be the most functional design.)
__ Anyhow, it's really premature to conclude that the straight-pipe alternative isn't worth a try-out just because ya already have the preferred/desirable Conti-style ex.outlet. _ Cuz a 'straight-pipe' rather doesn't offer any 'back-pressure' ex.flow-resistance,, and-so compared to any baffled-muffler, it rather tends to help the engine run more like as-if under the added effect of 'intake-boost' (with muffler included) !
I believe Harvey must already realize that the only performance-drawback to a 'straight-pipe' ex.outlet, is that it rather concentrates the full-effect of the helpful pressure-wave only within a relatively narrow-band of the entire rev.range,, but that's then well-above what would otherwise occur with any other ex.system, and the similar (but much reduced) effect likewise also afforded by a megaphone is rather minimally more performance-aiding/intensifying than the back-pressureless effect alone, (as the full-strength of the desired pressure-wave effect is then spread-out & diminished [so as to share portions over a wider rev.range]).
__ Ya just don't know what ya're missing until ya've tried a straight-pipe extension ! _ As ya otherwise can't fully realize what's being lost with whatever muffler ya're running.
Also, an ex.pipe extension-piece can be made to emulate the megaphone-effect by fluting it...
For example, an extension-piece I once had (on a 350) was slightly longer than 1-foot, and I fluted it by drilling four 10mm-holes (evenly spaced 90-degrees apart) 3-inches from the ex.outlet-end, plus six 7mm-holes (spaced 60-degrees apart) 6-inches from the ex.outlet, plus another eight 5mm-holes (spaced 45-degrees) 9-inches from it's tip-end.
Those three concentric rows of progressive-area hole-exits create (sufficiently spaced)
negative-pressure passageway-anomalies -(which actually provides a rather positive/beneficial power-enhancing effect [similar to that which the actual/final ex.outlet provides])- which each separately alter passageway-pressure, all of which in-turn work to virtually function much-like the megaphone-effect does, except with stronger steps (rather than a smooth-ramp, [so-to-speak]). _ The resulting four 'steps' (counting the main/final ex.outlet), function overall to yield pretty-much the same (if not stronger) beneficial enhancement-effect on power-production as does the desired function of the megaphone-shape (& it's ex.outlet), but without all the extra bulk/weight (that megaphones additionally require to be fully constructed).
__ I'll later add some more details concerning straight-pipe tuning, if anyone shows any further related interest.

I found that a Conti type works the best also.
This engine with standard desmo cam, 42mm inlet, standard exhaust valve, 87mm piston and a 36mm carb.

____ As proud as you must be of your modified 450's performance, Graeme,, I believe that if you installed your M1-camshaft into your 450-Scrambler and also attached an ex.pipe-extension (in place of the muffler),,
that not-only would you then find your 450Scr to be your funnest Duke to ride, but also if your identical-clone was riding against you on a tight/twisty race-course (where 1st.gear then gets more than it's share of use), I'd place my bet for your 450Scr to win the race far-&-away !!
__ You gotta try that combo Graeme, as then you'll become 'enlightened' about the actual relative short-comings of the Conti-performance craze.



____ I've added a couple adjusted pix below to provide (hopefully) improved*viewing of the displayed 450s.
(* A/B-comparisons viewed on MY monitor, reflect obvious improvement between these adjusted versions vs. the original pics.
If anyone sees otherwise, then please make me aware !)


Dukaddy-DUKEs,
DCT-Bob

[Harvey]

Sorry for the delay internet problems.

I understand what Harvey means...

Now I know Harvey must already realize that the only performance-drawback to a 'straight-pipe' ex.outlet, is that it concentrates the full-effect of the helpful pressure-wave only on a narrow-band of the rev.range,, but that's then well-above what would otherwise be occurring with any other ex.system, and the similar (but much reduced) effect afforded by a megaphone is barely more performance aiding than the back-pressureless effect itself, (as the pressure-wave effect is then merely spread-out & diluted [so as to share portions over a wider rev.range]).

Yes well no argument there Bob. I would say every body would have tried an open pipe at some stage, and there is no denying that if the length is set for the particular rpm, it will produce the most torque at that point, as the expansion of the sound wave, from the pipe to the atmosphere is as intense as you can get, so the negative pressure returned to the chamber on overlap, is also the strongest,,,,,,,, unfortunately the sound out the back is also the loudest.

As you say " it concentrates the full-effect of the helpful pressure-wave only on a narrow-band of the rev range".
Once out of that rpm range, it will start to work against the desired effect. If the maximum torque is wanted to appear at say 6500 rpm, then a pipe length from the valve to the expansion point would be about 41.5". So that is why the divergent cone on the end, is so effective, as the 41.5" can be in the middle of the cone, and the sound wave will expand all along the length of the cone, covering all the rpm lengths from the start of the cone to the outlet. Of course the intensity of the returned pressure is lower, but it is still effective, covering a wider rpm range.

I don't know what technical design-work is employed within the meg.internals of the Conti-reps, but if their tube-throughway has any larger diameter at it's outlet-end than at it's inlet-end, then the 'megaphone-effect' could possibly still remain fairly significantly effective (as Harvey has implied). _ But otherwise I suspect that the Conti-design's megaphone-effect is pretty-much entirely lost,, and-so only still offers the increased momentum-effect (afforded by the extended-length), although even that benefit is somewhat disturbed by the flow-impeding action of the ex.tube-length containing all the flute-baffling.

Looking at the design of the Conti there are the two different functions that have to be meet, the first is to allow the exhaust gas pressure 'plug', of about 70 psi, that is released when the valve opens, to run the length of the engine pipe, the inertia of that 'plug' pulling the low pressure in the cylinder around 60/70* ABDC, then to reduce the pressure quickly, as that gas expands into the volume of the cone, the main gas flow travelling straight along the center pipe.

The other function is to allow the sound wave to expand into the diameter of the cone, along the full length of the cone. The perforated pipe through the center is transparent to the sound waves, the sound passes through the holes, as it has no mass to restrict its movement. So the cone still acts the same as a cone without the center pipe. All this depends on how well the Replica is designed to meet those requirements.

[DewCatTea-Bob]

[quote= Harvey ...
" Sorry for the delay "

____ Thanks for your response-post Harvey ! _ I had been expecting that you might have something-or-another to comment on, (since I had once learned in the past that your level of understanding of such exhaust-tuning related tech.details is technically-superior to my own).



" Yes well no argument there Bob. "

____ Well that's quite an extra-relief to hear, Harvey,, as you've somehow quoted & responded to my original initially-submitted post-wording (that later became edited [with corrected/elaborated wording], nearly 2-days before your response-post became submitted).
I had felt the need to edit my original hastily chosen wording so that it would then make better sense and-thus be less likely to be misunderstood (and found fault with). _ So if you hadn't found anything to argue with concerning the old-wording you've quoted, then I'm now even more confident of my edited-wording !
__ I assume that by-now, you (as do many others), already realize that I most-often rewrite/edit my post-wording (and-also add extra wording) at later times (whenever I finally get-around to doing so). _ So I expect that you've some-time since already became aware that my post had become more elaborate, (even-though you've left no clue of having noticed),, as all my more fully edited posts are always denoted with 'DCT' prefixed to '-Bob'.



" I would say every body would have tried an open pipe at some stage, "

____ I'd agree that most everyone has tried running the engine without any muffler, just to hear it,, but I'd figure that about 1 in 4 have never actually ridden their Duke without any additional ex.plumbing added to the ex.header, and fewer-still who've gone-ahead & tried-out actually racing through the gears that way (so as to get a good feel of the stronger performance with merely-just the ex.header alone).
__ As a teenager, I used to race at a local 1/4-mile raceway with merely-just the stock ex.header, as the resulting high-RPM.power then felt much stronger. _ So I tried cutting-off a few inches from the header-pipe's ex.end to learn if the power-effect could be even further improved,, but the price of that naive experiment, cost the warping of the ex.valve !
That lesson was learned by shutting-down the throttle entirely closed with the motor left in gear at high-RPM (for engine-braking [after winding-out the gears] at the end of the 1/4-mile strip). _ Cuz without any added ex.plumbing connected to the ex.header, the shortened pipe-length was then no-longer able to adequately warm-up the cold-air that then became able to reach the ex.valve,, and-so the sudden temp.change across the ex.valve warped the valve-head angle (on the v.stem) just enough to allow sufficient air-leakage (past the valve-seat) to keep the engine from creating enough compression for kick-starting.
So ever-since, I've tried to avoid racing a hot engine with merely just a header-pipe (so-that I wouldn't have-to be concerned with avoiding cold-air reaching-in so deep towards the ex.port).
So I recommend that no-one else try cutting-off more than 2 or 3 inches away from the stock ex.header and run that way without any ex.pipe-extension add-ons.



" unfortunately the sound out the back is also the loudest. "

____ Of-course there's no denying that a straight-pipe allows the loudest sound-level, however according to my-ears, that sound is a lower-pitched report that's a bit more preferable to the ear than the higher-pitched bark that's emitted from (real) Conti-mufflers.
In other words, I-myself find that the slightly quieter noise-level of a Conti is-not really any more preferable than the slightly louder sound-level of a straight-pipe.



" As you say "it concentrates the full-effect of the helpful pressure-wave only on a narrow-band of the rev range".
Once out of that rpm range, it will start to work against the desired effect. "

____ Well Harvey, my-own understanding of the involved physics doesn't quite agree with your particular chosen-wording...
While of-course I certainly can't outwardly disagree with your use of the word "start", I do however tend to believe that your word "against", is fairly misleading...
If I had been the one who wrote such a statement, then I rather would've said the likes of: "Once 'off-the-pipe' and headed outside of that tuned narrow RPM-band, the neg.pressure-wave will then become ineffective (and neither help nor hinder, as the RPMs climb towards twice the tuned-RPM.band)." .
Cuz just because that pressure-wave becomes no-longer conveniently timed to arrive at the ex.valve during the valve-overlap phase, does-not really mean that it's effect then becomes functionally directly opposed to the standard Otto-cycle overlap-function and actually start to rather work "against" the exhaust cylinder-purging during other neighboring normal RPM.operating-ranges existing outside of the tuned-band, (as your posted-wording seems to imply).
I'd assume that if the normally desired pressure-wave effect ever actually became in true opposition "against" exhaust-flow out of the cyl.chamber, that it wouldn't possibly occur until perhaps when reaching TWICE the tuned-RPM.band,, and even then, it's (possibly)-oppositional effect-strength ought be significantly diminished at that midway-point (half-way back towards the ex.valve).



" The perforated pipe through the center is transparent to the sound waves, the sound passes through the holes, as it has no mass to restrict its movement. So the cone still acts the same as a cone without the center pipe. "

____ I suppose that could indeed be true, and I had even suspected so myself,, but I figured that the louvers partially covering all the flute-holes would pretty-much BAFFLE the sound-waves into such a fuzzy set of uncorrelated sound-wave reflections, that the desired sound/pressure-wave effect would thusly result with diminished pressure-wave intensity to've effectively become decimated-down next to near-nonexistence, (relatively compared-to that of a Conti-shell/case with no internal tube of flute-louvers).
So I think that the Conti-design's main contribution must rather be it's lack of significant back-pressure, much more-so than any residual megaphone-effect that it may still provide.


Dukaddy-DUKEs,
Dct.Bob