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PostPosted: Sat Sep 17, 2016 11:46 pm 
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I was putting this drawl off until I could post pictures of the lovely bit of metal, but I failed to post them again. :roll: I guess that means I will have to fall back on my descriptive powers (sorry maz lOl ). If anyone wants to see pictures you will have to pm me your e-mail.

While my City x was apart having it's motor overhauled by Maz, I could then see into the standard header pipe, and it was not pretty. It looks like all show and no go where the twin pipes converge at the weld. maybe this is behind the stalling gasses of my 9 at low rpms....or not. Certainly this area of the pipe and down to the curve inside the muffler seems to be sensitive to any changes as I found by making a 'venturi' in the entry to my Stealth. Having changed to a 12R muffler, which is both reasonably quiet and yet less restrictive than the standard 9's, I wondered if fabricating another more subtle venturi effect device downstream of the converging header could create a beneficial effect. NB 08 and later models need not apply as the factory appear to have made their own 'flume' or flare into a wider muffler entry. Obviously any reduction will reduce maximum flow at this point and therefore power, but I'm interested in throttle response lower down.

I started by measuring the straight between the headers convergence and the start of curvature in the 12R muffler. This was 63-65mm with an approx diameter of 46mm. I ordered a length of 304 stainless pipe from Metals4U. The nearest od is 48.3 and I went for the thickest wall of 3.7mm to give some meat to work with. These lengths come at 250mm so I could make 3 experiments from a section.

A local engineering firm who specialise in stainless and 1 off specials turned the pipe down to 46mm od. I then started grinding and flapwheeling one end to make a tapered inner. I had read somewhere way back when that an entry of 15 degrees and an exit of 7 degrees was the optimum shape. Whatever, it's good to aim for something. Stainless is hard work and my one larger silicon carbide wheel took a beating. So I could have asked the engineers to turn the job out for me, but I wanted to see how the shape formed and stop when instinct stepped in (enhanced eddy at work lOl ). When the shape was close to looking right I made a longitudonal cut in the section of pipe. This 'springs' the pipe open to leave an expansion gap and ensured a tightish fit inside the standard exhaust.

Turned down to a 46mm od the wall is now 2.55mm and after polishing out with a flap wheel the min internal diameter was 42mm or a tad less in the centre section tapering to knife edge ends where the insert will mate with the standard exhaust. As the steeper entry is at the top near the header the narrowest part of the venturi is also towards the header.

The beauty of this length of section is that it covers the open joint and step where the header slots into the flared joint in the muffler. Hopefully there is a gain here. I tapped the finished section into both the header and the muffler to check the fit and it was good with an almost seamless flow from the knife edge into the existing curves. ;)

For fitting I coated the stainless section with copper grease to ease removal if required. Assembly was straight forward and it all slotted in perfectly. As it happens there is a slight taper in the header straight and muffler, which naturally stop the insert from pushing further in or moving out of position in use.

My trial run of 40 miles showed immediate promise. Once warmed up there was an urgency or ease of running as if the motor needed less throttle to move and the power was smoother over 1500 to 4500 or so. As you would expect there was a subtle loss of urgency as revs climbed, but as the miles went by even that started to change as if the ECU was adjusting itself slightly.

It's too early to gauge all of the pros and cons, so I'll do more miles before deciding whether to leave it in or not. The only downer at the moment is that that lovely gruffly sound I get from the motor when loading the throttle (and stalling gasses?) from 2000 rpm is not there. It just seems to flow seamlessly. :)


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PostPosted: Sun Sep 18, 2016 10:04 am 
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Reading this again in the fresh light of day, I forgot to mention that the insert section was cut to exactly 63mm in length. :oooops:

The section of the venturi as seen side on in the expansion gap still has a bit of a circular curve. I think that the exit taper should be a bit longer and constant to give the pressure wave a smoother exit (like a basic rocket nozzle ;) ). Vague memories tell me neck of the venturi should be only half the diameter or 21mm, so a bit more filing to be done. ;)


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PostPosted: Mon Sep 19, 2016 3:02 pm 
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Current ride: 2004 Buell XB 12s
Location: Schoorl ,Netherlands
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The sound of a V-twin engine braking is music to my ears!!


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PostPosted: Mon Sep 19, 2016 3:03 pm 
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Current ride: 2004 Buell XB 12s
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The sound of a V-twin engine braking is music to my ears!!


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PostPosted: Mon Sep 19, 2016 3:05 pm 
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Current ride: 2004 Buell XB 12s
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The sound of a V-twin engine braking is music to my ears!!


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PostPosted: Mon Sep 19, 2016 3:06 pm 
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Current ride: 2004 Buell XB 12s
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The sound of a V-twin engine braking is music to my ears!!


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PostPosted: Mon Sep 19, 2016 4:00 pm 
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Pictures now available thanks brother in buells. ;)

Self descriptive really, but;

1/ blank tube after turning down to 46mm OD with 2.55mm wall remaining.
2/ a sketch plan section.
3/ section finished with entry to the right, identified by ring marks where tooling 'picked up' slightly during turning. I plan to take a flap wheel to the exit taper and take out that curve some more.
4/ a trial fitting into muffler. The ends were not finished when this was taken and some sanding is needed to take them down another 0.5mm or so to a sharp edge, as well as smoothing the whole thing out inside. ;)


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PostPosted: Fri Sep 30, 2016 1:26 pm 
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I had insert out again last week and sanded more metal out. Profile is now closer to my original sketch and........it is better now! :shock: Amazing how 0.5mm extra internal diameter, or straighter taper on the inlet and exit can make. Or maybe it's just getting back towards what it was like before I put the device in! lOl

The term 'stalling' of exhaust gases was probably wrong. Turbulence would be a better word. I noticed that the Quicksteel filler I used many moons ago was eaten away by 'cavitation', not break up from vibration.

Just had a TPS reset, and am about to change the oil again before a higher speed run. ;)


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PostPosted: Mon Oct 03, 2016 5:16 pm 
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Well, well! Had a really good ride on Sunday; a group ride-out for breakfast and onwards for some nice sunlit meandering country roads. You need to go on a good run to shakedown any tweaks or changes and my XB was getting a bit sooty/missy from too much idling and messing with things lately. I had also cleaned the K&N and rejigged the breathers to give it every chance. ;)

As to the ride; I have to say that I am well happy with results of my venturi experiment. I should also qualify that in terms of how my bike was before fitting. On a 200+ mile ride into Wales earlier this summer I had been caught off guard by how well my 9 was running after Maz’s rebuild. On that ride while overtaking some cars, I realised that there was more road and power in hand to bag another car. Winding it on I was almost caught out by a big rush towards peak torque. Now with my insert, it is different, maybe to the extent that ‘less is more’? :shock: Horsepower fiends will be horrified, but there is a new quality of speed! After a long run I opened it up on a deserted stretch (a private and disused airfield runway lOl ) to briefly meet a barrier of sorts at 5,350 ish. Work that out, but it seems there is a limit of how much gas will flow now. Whereas before there was less below that and more above. ;)

To me the XB9s feel they have a more mechanical link between the throttle and the back tyre than a 12. Fitting a 12R muffler to my 9 took that away and made it more 12 like, but the venturi has brought more of a direct link back to the throttle and then added other benefits. The thing runs like a train from 1500 to 5300 with seemingly effortless response. The deeper exhaust note is also back after sanding the insert out some more. The torque feels super smooth to the extent that I don’t miss the higher power. Winding it on hard from 2500 now can yield a surprisingly rapid pick up with a fruity exhaust note, which tells me the new ‘choke’ is evacuating the pipe header much better in the lower part of the rev range. Top gear now feels lower in the same way as my enhanced Stealth used to. I was in a very happy place just breezing around and past slower cars with no effort and torqueing out of bends. 8-)

If this sounds positive, I would be interested to know how such a device would work on a pre-08 XB12 possibly with the exhaust valve servo disabled.


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PostPosted: Wed Oct 05, 2016 5:37 pm 
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Conclusions and plans:

it looks like l spent around £40 and a week of my time making my bike slower, but within my own set limits l think that l can actually ride this thing quicker now. ;)

I don't want to change the current insert in case l lose some of the effect. I still have enough tubing to make two more shapes and l have one in mind, but this is a bit like trying to reset a broken leg (God forbid) with pain killers. What the XB really needs is a better design and build set of headers rather than flashy looking mufflers. If you look at a specialist race header the siamesed section flows seamlessly from 2 into 1 without any surplus volume (Look at the RB Racing web site). If the cross section of the intersection exceeds that of the two incoming pipes then logically the gasses will slow. Of course Buell knew this and there might have been a prototype 9 that actually made 92 bhp or more, but cost of producing such a header may have been a problem or that motor may have exposed other weaknesses? Does anyone still have a close up picture of a prototype?


Until then l could get a spare set of headers, cut off the siamesed section and try to fabricate a more streamlined effort. ;)


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PostPosted: Sat Oct 08, 2016 1:15 pm 
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I realised that there are more than 'RB Racing' sites on the web. :roll:

This is the US one. The various pages also provide an entertaining read. ;)

https://www.rbracing-rsr.com/lsr21.htm


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PostPosted: Sat Oct 08, 2016 1:18 pm 
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'1' :coat:


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PostPosted: Mon Oct 10, 2016 4:08 pm 
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These 'RB Racing' pages in particular, which I used to find easily, but are now buried in there somewhere; ;)

https://www.rbracing-rsr.com/exhausttech.htm


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PostPosted: Mon Oct 31, 2016 5:00 pm 
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Current ride: XB9SX
Weather Report;

I thought I would do a quick update on recent atmospheric effects on my exhaust experiment.

As summer seems to have ended now, cooler denser air has entered the mix. I noticed that where the air pressure is high and dry the venturi effect can take on a slightly 'relentless' feel (a bit like these threads lOl ) on part throttle. It's only a subtle effect, but one could compare the motors pulsing to listening to a live rendition of Kraftwerk's 'Robot', whereas I prefer to listen to the more harmonic sounds of 'Endless' from TEE. Well I did say it went like a train! :D :D

Moving into moister air this relentless pulse effect eases and if anything, and the engine feels stronger with a fat spread of torque (well it is relative) extending to around 90 or so. It's been more fun pulling away from traffic lights since the venture went in, but I still think the plumbing could go wider. I guess the next move has to be another experimental insert with less restrictive neck to the venturi for winter use, so I am currently making one with 43 and a bit mm narrows for colder conditions instead of the current 42 and a bit mm. It's a 5 min job to swap inserts as I would normally be taking the muffler off to coat it with S100 anti-corrosion spray at this time anyway. ;)


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PostPosted: Mon Nov 14, 2016 2:31 pm 
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Part 14 of this post to myself, or a warning in case anyone else is mad enough to copy this experiment. lOl

After a combined run mpg check, my 9SX is now averaging 5mpg less than before the 'venturi'! (54.6 instead of 59.5ish) :| Well I guess you don't get something for nothing. Difficult to be sure of the degree of change here as we are getting into colder air, although the denser air combined with enhanced exhaust scavenging is giving the '9' some actual bottom end stomp now. Think I'll just keep this insert in and save my grinding wheels. ;)

While it could never be described as being torquey or front end lifting like a 12s, when carving in and out of roundabouts yesterday, my usual amount of throttle had the chassis squirming or 'crabbing' off line in a way I am not used to at such low revs. NB all these conditions were noted after my usual 26+ mile warm up before exceeding 4k. 8-)

Perhaps I should also do a plug check, but they only went in at the rebuild 2253 miles ago. :?


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