Having said that I was happy with my current exhaust insert (see earlier Venturi 2 thread), I started to question what had transpired, and how to take things to another level………..or back to where they should be!

‘V2’ as I shall now refer to, was producing a pleasing sense of ‘get you there’ urgency at all revs and at only part throttle. It’s as if the combustion process was constantly being ‘advanced’ in some way. There was a sweet spot between 3600 and 4200 or so and as you rode through this region of midrange (in spite of a healthy engine pick up) the exhaust note became a subdued thrumming. A bit like taking a freshly run in Honda above 5-6000 rpm for the first time……..NICE……. , but absent was the bad ass ‘BOOM’ we know and love in our Evo-X motor Buells. This alone suggests to me that the pressure wave, or wave pulse within the exhaust had shifted one way or another. Above 4200 and going open loop, the motor pulled harder and harder as you wound open the throttle to an addictive sort of beat from each power pulse, but there was no escaping the fact it all felt a bit ‘metered’.

In the above scenario the V2 sleeve insert when measured at regular internal diameters through its 62mm length from entry to exit was; 46 – 43 – 43 – 44.5 – 46mm. That’s a regular sided inlet cone, a parallel choke and a regular sided shallow angled exit cone. What I thought was needed was to open out the rear of the 43mm choke to increase the low pressure area in the exit. I decided on something nearer 46 – 43 – 43.5 – 45 – 46mm. This makes the exit cone more ‘bell shaped’ with greater volume (flared), but it is still an incredibly subtle change.

30 minutes later with an abrasive flap wheel and you would be hard pressed to see the difference, but by drawing the tube walls between a pinched finger and thumb you can definitely feel the shape. Once installed and after the magic 26.4 mile warm up, after which I can only guess that the air temp sender is nicely cooked, I was able to see the differences.

I was initially worried that I had opened things out too far and would throw away all that low rpm part throttle advantage, but nothing of the sort. The most important change was that the Buell’s characteristic ‘boom’ was back! It seems to combine all the power pulses into one homogeneous sound as if each exhaust pulse is complementing the other (in tune?). Whatever, the power surge when overtaking was more instant or explosive. It reminded me of watching and hearing the boom of a 6.5 litre V8 McLaren M6B blitzing the Silverstone Club circuit when I was a lad. That sort of thing stays with you, and maybe that’s why I love Buells.

I can only conclude that I had caught the 'wave' again! I was also starting to become concerned about directional stability as I passed cars winding it on in the oncoming lane. Maybe the tyres were under inflated, or maybe I am just getting old and infirm?

Nice

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Better to Burn Out Than Fade Away

In the garage -

2001 X1
KTM390 Duke
Ducati 950 Monster +
CCM Spitfire Scrambler

Surprising the subtle difference to tuned lengths or diameter, have on an engines performance and sound
Have or did the AFV values change once you are on the wave or fall off it?

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Buell Ulysses XB12X 06/08

why don't you speak to Albert666 (Alan) , who is APH exhaust
as your long search seems like the exhaust equivalent of alchemy

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Feros Ferio

Thanks for the positive responses. As for AFV....don't ask me as I wouldn't know! But seriously the V2 configuration did seem to get 'warm' (fan always on) and bothered in terms of fuelling in town, even with the additional 28 sq. in heat dispersing area to the oil cooler (maybe that only works out of town at speed?). Won't know until I get stuck in Bristol traffic again.
And yes I have spoken to Alan, but he quoted many variables, or is keeping the secrets of his trade close to his chest? Maybe when I am satisfied with a shape and fully understand it, I can commission a complete new header from him!

...or you could buy one from him, & study it
learning from the top of the tree , is better than scratching around in the dirt

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Feros Ferio

Returning to my exhaustive threads, l have managed to find a spare set of header pipes to continue my experiments thanks to brother in Buells.

If you recall, l had developed a Venturi shaped insert to fit between my XB9s header collector and the muffler to enhance exhaust gas flow. I first discovered this phenomenon when l shaped some metal filler into the neck of my Stealth muffler to smooth steps in the flow. I had formed a sort of flare or bell shaped entry to that muffler which resulted in a dramatic improvement in throttle response and associated sound!

When my ears started to give me gip, Andy on the recommendation of pash, l fitted a standard XB12 muffler. This gave a quieter exhaust combined with better top end rush, but a noticeably muted bottom end torque. Combining ideas from my stealth experiments lmhit on the idea of making a metal sleeve Venturi to enhance things. After 3 tries l arrived at the current Venturi shape. This seems to have brought the midrange torque rush down range by about 700 rpm.

In my previous threads l hinted at some directional stability issues during an overtake. I had put this down to my bad riding, but repeat scenarios have shown that this was a real effect. Late last year on a bright high barometric pressure day when pulled out to overtake some cars and apples a big handful of throttle on a slight incline, the bike crabbed towards the opposite verge. I had to roll off the throttle and straighten up parallel to the nearest car before l could open up again to complete the pass.
Yes l know that if you tried the same thing on a 12, it would just lift the front while cranked over, and you would have to shut off slightly. No my 9 will not quite wheelie on the throttle alone at that speed.

Still there is a strong surge at rpm that was not there without my Venturi.

My plan with the spare header was to have the Y collector cut off and one of improved shape cut and welded in place. I know that Albert does a complete header for my bike, but that features bigger bore header pipes. That would factor in another element to the design and would not confirm my suspicions about the standard collector. I want to preserve low end stomp over top end power anyway.

My contention is that if the Y shaped tin that the two standard header pipes are welded into was better contoured with a seamless join to the incoming pipes that a whole better responding XB9 can be had.
Ironically my spare header looks better inside the internal plumbing of my original header. The step from the incoming twin pipes where they are welded into the collector looks more flush. So there could have been some minor inconsistency in production? Now l am in a quandary about whether or not to cut up the better header or just fit it?

Having another good look inside today, l can see that the factory that made the pipes did stamp or press the sides of the Y collector inwards to form a slightly pinched contour that mirrors the twin entry pipes. However this ‘pinch’ point does not look consistent in shape as it goes in, out, in, then out again to flow into the single large pipe exit. Instead of going to the hassle of fabricating a new Y collector l can see a way of improving the shape of the existing metal. By applying heat and using a cold chisel, l think that the sides of the pinch point could be beaten inwards by 2 to 3 mm over a length of 30 or 40 mm to create a more pronounced ‘valley’ flowing towards the Siamesed pipe. This would reduced the volume of the collector and reduce the chance of gases ‘stalling’ or slowing at this point.

If successful l could then run this tweaked header with and without my Venturi to see how effective the pinched collector is. Shame about the lockdown, but then it could be a while before l get around to actually swapping pipes on my bike. More measuring to do first with my micrometer!

Sorry about some of the spelling and misformed words. That’s not what l typed. This damn iPad!

Has anybody tried a separate tuned exhaust pipe for each cylinder?

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Buell Ulysses XB12X 06/08

I did quite a bit of reading on this. In a previous link to RB Racing-rsr l recall them establishing that a well designed 2 into 1 was superior to twin pipes. They also discovered that the standard HD headers were actually quite good. It was the punters fallibility for fashion to fit poorly designed but loud twin big bore shorty pipes that robbed much of the power.

It has also been observed that in Germany the fashion was to fit high quality quieter 2 into 1s to their big Harley’s which make good power over a wide range.

In another publication on tuning the Evo X sportster motor one tuning expert observed that 80 % of early Buell performance was down to exhaust (whilst observing respectable noise levels). The next 10 +% from modified crank balance factor and the rest down to heads, pistons, fuelling etc.

Whatever the truth, l will be sticking close to the standard set up due to financial constraints!

I’ve been doing a bit of measuring on my spare XB9 header to get an idea of what’s going on.

The two header pipes appear to have a internal diameter of around 35mm. This gives a total cross sectional area of almost exactly 22cm2. They are welded into a Y shaped collector at which point the cross section suddenly expands to 23.4cm2. 25mm further downstream the cross section has increased to 26.5cm2! A further 27mm downstream and the section reduces to 20cm2. Over the next 40mm length the collector reduces to 14.7cm where the pipe becomes a single pipe of about 46.5mm internal diameter. So the Y collector basically converges two 35mm pipes into one of 46mm, but in a fairly haphazard way unless this expansion and contraction was designed in in tests of the reflected exhausts reflected pulse wave? I doubt this though!

Having said all that l could be barking up the wrong tree anyway. Looking at the header pipe entries there are already odd looking steps, probably because the 9 and 12 models use the same heads?
In which case the exhaust port does not see a seamless flow from the heads into the header pipe like something like a BSA Goldie anyway. The pipe flange is 41mm inside stepping out to 42ish mm over the next 16mm before a steep ramp down to the 35mm XB9 internal pipe size! I wonder what effect it would have if l made two tapered stainless snap rings about 15mm wide that clip into the recess or probably better to tack weld them in place, to smooth the flow from the heads to the pipes? Obviously one wouldn’t want such additions to come loose!

I will concentrate on the collector for now though to see what l can achieve easily.

Cylinder Head port size ,shape, and exhaust headers , size, shape and tuned length , It is a compromise between getting the timing right for the reflex negative pressure wave and anti-reversion methods to stop contamination of fresh intake charge .
https://www.v8forum.co.uk/forum/viewtopic.php?t=2931

https://www.researchgate.net/publicatio ... _SI_Engine

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Buell Ulysses XB12X 06/08

Thanks for those Barney. I love reading about American V8s even though l’ll probably never own one. I drove a few in Canada years ago and loved every minute (Camero RS, Pontiac Parisiene, Plymouth Fury...only small blocks, but....).

The second link is probably more relevant, particularly the paragraph on header sizes. I guess many will see my observations as trivial given that the basic dimensions of the 9 header are correct, but in detail it looks more of a makers compromise in being made to fit rather than to win any races. I suspect that this happened when the 1200 motor was re-introduced into the XB range. Later 9’s were also fitted with 1200 mufflers just without the servo to connect them. l’ve not ridden a post 08 model so l couldn’t comment. It’s a shame that demonstrating my experiments has always been thwarted by my inability to post pictures. But reading the link (of which l will do more) ......yes that’s what l meant!

I have enough power and torque for my needs. Given the torque reactions l am getting, l just need to smooth or flatten things out a bit. My Venturi and the apparent sensitivity of the exhaust system to changes where the header meets the muffler seems to indicate that is where the key to flexibility lies.
As l have said before, that may be why Yamaha fitted their EXUP valve at that point once upon a time.

One positive with this lockdown is that l now have more time to think if not to ride my Buell. I drew up my own design for a power valve, but that’s being filed for another day. l will just make incremental changes to my own system for now.

Love the V8’s got a351 cleveland in an old Italian classic I must get going again one day
Glad too of helped , many years ago when racing bikes , I did think about an inlet bell mouth that was adjustable in length , one tube inside another , and linked to throttle , in these modern times a little servo motor driven by engine rpm could be more precise on the correct tuned length . Same but different didn’t Honda have variable valve timing on some cars, were do you stop, the world is your oyster as they say, its only limitation your imagination or finances. One thing at a time, prove it works then carry on with the next phase

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Buell Ulysses XB12X 06/08

Yes you must get that 351 going sometime soon. The beauty of those old V8s was/is that they were mildly tuned straight from the factory and that you could almost double the power depending on how much you were willing to spend. I wish l could drive a big block V8 sometime. They say that the torque from a 426 or 427 is shattering!

Yes l think that a variable inlet track has been tried, but not sure if or who actually put it into effect.

Just to blow my own trumpet a little. I did sketch out an idea for a five valve engine with offset inlet valve angles and cam just like the FZ750 in a college note book in 1981 or 82 just before Yamaha introduced their ‘genesis’ range of fours in the UK. I should have patented the idea here and l might have been quids in! Maybe l should patent my power valve design before someone like Honda does it!? I don’t expect any prizes for tweaking my Buell as these threads only really apply to 9 owners and there seem to be few of us left.

Probably all broke their rear pistons and sitting at the bottom of the river Tame in Dunkinsfield.