2nd order wave phenomena , and Dr Joe !

John , and all ,
You asked about reflections , primary , secondary and perhaps tertiary , however we won`t do the latter cos i can`t measure it !
Primary is defined as the various tuned lengths and any of the available exhaust software will get you in the ball park especially the one
suggested by Mick . Most of them are based on Blair`s and QUB work so you know it has an authoritative pedigree , but remember
software is empirical and only offers a starting point . What you end up with could be a fair bit different , or , you might hit the
" sweet spot " first go !
Secondary pressure waves are those that bounce around inside the pipe getting reflected by both the end cone and piston face .
The trick is to harness a returning wave and combine it , at a superposition location, this will augment , and broarden the subsequent
suction pulse around bdc ,and again, the following plugging pulse . This sequence continues at varying values within the effective power
and rpm bands
It is this phenomenon that can correctly be described as" Resonance " , hence the descriptive expression of exhaust systems for
two strokes .
I have asked Ed if he would be kind enough upload a print out , this will exlain graphically what goes on at a Bantam exhaust port ,
and is from Mark`s engine at the last Cadwell meeting . Once again picture and performance can be compared .

Catch you all later, Trevor

Courtesy & Property Of Trevor Amos

Thank you Trevor -- where did you make the measurement? I guess with a piezo-electric pressure transducer -- or is that Old Hat?

CheerS!!

trevor, whats the engine, 54 x 54 ? bore / stroke... conrod length?

Hi Nobby,
All the information you need is already on the Forum , dig around and have a good read !

Cheers for now , Trevor

p s , any one got any comments on the information revealed in the pressure trace print out ?
Got some interesting ones on the inlet/reed movement/transfer flow pressure responses .

Just finish reading a very good book of the life of Walter Kaaden, Walter wasnt very complimentary of Dr Joe. Walter's nickname for Dr J was 'the charlatan' based on the fact that he bought the early MZ secrets and passed them off as his own !! Good read all the same ...

OK....54 X 54/ 96 MM Diameter crank( made by yourself in somerset)108mm conrod?so the main exhaust port opens between 84-85 degrees around 28.1mm down fron the top of the barrel? A transfers open around 118 , 42.3 mm down from the top of the barrel?B transfers around 41.0mm exhaust duration around 189.9 degrees and transfers ( first to flow,last to open) around128 degrees? or should i start again ?

so..the graph shows the pressures of gases exiting the exhaust pipe?
is the little peak on the graph just before bdc the fuel being drawn out of the cylinder by the exhaust? how much pressure is in the transfer ports just before they are open and then as they open ? do you see an increase in pressure caused by the combusted gases being at a greater pressure for a period of time. which transfer ports flow first, mains or primaries . iwish i could send some pictures to post...just cant seem to get it right

Small wonder I had to do a lot of testing at Brands, mm-tribsa! --- with the Dr Joe formulated pipe!

Repeating what I´ve said before: The original `Dr Joe´ pipe testing at Brands was disappointing and I made a telescoping-parallel section coming from a sharp-angle diffuser going to the regular cone angle of the nozzle. Having got it work after making it short-long and in between -- many times*** -- to what seemed its optimum -- I made the real thing you see on the Avatar... Long stroke, CB ignited ... Icarus-1 revved to 8,400 full load but had a wide -- useable -- power band in excess of 3,200rpm....

Thing I have often wondered about is the lamina-flow bit where the drag of boundary layer causes a drag-difficulty with gas-flow which brings me to concern over the welding -- how all the little bumps (from welding outside) -- get INSIDE -- might, as rugosities cause some sort of disruption to flow... Hence the "practical" often coming out as quite unlike the `theory´....!?

*** I enjoyed practice, so much, at Brands that it didn´t matter about the time spent there -- particular when Café Cowboys on big road bikes could be beat-up by Icarus-1 Bantam, even as slow as it was, compared with short-stroke. water-cooled Bantams....

I don´t think "rugosities" is a real word but I like it -- it mean lumps & bumps from welding thin, sheet steel.

This topic is wonderful
Nobby i think Trevors exhaust will be 27mm and transfers 13.5mm Height, ?

not sure what these timings would be though.

kind regards Derek

Hi Nobby

Seems I could be wrong on the point about your point on the port timings on Trevor's engine, but now that I have a moments or two actually looking at the graph, I have to say I can see where you are getting the timings from, but I too could be wrong.

as I see/read the exhaust port opening is before the 90deg line on the graph (194 total) 96 or 97 approx.-

The transfer also before the 60 line so 65 / 66 deg (130) approx.

please correct me anyone, as this is important, i'm not sure who said this, but I too would like to see the pressure in the transfers just before they open on this engine too, as it would show "if" there is any reverse flow down the transfers ?. as I the exhaust has not pulled all the charge out still high at transfer opening, hard to imagine there is still lots potential for this engine even with its current performance ???

but boy would i like to know the set up and measure this, on my engine, as it would give such an advantage when tuning the exhaust inlet transfer phases with the pipe, and improvements with the pipe, no wonder this bike goes as it does,

Technology and knowhow.

what would we need to do this on our own engines, or should I say what equipment do you need to measure this, is it done statically or in motion, does it take a point of the crank or are these not in conjunction with each other.

If I was guessing it would need to be a synco-resolver linked in some way to a pressure transducer in the exhaust port, but the point of this would need to be very close to the exhaust port window for it to be done accurately !!, it would need to be a very sophisticated and accurate instrument to measure this in a cycle of about .000006 to .0000014 milli-seconds. can this be done when cam oval turning a profile on a large piston we could not run above 475 RPM as the sycno-resolver and sine wave actuator/transducer could not keep them both in sync ? if we went to fast. How this is done at 10,000 is amazing.

but it would certainly take out a great deal of the guess work and put you within a nat's hair of the "sweet spot instantly".

"guess work", this is for mere mortals.

kind regards Derek

Hi Trevor

Interesting the returning +ve wave is so high - have you any ideas as to what contributes to this large peak?

It looks as if that wave is returning a bit early even at 10,500 - what is it like at higher rpm?

Mick

Yes, in my opinion too it is high, Mick. Almost like supercharging at nearly 25psi but then I must admit to not knowing what Í am talking about because this is the first time I have seen such a curve and I never got into such development work except by Turbocharging. I did make a test rig when working at Walthamstow Tech to measure the phenomonen of "Water-Hammer" which is very similar gas-resonance, except with water you can see the pressure-head on a manometer!!

Wonderful!

`Scuse me while I muse a bit:- Not sure whether this is nature or science -- but, of course, it must be both: nature providing shock-waves at the speed of sound and science providing the measurement capability & equipment. Hmmmm??

Thanks to Eddie & Trevor...

Hi , all ,
I tend to agree , the numbers do seem high for a humble Bantam but this engine does go quite well and there has to be a reason for
doing so , maybe we are seeing it ! To put the Bantam in some sort of context , similar values for the RS and TZ are up around the
2.3 mark , both being arrived at by the same source . So a jump from around 1.8/1.9 to 2.3 , proportionally, is significant and puts
the Bantam firmly in it`s place .
Positioning of the plugging pulse at 10,500 could be better placed, but remember , this pipe was designed in 1997 for good results
with a static ignition timing and knowledge i had then , and has remained unchanged ever since . I guess the opposition may hope
that the revised pipe stays unused !
Software will always be optomistic , some greater than others , i don`t concearn myself with absolutes it is only changes that
interest me and that provide the lessons for future developement .
I would ask the question Mick , what are you comparing these numbers with and what would you expect to see as more realistic
values ?

Take care out there ! regards Trevor

Hi All ,
Actually, thinking about the printout and responces to it got me thinking . If by returning pulse , the exhaust pipe is being refered to, then yes
the value is lower, this being 1.55 at 10,500 and 1.6 at 11,000 ! The losses from the high initial number can be attributed to heat transfer
and friction and the overall pipe profile contracts, and in turn ,expands the pulse pressure leading to a reduction in efficiency . To say nothing
of the rubbish welding and dodgy construction ! By the time the pulse reaches the port it has dimminished a fair bit ,and this is shown in the
wave traces, to the illustrated numbers .

Hope that clarifies things a little ! Trevor

Hi all,
I have recently had a chat with an old friend who is a retired journalist , with a life long passion for all things bike racing. Topically ,the
subject of Dr. Joe came up ,and he recalled an incident involving the Yamaha Motor Company and the eponymous doctor !
On the basis of a stack of statistics , dyno results and manufactureing drawings , the good Doctor convinced Yamaha that the way to
future succes was to use his design for the rear offset squish band in their cylinder heads . Developement work done by him on the EMC
race engine was the basis for his claim that owners of this copyright had the holygrail within their grasp !
History has proven that Yamaha bought a real dog and Joe banked a nice cheque , suggesting that Joe`s abilities as a convincing salesman
were superior to those of being a design and development engineer !
I can`t independently verify this tale but i can vouch for the source and journalists have a curious ability to seek out the truth and to
expose the charlatan !
As a complete asside to the above , i read somewhere that one of the American race teams running the old TZs , with these heads fitted ,
found that during extended testing a tad more power was produce if the head was fitted the wrong way round ! And , that under certain
conditions the inlet flowed better in the reverse direction . Curious or what ?

Does make you think though , does`nt it ?

Take the day at an easy pace , that way you get to see another one ! Cheers , Trevor

so trevor , it looks as though the peak return pressure is strong but not quite in the right place, it looks as though you lose the benefit of such a strong pulse as it seems to fall as strongly as it arrives before the exhaust port closes. it would looks as though the full potential of the retuning wave would be better suited to arrive quite a lot later, keeping the pressure in the exhaust equal to that in the cylinder and not losing any charge.. yes or no? to achieve this what modification to the exhaust would be required as a first point , longer middle section or shorter or even less angle on the reverse cone? where was the sensor housed trevor,same place as shown on the aprilia rsa 125 fritzs pics. was this testing done with the bike static or whilst screaming round the track?or by simulation. what kind of sensor are you using pressure or heat sensor...doesnt pressurised gas increase its heat???

Yes Trevor! -- does make you think... And there was I, thinking Dr Joe was a clever old stick! Like I say I spent a lot of time circulating Brands getting the Dr Joe pipe to work and cannot for that reason -- of much fun at Brands -- really get down to blaming him.

No answers on his e-3 engine with its articulating conn-rod so I think that went belly-up as well.

Cheers!

PS-- Trevor!? I just read Nobby´s latest and have the answer but the question is addressed to you -- and regards the last bit about heated gas if you asked Derek he´d tell you it is Old Hat stuff! Derek´s gone quiet -- I hope he hasn´t been arrested for doing "Dead-engine, downhill coasting" in Public places??

...

Heavens above John , don`t wait to be invited , if you know the answer tell me , just tell me !!
I need to know , i have to know !!

T

well apparentlly.......

"The design and tuning of expansion chambers is a relatively easy process if you can define the criteria needed in this design. You must know the RPM range you want to operate in, the top rpm, the temperature and thus the speed at which the gasses travel (dependent upon fuel used and temperature inside the pipe)"

As the Aprillia engine seems to be flavour of the month it might be useful to point out that to get to the point of 125 class domination ,
on an international level , took years of continual re-design and developement , hundreds of dyno runs and way more than 200+ exhaust
systems . This number of pipes for one class added to the number that both Jan and Frits have designed for other marques , the total must
run into the thousand plus , might just suggest that pipe design is very far from as easy as banging in a few numbers into a formula !
Alan , for instance, admits to 14 and is still going , the sweet spot seeming to be as elusive as ever , as to me , well i`ve progressed up
to 2 on Marks engine . Being above all a pragmatic sort of chap i don`t fiddle for the sake of it , i do my homework and have mods in hand
to apply when the day arrives that Mark declares " It just ain`t quick enough now " ! Or , put another way , if your winning with what you`ve
got leave well alone and get on with enjoying the day .

By the way Nobby , have you formed any impressions or conclusions on the trace printouts i sent you ?

We`ll meet here again ? Regards Trevor

PS John , Dr Joe was a very clever man , no doubt about that , but did have a well concealed darker side , influenced by self agrandisement .
At least that is the informed opinion that was conveyed to me , sadly i never met him so i can`t say .
Gordon Blair , it seems, was percievd to be his personal Nemesis !

Hi Nobby -- well, if there was a straight thro´ pipe (with the timings and Blow-Down you use with a resonant pipe) the fresh charge would go from the port straight out thro´ into the exhaust, poof! There´d be no PLUGGING effect to push the bit of fresh charge back up it´s Jacksie!!

Instead, with a resonant exhaust pipe, the pressure wave reflection shoves the bit of fuel-air mixture (that would have been wasted) back in, Bopp!***

You could hear that `bopp´ sound at 3 or 4a.m. on any race meeting morning at Llandow when some local nut had to start his wretched hack ... There´d be, "...scuffle scuffle scuffe (feet on tarmac), then Bopp - burble burble... scuffle scuffle scuffle -- bopp. Silence -- except for muffled voices -- for ten seconds, then a repeat followed varrooomwowweee ... burble burble -- Bopp!"

That would go on for an hour or so -- the locals ensuring everyone in the Pits was wide awake -- then it would stop and I´d not be able to nod off again, waiting for the next scuffle scuffle bopp! I mean I needed my sleep after spending nearly a week in that other heathen county Lancashire, drinking beer with Leyland mechanics....

It got me into the bad-habits of going B&B with the Wobblyeman before meetings -- and when I say bad-habits -- they were!!

***Well, that´s `ow I fink it works. Trevor might have a more clear explanation.

Now, when considering how quick the Walsh and McPhee Bantams were which had megaphone and straight thro´ pipe respectively we (nosey Bs´ what cannot help being nosey about such things...) we have to ask WHY were they so quick? Well, the fact is they were both using VERY HIGH compression ratios and running on doped alcohol fuel and I feel pretty sure the McPhee had such a high compression ratio it ran like an aero-modellor´s motor in diesel mode.

With the Water Hammer experiment the effect of resonant-pressure-wave-charging can be clearly seen. There´s a long water pipe with pressure-guage before the shut-off valve. The water flows and the guage shows the Pressure Head of supply water. Shutting the valve suddenly causes a loud bang to be heard. The pressure shown on the guage increases in multiples of the Pressure Head -- DEPENDANT on how fast the valve is closed and how long the water pipe happens to be. In the case of water in the pipe (instead of fuel-air mixture) the pipe is stretched and its elasticity in return increases the reflecting-wave´s strength -- at the speed of sound whicvh cause the "Hammer"!!

Essentially it is the rapidity of shutting-off the valve that effects the increase of head pressure with water --

-- SO? does anybody know whether there is a similar effect with the 2-stroke -- ie Does the increase of engine speed (exhaust port closing faster) mean that the resonant exhaust pipe works better?

I think it does -- `Scuse me! Yyaawwwnnn!

" so trevor , it looks as though the peak return pressure is strong but not quite in the right place, it looks as though you lose the benefit of such a strong pulse as it seems to fall as strongly as it arrives before the exhaust port closes. it would looks as though the full potential of the retuning wave would be better suited to arrive quite a lot later, keeping the pressure in the exhaust equal to that in the cylinder and not losing any charge.. yes or no? to achieve this what modification to the exhaust would be required as a first point , longer middle section or shorter or even less angle on the reverse cone? where was the sensor housed trevor,same place as shown on the aprilia rsa 125 fritzs pics. was this testing done with the bike static or whilst screaming round the track?or by simulation. what kind of sensor are you using pressure or heat sensor...doesnt pressurised gas increase its heat??? "[quote] go on then john.. give me some answers

Hi Nobby,
You may well be correct in your analysis as to the location of the returning pulse ,however, as the peak is only about 18* or so
from port closure , to move it "quite a lot later " runs the risk of bouncing the wave off the piston face much more than is already
happening. This could be achieved by an alteration to the tuned length at the parallel section ,all other criteria will then remain constant.
Don`t lose sight of the fact that this image was offered as a simple insight to what can occure inside a Bantam engine ,something that
can be difficult to visualise , seeing the invisible if you like ! It is not meant to be definitive or absolute but just an opinion .
As i have previously mentioned the pipe was conceived in Aug 1997 , and, as i didn`t own a computer untill 99 it was draughted using only
scrap A4 paper, a pocket calculator and pencil .The convienience and speed of software came much later and also brought with it
infinite complication ! However , i am quite pleased with the pipe design as the bike went well with it and continues to do so .
There is one thing i have learned in that once the pipe is working , in the ball park , achieveing meaningfull improvements in a specific
area invariably means a trade off somewhere else .
The Aprilia sensor you refer to is a thermocouple , the prefered location was in the header but the vibration levels there destroyed the units
so it ended up in the compromise position of the cylinder ex duct .
All my work is now by simulation , initially , and on the track subsequently and if rider Mark says "thats great ,don`t alter it " then thats
the way it is , if he`s happy we are all happy !

Keep peaking you guys , Trevor

This graph shows what I was thinking earlier in the thread -

The red line is more like the ones Trevor showed with the initial peak lower than the reflected wave which arrives back at the exhaust port a little early, near transfer closing time.

The black line in this image is near to what I expected - the initial peak as the exhaust opens is higher than the reflected wave and the reflected wave arrives several degrees later.

They are both from a simulation of the same engine - the difference between them being only that the black line is with the rpm close to maximum power rpm and the red one is at 1200 rpm lower.

So if you get a line like the red one it could be a good one - dont alter the pipe - just rev it harder

Mick

[img][/img]

I am sure Nobby would as well -- I´d still like to know where and how these pressures are measured??

If we look at pressure above the piston then the exhaust port opening -- with the returning wave of exhaust gas pressure -- has that wave pressure rapidly blocking off the incoming charge from the transfers thus increasing the above-piston pressure yet not impeding the exhaust gas flow...

... this is whilst the piston descends and passes thro´ its stationary BDC. Thus as shown in the wave diagram the pressure above the piston has dropped -- by how much, I wonder?

Would it be as in the diagram shown?

Then as the piston travels upward the pressure above the piston increases even though the transfers are open -- because of the crankcase compression and the piston´s own displacement -- of course! -- and then before the exhaust port closes the returning exhaust pressure wave is present again and increases the (above the piston) pressure....

Sorry Mick! I don´t quite get the bit about revving it harder unless you mean that of being at the the beginning speed of pipe-efficiency and revving it up to its max speed in the effective speed band.

It looks like you´ve got <30° where the wave pressure is effective which would equate to how much in the effective rpm band? would it be 2000revs or more??


I feel like a dumb-dumb asking such questions but at the time I was trying to compete with Icarus-1 I left all this sort of thing to my engine man & race mentor -- I was hellish busy with loads of other things -- so I feel NOW as if reliving a bit of what I missed.

As I said before Icarus-1 Bantam had a fairly wide band of pulling-torque but with its long-stroke -- and other detriments -- was restricted to <8,500 max revs....