Phenomena-Plus

Wow! Looking at those curves is like the times I am boarding an Airbus 380 -- I say to myself this thing can never fly!

The redline, the "Reed Action" is just as amazing!

NO! I am not criticising -- It is quite fascinating to me that so much has been done, of which I was unaware -- over the decades I have been adrift from Bantam Racing.

In the fraction of a second: 1/183rdsecond, the vacuum goes from around 1/2atmosphere to a complete vacuum -- for 110degrees of crank rotation -- back to 1/2 an atmosphere at full rotation!!

What are these reeds made of? that they can withstand such punishment? and how often are they renewed during a season`s racing?

The 1st Trans (Blue line) follows the Reed Block (black line) so very closely and gives that exciting blip of something like 5.3psi guage which from the baseline is 8.82lbs/in pressure boost or 23.5psi absolute ... which to me really does look like phenomena-plus!


What of the 2nd Transfer? or is that assumed identical?


Cheers!

Hi all ,
Derek asked for a few words of clarification as to what all of those lines mean , so here goes .
Before we get into that just imagine you are screaming down your favourite straight , on a lovely day and at your
favourite circuit where the revs have peaked out , and all is well in your world . This is where we are at with the print out ,
all the ducts are flowing with gas and forcing pressure pulses , on a cycle to cycle basis .

Perhaps the best place to start is bdc , the diffuser has lowered crank case pressure below atm ,and the inlet ,at atm aided by
a small ramming effect provides a large pressure differential which whacks the reeds open . Close examination of the traces
show that they all combine at atm and illustrates that the inlet duct length , for this rpm , is just about spot on .
At the peak of the reed opening an extra jab of pressure back up to atm just keeps the reeds open , after this pressure decays
the reeds start to close .
As the piston decends , increasing internal pressure ,transfer and crankcase pressures parallel each other untill the transfers open ,
the spike seen on the blue trace is flow reversal , initiated by remaining cylinder pressure , and delays flow for a few degrees of
crank rotation . This is the 1st transfer , and it follows that as it opens first but is delayed it will be the last to actually flow !
This helps to try and reduce short circuiting to the exhaust port , as it is adjacent to the exhaust port, and hopefully flow is underway
in the desired fashion when all ports flow ?
The reed trace comes quite close to symetrical opening but with a favourable early closing reducing blowback thus retaining valuable
charge to augment the next cycle .
Perhaps less obvious as a benefit of the extended open period that the reeds offer , is that the cylinder charge mix of fresh and spent
gas is slowly purified by fresh charge and at final trapping the combustable charge is purer and, therefore potentially, offers more power .
when combusted . At least i think that is what is happening ! ! ? ?

I`ll leave it at that for now, keep in touch Trevor

Thank you Trevor

very informative.

kind regards Derek

Courtesy & Property Of Trevor Amos.

Thankyou Ed ,
This picture illustrates what your up against when changing from first to second and accelerating hard !
Also why the need for engine and pipe parameters to be sychronised to achieve a realistic power spread .
There are other things shown here which come into play as well . Have a look , as they say , a picture
is worth a thousand words !

Catch you all later , Trevor

Hi Trevor!
Took a look -- Impressive!! What´s that in torque at 11,000rpm -- about 12.25? or is it at 12,000rpm?

Interesting bit is that the horsepower at 30mph is around 5... so taking that the power is zero at zero mph the average horsepower accelerating from standing start to 30mph is 2.5hp -- quite dismal! Something must be happening during that period of acceleration to overcome the tractive resistance ...??

The importance of gear-ratio closeness can be seen better if the Tractive Effort*** & the Tractive Resistance are both plotted on the y-axis against road speed on the x-axis.
Cheers!

***need the torque curve multiplied by the gear ratio for this... What are the three gear ratios ???

Hi Trovor

dont want to appear thick here but I do not know what Im looking at! so it would be really helpfull if you explained what I am looking at, i understand the graph is showing the bike changing from 1st to 2nd to top and Ican see it shows each time its going to 25.5 BHP and changing at eaxactly the same point, in each gear!

now my first question is 1) what are the red traces of or showing,
2) why is there a trace line at the lower end in top gear? not sure i quite undestand what id happening here, as you have said a picture tells 1000 I asume there are things here we should or need to know to help us while picking gearing and or ratio's to allow a bike to excellerate for the best options, at different circuits.


adding just spotted the drop between 2nd and top is a lot less than the drop between 1st and 2nd ??? I would like to hear what Mike has to say on this, any comments.!

regards Derek

Looking at Trevors graph - it looks like a 'dyno read out' so real? (or overlaid?)
Showing 25.5bhp at rear wheel which is roughly the same as 28.5bhp at the crank.
I assume the rev's are high so therefore the std c/r box hasn't got the ideal ratios:-
Hence the big gap between 1st and 2nd, Perhaps 25/22 o/p could be an option(availibility)?
Or lower the peak rev's to 9k so the gears are better spaced!? A backward step I feel...

hi Mike

Actually these gears are available Mike, I recently stripped a D7 or d10 and it had a set inside, and I had it for years and never new?

Actually seems most people just dont believe there are advantages with this setup, but I think we both know there are, Now when Ihad some made I had a few stes done on the basis i would sell them Ican not use them all so "I'm more than happy to share the gears, I had made, "for what they cost me", besides with the Tom and Brian mods, I really dont think the class has a problem with respect to Gears, well only if Brian or Tom says NO

cannot see that ever happening, so all you need to do is tell us the "big bang theory" on how to set these up properly, and thats sound like a snip-bit 9,000.


cheers Derek

Regards Derek

Why I suggested having a graph of Tractive effort²², on the y-axis, for each gear against road-speed, on the x-axis, is that you can see how close your gear ratios NEED to be ...

On Trevor´s graph the changes are at the power curve after it has drooped from peak power(onto the overrun ...) and this suggests to me that the Torque curve has a considerable droop also.

If the ratios are wide apart the torque curve should have a larger droop after (max torque speed) peaking so that as the higher gear is selected the torque is still at a high level of its curve...

I know that Bantam C/R top gear ratio can be varied from around 8:1 to 6:1 (by the 21 Gearbox-R/Wheel sprockets variations) but have no idea what the 1st & 2nd ratios are... otherwise I´d venture into the depths of this one.

But it´s Trevor´s Lot to get on with -- so!!!???

²²... Tractive Effort at the rear tyre contact patch is engine torque x gear-ratio (divided by the Rolling Radius) plotted against road speed -- it is the normal way for Auto engineers to calculate the in-between, gear-ratio steps ....

Hoping I am not butting-in too much here!!

Cheers!

PS -- I agree with Mike´s comment ... and I´ll say the power band has got to be wide to cope with that jump between 1st and 2nd gear... say about 5000rpm???? Phenomena indeed!!

And saying it again, I think a Tractive Effort versus Road Speed graph plot would show better this big gap between 1st and 2nd and how the wide power band with a droopy torque curve at its top end would manage to keep it competitive...

... otherwise at Cadwell the rider would surely be loosing on that squiggly, artificial Z bend followed by the hill...

Cheers!

Hi John

I certainly do not believe you are butting in john, all comment should be welcome as long as they are factual.

Derek

Thank you for the vote of confidence Derek!

Facts Derek!

Fact 1: With Icarus-1 our power band was just over 3,000rpm wide and a lot of people thought that was really good. Fact 2 was that it would not rev on beyond 8,400. So putting those two together we had power coming in at around 5,000 and that meant Fact 3 was a lot of clutch slip was necessary to be competitive.

Fact 4 is that what Trevor has is something amazing! A very wide power band, enormous torque and an engine that revs on with unbelievable peak power....

Fact 5 is that I am just learning what it is all about -- about 41-42 years too late!! I never found the time to look into any of these aspects closely because I was "always too busy" and left the engine to the `specialist´....

Fact 6 -- I thought fairings were ponsy and objected to their introduction into BRC on the basis of exploitation of "Racing On The Cheap".

Cheers!

Hi John

internal ratios for a full cose ratio set are

1.538
1.186
1.000

using the close set with snell output pair

1.675
1.291
1.000

Rolling radius about 11.4"

have fun
Mick

Thanks Mick!

So if Trevor doesn´t produce a Tractive Effort v Road Speed graph -- and I don´t fall-over in the meantime I shall play with the figures for a bit and maybe expose myself some more...

What´s the distance (radius) of the clutch inserts´ centre to the centre of the mainshaft?

Go well and keep well,

Cheers!

JayBee -- for John-Boy trying to grow-up!

John

I don't have a clutch nearby to measure but believe its 4" od so radius to centre of friction surface will be about 1 3/4"

Mick

Thanks Mick!

That was quick!

That´s about what I thought the ratio of torque multiplication had to be to enable a Bantam to pull way from standstill with any reasonable degree of acceleration.

I´ll try and show what I mean on a graph.... Looking at it from the horsepower view -- from Trevor´s graph*** particularly -- gives a dismal view of a Bantam struggling itself off the grid without clutch slip....

*** approx 6 horsepower at 30mph!!

Courtesy & Property Of Trevor Amos

Hello every one ,
Another installment in the ever expanding world of Bantam Racing !
The gearing graph is a small component of a raft of information provided by a , whole machine performance , piece
of software ! As any one who works with software will confirm the end result is only as good as the software its self
and the accuracy of the information fed into it !
The data needed to actually produce the outputs include rider weight, ditto machine , all gearing from crank to rear wheel
dia, machine frontal area , gear change speed , flywheel inertia , a fully plotted dyno read out and so on .
I posted the graph up to try and illustrate , as i initially suggested , to pictorially illustrate the need to take on board the
significance of tuning for an adequate power band with only 3 speeds and not just for top end power !
The red trace on the latest post is the one in" gearing " , it may not conform precisely but you have to allow for scale
and software vagaries . Incidentally . the caption should read 1997 not 87, sorry about that !
The other power traces show huge , low down, power gains with the ignition advance available to us from 2011 on .
As Derek has reported , correct transfer duct proportioning can offer significant performance gains , this i did for 2011
together with pipe mods and the result can be seen in the green trace
Should any one detect glaring errors with the gearing graph it could be down to my incompetence in loading the initial
data and/or working with , what is now , pretty obsolete software . I could go through the old data to re examine it , but ,
again it is the differences in progressive information that matters not the absolute number , providing that a possible error
in data input remains constant !

Have a look , see what you come up with ! Cheers for now Trevor

Ah! I was forgetting, Trevor! -- both you and Mick do not need a plotted graph (involving hours of calcs) from me because you can just call it up on your simulation programmes. So you could easilly plot Tractive Effort (in N or lbsforce) against road speed from your already published HP-Speed curves. I´d like to see it because it shows how as the gear changes go up to the next gear the torque curve gets longer and less curved and from this you can see how well mated the gears are to the torque curve shape realtive the actual road speed. The optimum is to have the UP gear change happening near max revs in the lower gear to mate with higher part of the torque curve in the next higher gear....

Sorry Trevor! I made an arithmetical error in reading your graph -- the one previous to this last one, I mean -- I said that the power band was 5,000 rpm when this latest graph shows 4,000rpm. I remember well other riders -- 1967 -- 1973 time complaining of only having 2,000rpm...!!

Last word (really??!!) -- "... 6 hp at 30mph..." , on your previous-previous graph (that I mentioned before) means 75 pounds-force at the rear wheel contact patch and we know in truth, reality on the road, it is much more PUSH than that.

Here´s hoping I am not being a pain....

Cheers!

Hello John ,
A Bantam treasure , being a pain , just could not happen ? !
Keep entertaining, observing and commenting i for one just love it !

regards Trevor

Hi Trevor! -- I could not resist it and translated your green power curve into torque against engine speed and that is some torque curve!! It was exactly as I was chewing on earlier -- the Torque-Back -Up is over 40% which is better than many turbocharged diesel-engined ...
The black line -- last year´s version was already a quite impressive (approx 11% or so...) and explains how Mark accelerated up the hill to Charleys last September. I actually managed to get there on the Sunday ....

Please excuse this as just a bit of brain exercise. That´s because I´d thought it might be falling off its gimbals any time soon -- I was halfway up the stairs and stopped for a breather and then couldn´t remember if I was going up or down ....!!

Cheers!

Obviously I was going up -- that´s why I stopped for a breather...!!

I looked again and think it is a 5,000rpm power band...???

Yaaaawwwnnn!

That graph "Power Through The Gears" by Trevor is haunting me.

The curve from 0 mph to 40mph is smooth until nearly at 38mph it has a bump in it -- what caused that?

And at 40mph (58.7ft/sec) the horsepower is about 7 (3,850ft.lbs/sec) so the push that causing this displacement is a mere 65.6lbs of force. If the rider plus bike weigh, say 340bs, this gives an acceleration of 6.2ft/sec² . Does not seem enough -- I would expect nearer twice that....



Cheers!

Interesting no-reply...

... CAD -- computer-aided-design -- and simulation programmes rely on accurate information being fed in to enable good information coming out.

If you are calculating power at the rear wheel it is necessary to know what the friction losses are in the engine and in the transmission with a fair degree of accuracy to be able to state the realistic power output of the engine. I also asked recently what the transmission efficiency should be for the modern racing motorcycle ... Again no answer. That was when I mentioned an example related to a motorcycle inertia, circa 1939 or so ... the professor had stated the transmission efficieciency as 88% which by anyone´s reckoning means a lot of power going to waste (heat?) thro´the gearbox and chains etc... etc...

Say 12% of 30horsepower is wasted in the transmission -- that´s 3.3 horspower or something like 2.5 kiloWatts of heat going somewhre?? -- WHERE?

Also! I guess these simulation programmes include Correction for ambient temperature and pressure -- to some Standard or other -- but they are never mentioned, so again, I look at the results with some scepticism. The argument against that, of course, is that in England the ambient temp... & press... doesn´t vary from tropical to arctic in short periods of time.

OK! OK! so I am just being awkward again.... I know you blokes have got bikes to prepare for next weekend so I´ll get LOST....

But it is nice to play with numbers when you have nothing else to do....

All the best -- and don´t forget the `force of g´ means that if you hit the deck with an acceleration equal to g the force of contact is equal to your body weight....

Cheers!