Phenomena-Plus

Pipe 1 !

I'm gonna go with pipe 2

Hi Trevor

Now come on Mr Trevor, stop dangling the carrot - you have most peoples ear's "Im sure", use it the right way for the good of the cause, now what about those photo;s of that famouse engine strip? lol.

My request to you is as one of my pm "is indeed one of those filling your PM box" "but not for myself" I would request it be a kind gesture to post the reality.

I say the current pipe is 2 no "why" there is no doubt in my own mind - also you can hear it, on the video Mike Powell had at the classic bike show, from lydden last year I'm sure, its unmistakable the beautiful sound any 2 stroke on full song between 12,000.0 to 13,000.0 rpm!!.

so come Trevor gives us the figures, and stop playing, we are all enthusiats -besides I'm absolutly sure no one will laugh, they may doubt it" and 25plus ok!! but 30!!!!!!! yeh right? sorry just do'nt believe it, "I would need to see the readings on the dyno" my old honda in good condition started at 24 when we first bought, it was moved by dad to just about 28 and a lot of work. we lost the main barrel a blowup so put on a std item was only 22 but stilll really quick. after standing in the shed for 16 years it still gives just about 22 and is a lot faster than me bantam.

I think your dreaming at suggesting "30" but please feel free to prove me wrong in front of all!!! but please I want to see real dyno figures, I dont believe in the make believe world.

as for someone donating wheels I'm sure you can pick some up at an auto-jumble for a lot less than £500, besides you get out for nout in this world mate.

your last post was great by the way, full of helpfull and informative techincal stuff "we can all use", many thanks for your contributions the exhaust one for me has been the best "my favourite" its been very very helpful to me understanding the harmonics I always thout it was pressures not waves. no I now the wave harmonics create the pressure both good and bad. I never read this in a book I read it on the "BSA Formula Bantam Racing webb site".
!!

regards Derek Betts

Think of it as lumps-of-HIGHpressure-gas rushing in waves back along the steadilly flowing exhaust gas, Derek! I might be wrong but that is how I think of what is happening with a resonant exhaust system when in tune.

The animation (I mentioned) shows the whole mass of exhaust gas "bouncing" off of the nozzle walls and then that whole mass of exhaust gas rushing back to smash into the fresh dis-charge of burnt gas. Never! It happens as above...

What is fascinating in Trevor´s graphs is that the torque and power are still increasing as the lines reach 12,000rpm so I cannot get away from the desire to know how much farther the line extends? If as Mick says, 13,000rpm -- then the level of torque is then more than Pipe1 at 11.000rpm.

-- so Pipe2, although it might incurr a bit of unreliability would certainly make Bike+Rider accelerate quicker than when using Pipe1.... Top speed is essential but it is ACCELERATION taht wins races.

As I told earlier I got to Cadwell last September on the Sunday just in time to see Mark Carcreek go streaking away from the line -- thinking to myself, My Gawd! that bike´s got KERs (two enormous Flywheels running in vacuum chambers inside the `skirt´ that are wound up with energy in the Holding Area and connected up to the rear wheel at the start...) but I now know it was not a KERs² and that it was Pipe#2 ....

KERs²-- Kinetic Energy Recovery Systems á la Formula One ....

Courtesy and Property of Mike Powell



Numbers to the right are both bhp(power) and ftlbs(torque) Top lines power,
middle lines torque, bottom line air/fuel ratio.

Which power curve would you choose?

And what do you think was the 'Single' thing that was changed between the two runs?

Hi Mike,
Mainjet most likely.... I prefer the green line, at least on full chat you are safely rich. (Mixture that is not money!!)
Cheers
Alan

I have just done a re- run of pipe 2 having extended the rev limit to 13500 . The peak power line continues for another 500 rpm and puts on
about 2bhp , tricky to be precise as we are talking about the thickness of the printed lines . After that , power falls around 5 bhp in 500rpm and
then falls dramatically to the 13500 point shedding around 12 bhp or so .
Torque follows a simillar pattern but at 12500 falls of the edge . So at 12500 / 13000 rpm there are a lot of revs and no go , comparatively !
There are several points worth mentioning as well, one being the ign timing ,which at 12000 rpm has backed off to 5-6* btdc so almost all of the
combustion process will be conducted with a rapidly decending piston and enlarging cylinder volume . Pipe 1 at peak power rpm shows a much
higher peak cylinder pressure and temperature . And so , the merry go round continues , trying to juggle the good with the bad and come to a sensible
compromise . However , attempting to rev a Bantam engine regularly to 13000 rpm is perhaps not too wise a strategy to adopt , but , tempting
none the less for that ? More pipe work to come then i guess !

Power to you all , Trevor

Big advantage I see in Pipe1 is that if geared high and running at 12,000 rpm when coming to a hill -- or into a head wind -- the reduction of road speed and corresponding engine speed -- to say, 11,000 rpm means that from 12,000 to 11,000rpm there is a considerable torque back-up² to overcome the increase of Tractive Resistance, whereas a bike with Pipe2 would have a decreasing torque as more tractive-resistance slowed engine/bike speed.

Torque Back-Up² is a term used in Diesel Truck engineering.

Haven´t changed my mind -- I´d still like to have a go at revving the guts out of a Bantam that revs as high as the one with Pipe2....

Great thing about riding Andy Boyle´s 250 ABS was that it had plenty of torque and five gears which meant far less clutch slip and quite a lot more grunt and go....

What I have seen of Bantam perormance curves so far is that there is no torque back up -- as the engine speed drops so does the torque... Must commend you, Trevor if this is reality and not simulation....

Cheers!

On Mike graph - could be so many changes could make it richer -
smaller ordifferent combustion chamber / inlet trace length /smaller tail pipe / different exhaust / ignition timing / as Al said carburation,
so many things can affect this - but the main difference is "I bet the piston crown temp" is higher, where the fuel air ratio was a lower value/or is it higher ?

- trevor What a great little saying "may the force be with you" = (mass x accelleration per sec). and may the power be with you "too"

Derek

you just would not believe where Im posting from!

regards Derek

Two people have pm'ed ref power out puts of my dyno runs so in the interests of
being open and to incourage new starters etc they are :-

Blue Max Power 21.88bhp @ 10'710rpm Max Torque 10.98Ft/lbs @ 10'096rpm

Red Max Power 22.89bhp @ 11'746rpm Max Torque 10.76Ft/lbs @ 9'792rpm

Alan not Main Jet - Main jet change (i feel from past dyno runs) would put the
red line above the blue line not be under it to 10'850.

The carb, ignition and pipe were un-changed and Derek has got it (but which one?)

Piston crown temp - no idea can not measure it. (but running rich so cooler i guess)

I feel there are 5 bantam engines currently racing that develop more power than this one
and they are all at the front!!

torque is low Mike but great nice and open - no guessing to be done.

on the items I would guess at the inlet tract has been lengthened but only slightly, 10 to 20mm when the fuel air ratio is lower this is due to better timing of the inlet wave, creating a higher air /pressure and velocity ? basically more air, weekening the charge and al is correct it is richer on the other, I can not see colours at the moment, and yes Im just a guessing.

only reasons I say this is there is a dip or two in the torque figures if it was the head, from my own experience on a dyno, I think i would have expected the torque to be higher. but like I said I could have this wrong as I cannot see the graph colours, so !.

regards Derek

Courtesy & Property Of Trevor Amos

so trevor, what are the physical differences between the two pipes...

Hi All,
First things first , we all owe a debt of gratitude to Ed for posting up these and other peoples pictures and articles , and i feel it
reflects all that is good in the Bantam fraternity in showing mutual help and assistence !

I`ve separated out the two plots , the reason being that a composite squashes the line profiles and the visual impact is lost , a
picture speaks a thousand words !

Pipe 1 is the same as in the previous post , no changes , the alternative , in red , is an attempt to get somewhere closer to the
output of pipe 2 without the extreme revs . To be able to replicate the pipe 1 profile and gain at the top end came as a supprise,
the small losses low down can be ignored . With the torque figures dropping less dramatically as well , it`s a win ,win situation ,
with the beefier top end holding up the power and grunt .

The two pipes are both similar and yet very different , significantly , the tuned length from piston face to tailpipe entrance is the
same for both , as is the center section diameter . Header length , diffuser , center section and rear cone are all changed for length
and this of course means angle changes ! The rev increase from 11-11500 backs off the ign by about three degrees , and a bit of
fiddling here could improve things a touch more perhaps ?
As with all developement over an extended period , the devil is in the detail ,with patient, well reasoned adjustments being the
way to go !

I`ll be back ! Trevor

Hi Trevor

The graphs are very interesting and thanks to you and Ed for showing them.

Although you have folded the print-out over to hide the figures, you were good enough to label the torque axis as ft.lbs.

Making the reasonable assumption that the scale starts at zero and increments in steps of 1 ft.lb you have about 14.6ft.lbs of torque at 11000 rpm for pipe 1 and 14.3 ft.lbs at 11500 for pipe 2 which works out at 30.6hp and 31.3hp respectively.

The power graph is a bit more tricky to interpret - it cannot be bhp/kW but must be one or the other.

As a guess its hp with the axis starting at 10 and going up in steps of 2hp which would also indicate a peak of around 31hp.

Of course I could be wrong and I know its only a simulation but if its anywhere near right you do indeed have a 30hp motor.

Its a pity its so difficult to turn the cones on a drawing into a smooth curved metal pipe.

Do you have any thoughts or tips on that ? - perhaps in another thread if you or anybody else has a comment on that.

regards

Mick

well

where do I start

yes Eds going to be a legend "is'nt he" !! I look forwards to him joining in the fun and he so wishes to do so and needs the help and support like other including myself, and Im sure many others looking in.

On Micks comments - I see no one commented on my incrasternations, and i actually see that, "well "lots" being implied here, but what is actually being said, do we know! "I have no idea" - but I think I know ! and I think its prity poor show.

I agree with mick, her her' "well done to all those" for showing this type of open information, but to add "I feel in its current form it's completly and utterly usless, to those like myself and other to. !

So I think if we are going to wish to show information like this we need not show our webb site in this light, we should have some basic rules

"if you wish to help others by showing information "show it" -- please don't dangle carrots"

"help us, by showing it all" by hiding half the story!! or by missing out half the information - is very poor show for me.

Are we trying to creat a status que here ! sorry had to state this.

I feel and wish we could be a little more open, and not as protective/ or self inportant - of what we think we have, or for that matter "do"!

kind regards to all.

Derek

If Mick is right, about the nearly 15ftlbs of torque -- and if the torque curve is as flat as shown then this is surely a break through...

What is the Bantam first gear ratio: is it 10:1? or 14:1?? or somewhere between?

Including a rough estimation of the obvious transmission inefficiences that means roughly 135lbs (10:1) tractive effort at the tyre contact patch or 210lbs (14:1) ... whichever of the gears is used , which does mean the rider does not need to paddle with his feet to get a Bantam off the line -- as I have seen!

From pics shown of exhaust pipes on here I have asked about the very long two angle diffuser and the long diffuser starting from near the exhaust port and the longer, shallower angled nozle -- WITH NO REPLIES to my questions on these factors -- so now, from what Trevor says the Old Fashioned pipe with a `Belly´ (as the parallel portion used to be called) with Sharp angle diffuser and sharper angled Nozzle seems to be working better -- for Trevor! The Belly´s max dia is related to the Exhaust-Port´s cross-sectional area in some formula long forgotten as is the first bit of parallel pipe and the tailpipe lengths & diameters. So it is only a matter of getting them right to the formula by a bit of dyno development work.

Should be relatively easy to do on a dyno whereas out on the track the straight diffuser-to-belly-to-nozzle made life quite awkward....

I look forward to more comments with anticipation....

Cheers!

Wow our first 30bhp Bantam!! No wonder Trevor wasn't interested in Numbers!! He's got plenty!!

Ref 'Carrot Dangling' I'm very pleased Trevor posted what he was prepared too - as lots of people
looked in and some made comments and questions. Its all very interesting however none of it
helps any new starters. Where i feel pictures of an engine apart, tech data like- pipe dimensions,
carb size, ignition type and curve, compression ratio, bore x stroke, rod length, parts used ie honda
rs125 etc and so on... do help new bantamites.

Engines we have a fair insight into are Snowy's 175, Rob D's 125 and (a lot) on my 125
(plus Phil Betty's RV motor on the main web site).

The dyno readings i posted show what a small change can make? and yes Derek you were right
it was inlet tract length.

Thank you Trevor for your posts...

Regards Mike

Hi Mick ,
That was a fine piece of detective work , the actual numbers for the modified pipe 1 are

31.7bhp at 11500rpm , with max torque of 14.8ft/lbs at 11000 rpm .

And no , i don`t believe either , however , Steve was told by Tom that " we`ve got 26 but you`ve got a bit more " !
But does it matter very much , i don`t think so ?

Regards Trevor

Hi Mike "spot on" ref new bantamites.

Derek

Courtesy & Property Of Trevor Amos

Hi Ed , and all ,
Many thanks Ed , if the rest of the world was as efficient and obliging, as you consistently are, it would be a far better place !

Have a look at the latest offering and see what you deduce , as always the engine spec is of Mark`s Cadwell bike but with the
mod pipe , which only offers a little more right at the power peak point .
The reed trace , again , is squashed and the steep incline of opening rate is not really represented , also the left side pressure
ratio does`nt apply , however , the influence of the trace lines are correctly sequenced !

Must fly now , i`m next in line when John B has finished his half an hour of manipulative pleasure !

Trevor

Hi Trevor,

Your welcome, glad to be of help. I will wait for Derek to heckle me saying its because i dont do any work!


Regards



Eddie

thanks Trevore for pointing that out in my return to Bantam racing.

Now looking at this I may need a little help from you to be able to ready what is happening. I see in the area after transfer closing the wave/presure ratio jumps about almost as if the presssure increases then wall like its a flutting action. it this is what is distroying my packing on the inner walls of the transfer.

there is a lot here Trevor could you help us all the best way to read this please. I would really like to know why the transfers appear to be doing the same as the transfers ? and what part of the exhaust pipe has the most affecting on each cycle

but great information in there just need a little help understanding it I hope I' not the only one thinking this!!!.

Trevor please check you PM ! box

kind regards Derek