what are we doing this year and what are our targets

Derek ,
Exhaust pipe lengths are now universally determined as percentages of the tuned length from piston face to rear cone / tailpipe junction !
So if you have books that were published last century and quote pipe details , ignore them , the exception to this would be Blair`s books , but even with these , recent developments dated them somewhat .
The list below illustrates the trend: All headers are from piston face to start of diffuser and expressed as a percentage of tuned length ---- t/l

Luyten Honda circa 2000 . 801mm . t/l--header length 32.33%
Aprilia circa 2006. 803mm. t/l--header length 32.2%
Honda CR Kart pipe circa 2009. 835mm. t/l--header length 31%
50cc 20bhp engine. 759mm. t/l --header length 32%
Mallossi 50cc . 714mm. t/l--header length 34%

A working summary would place header length at 30 to 35 %
The same factoring of proportions place diffuser lengths between 62 and 68 %

It would seem that these numbers offer the best compromise for a ball park working arrangement , but individual situations may demand something different . The big problem to predicting Bantam systems is that every engine varies in so many ways , and so would their pipes !

The consequences of too long a header can be seen at the ex port , with the delay in the beginning of the depression in the cylinder coming too late in the cycle when the revs hit the power range . What we should aim for is the widest and longest negative pressure ratio we can achieve around the BDC area when the transfers are fully active and lots of lovely fresh , pure and cool mixture is available , the reverse is also true of one too short !
So once your tuned length has been calculated , on the basis of exhaust port duration , rpm and anticipated average pipe temperature ( hence acoustic wave velocity ), the other dimensions can fall into place

As to whether disc engines differ to reed , or indeed piston port jobs, in their front pipe length demands , the answer is in the numbers above .

Hope this helps you a little , the rest will have to wait until tomorrow, as my calculator has just over heated and is smouldering from all it`s exertions !

Regards , Trevor

[quote="Derek"]

Trevor Amos wrote:

So my final question is "do you think" the top edge of the exhaust port is that critical to a Bantam Racer, and if it has such an effect on power band width/torque should we not have some guides as to a good width for torque and one for a higher revving "light switch power band motor", ?
(weather it be 125 or 175(190).

Hi Trevor thank you for that masterful explanation, I do hope your calculator recovers as i have so many other questions i want to ask.!
But from me should have said /asked about the exhaust port edge as the port opens ? - profile/finishing condition on the edge!.
So when your calculator has recovered, could it give me an answer, to my final un numbered question above (with a little detail or perhaps a sketch) , in the mold of that beautiful explanation of the % front /defuser pipes,
when my head has cooled down, I'm sure i will be able to understand it all a little better, now where's the Anadin, !!!!
Jesus said - giving "is to recieve" - and mathew vrs 23 chapt 5, thou chall recieve in plentyful when they give unconditionally!.
kind regards "Derek -
p.s im considering changing my avatar name to "the socerers apprentice"

Hi Trevor
interesting advice this one.

Trevor Amos wrote:

Derek ,
If no improvement is felt you can dispense with it , however , don`t expect a 5 bhp power jump , cos it won`t happen !

Trevor

you are right i does not give 5hp, will PM you the results!
.
Derek

What Rossi is doing this season now he is back on a Yamaha is the question. What a GP race? Second -- starting from 7th on the grid.

Remember we were trying to analyse why he couldn´t get the Ducati to work for him. Big and little flywheels and all that jazz...

So what was the reason for Rossi going so well on the Yamaha yesterday?

Towards the end of the race he was putting in the fastest laps whilst whittling away at Lorenzo´s lead. Should be some close racing again this season.


Cheers!

Derek ,
Having a very rapidly opening , square edge to the top of the exhaust port does create an intense and increased wave intensity , leading to a greater cylinder depression , over a more general , gradual opening style .
This effect was investigated by Kadenacy , back in the 30s , and this concept became known as the " Kadenacy Effect " , it is little thought about today on 2t engines but the F1 boys have embraced the idea for exhaust augmentation . As you say , the real downside is ring vulnerability , coupled with ever widening ports !
Bulk flow potential at high rpm , and therefore , limited blowdown potential , now demand a radius on the top edge blending to a downward sloping duct , so Kadenacy goes out of the window . Although it may be of little import , a sharp opening port will seem a lot harsher to the ear than a sloping one .
Bridged ports can safely have a flatter top , but a bridge incurs flow losses and will only , at best , be around 90% of it`s mathematical potential , and the crucial initial opening has 4 radii , and the bridge , for the gas to negotiate and which create turbulence , and we all know turbulence is a strict no , no !
A large , free flowing exhaust port has one huge downfall , short circuiting charge loss , from the transfers , to the exhaust port that plays no part in combustion , and this is one contributory factor to light switch power delivery .
At lower rpm this is largely overcome with the use of a 6 speed gear box and exhaust power valve , neither of which are available to a Bantam , so compromise between the ideal and the realistic has to be made ! For all it`s sophistication the Aprilia needs to have it`s power valve still fully lowered even at 10,000rpm and not fully open until 12,000rpm , so the massive free flowing export port only fully does that for a meagre 1200rpm !
Light switch power bands can usually be accounted for in a miss match of porting and pipe , with the whole lot only becoming synergistic over a narrow rev range , a common error being limited transfer bulk flow and long exhaust timing . It could be suggested that , transfer area and flow = power , and , ex timing = revs , get those two out of sync and 3 speeds become problematic , and , complicate things with an inappropriate pipe design and life gets very tricky , and also assumes that all is correct in the remaining spec !

So , what you could try is a lowish port height and achieve the timing by putting a 2 or 3 mm radius on the top edge of the port , flow at high rpm will be better , and if the duct volume is matched to the lower port area , and the correct header and diffuser pipe dimensions factored in , then it could work well ?


Regards Trevor

How are peoples performances going? compared to their targets so far this season?

I don't like to set targets as such, because it can be so off putting if you don't meet them.

Is there another Midland Meet in the next 5 weeks as I've a bit of free time and could come along..

Regards Mike

considering the hype, enthuasium, and what people have said they are doing/going to do the answere is not alot as from what i see by entering all meetings the grids have gone down this year where over the winter were going to have a full grid to ourselvels almost.

so what is the reason for all these bikes not been out??? is there things that can be done to help???

How ever it is good to see Mike Redhed back out and flying the flag as well as Graham Newman returning, and lets not forget Dan who had no exhaust barrel or head 5 weeks before lydden and sucessfully finished 4 pr6's and was going well.

I think its the cost of living at the moment ian everything has gone up in price  but wages haven't, and people are struggling every class and club seem to be down on numbers this year including modern racing simply because people cant afford cant afford it, i would be out on the track every meeting if i could but im having to put the extra hours in to earn extra money to cover the bills which leaves me less time to get the bike ready then to have to lay out avgas, diesel and entry fees i cant do it but four years ago i could

lets hope this recession gets out the way sooner  

I disagree with the cost issue, we are coming out of recession "be it very slowly", the problems or should I say answers to all your questions are all on here.

Perhaps if more people answered peoples questions then you would remove the enthusiasm /stigma of what is needed to compete in Bantam class, who wants to turn up at a meeting with a bike of at least equal power, or possibly even more, but get left behind, due to the handicap of his weight, most racers coming along and wishing to join in are heaver than the front 4/5 who are lightweights, weight on a Bantam makes a huge difference, Now that I'm involved in other areas of racing, it is even more aparrent of how important "weights is".

Summing up who wants to spend two years in the shed restoring /building, spending a small fortune on all that is required, Then watch the front 3/4 slowly pull away, "why" is the answer to your questions, why is because your formula is not as fair as it use to be. too many unfair advantages ! the 175 class was a step in the right direction, I'm not sure this is the  the correct opinion, but its an opinion, ! that possibly does not meet others, but low weight does have a significant effect, "try weighing all the bikes and riders full gear, after a race, before they are allowed to go back to the pits.

I'm sure you will see a picture, but as there are less / not many of you left !! your formula is simply in an unfair state" it needs looking at. My advice is "you need to look a little closer to home to figure out why your class is dying, and it is dying, the answers I'm sure are here somewhere, you just need to figure out why people come back try then give up, its certainly not costs, I'm sure its painful for some, to have to spend so much, then get nowhere. the list of people who have come and gone is endless is I'm sure huge, the same story.

I have to say I was extremely impressed with all the adds/marketing prints and leaflets that have been done, "well done" I actually came across some guy at Brands with one in his book.!!!

P.S
just adding the enjoyment point,- its very rewarding to start/build/develop /race, but its very frusutrating when its not enjoyable, perhaps an amalgamation with another club/class in similar situation, is a way forwards as it looks like it could soon become the only way forwards.

Derek

My goals were to ride out on track and back in again, managed that and learnt alot too, very pleased to only have a few gearbox issues to sort and some clutch plate to make,
I've thought about the dwindling grids a few times and frankly not sure theres a simple answer, the scooters are a good example, grids of 20 Plus, they have a good supply of off the shelf parts, they're not cheap but the grids full, say the word scooter to people in there twenties and they know what you mean say bsa bantam and you get " err what?"

Having the desire to give it a go is the key scooters aren't cheap and are full, Manx350's aren't cheap and there's loads of those too,of course if money has to stretch to cover everyday life the first thing to go is the hobby it's life and common sense,
I think what I'm trying to say is , you either love it or hate it,  so far that is lately I love it, but not to long ago the later!

Would weight matching make the grid swell? I doubt it, again other classes can give insights a quick look the likely front runners shows a mixed top flight of physical build especially in the scooters all sorts In there pack, maybe a good fat riders better than a trying thin rider.

I thought I'd put my pennies worth in on this. It can be costs and time that prevents people getting to and from circuits plus bike preparation but in my case it was finding someone who was prepared to do machining work for me.
I sent JS2 cases to be welded, 8 months and many phone calls I got them back ( a beautiful job and not too expensive) then came another year waiting for the machining to de done ( which never materialised) after collection I found someone who did the work in three weeks, now comes the barrel reline job.

I sent my barrel to a firm in Nottingham ( well known by all accounts) again another 8 months again many phone calls, on its return the bore was oval and it did not fit the cases but that's another story. I sent Mike Bridges barrel ( my first short stroke 1972ish) to the same firm and promised a quick return, 1 year and 2
months later along with the phone calls it came back ok. So it's not only cost that keep some away it's finding a reliable source to complete the work required in a sensible time.

 JS2 is ready and waiting for Brian to convalesce after his op and Mick's engine is near completion that should (hopefully) put 2 more Bantams on the grid.

Les 2012.

There you go three differing opinions, I'm biased I think you are all right, in my day it was all air cooled and iron wheels. and just 2 shiilings and six per meeting, petrol was only 16p pence per gallon, non of these litres rubbish,

but dcimalisation was a good way of charging us 5 x the amount and increasing it by 5 x the amount every time it goes up!!.

Really down to it there Terry!

Bantam Racing was, as Roy Bacon saw it -- "Racing On The Cheap". It WAS Low-Cost racing for a few years.

There were times when I thought we had so many members really wanting to race with BRC (we provided for the BITZA Specials as well as Bantams & Proddys & pukkha racers with the chance to race at reasonable cost ) we could up the entry fees and pay the marshals but I was shouted down. As I was with Fairings and all the goodies like ´WC etc... etc... ....

But now one has to look at the Bantam Racer with admiration. The modern racing Bantam is a fantastic piece of development, one we should all²²² be proud of... That is, although it must be a costly piece of ironmongery to be competitive....


²²² All of us who raced or worked in some way for the BRC -- so help us....

Cheers!

´

Hi JB I had a chat with the Boyler at Lydden and may be out on
his GP5 by the end of the year? That will be different..


John are there any 'modern' Bantam racer's ? I think what you mean
Is circa 1990s spec bantams ? Mine is very much late70s/early 80s
spec as I think most are. The most modern and currently the fastest
is Ian's bike and thats piston ported!

Regards Mike

Les, Joe, Derek have you any answers to what you see as the problems?

I can guess Derek's answer to be a combined rider/bike weight of 30st
Minimum. But how are we going to fit 8st to many bikes?

Les have you 2 riders for the two bikes? Matt Mouldens looking for a ride.
Young Luke Plane isn't quite old enough yet but give it a year.

Derek you have a post entitled 'A return to bantam racing' have you now
given up on your return?

Regards Mike

Hi Mike!

Now how about that! I have already forgotten your question ...

Anyways up -- it was something to do with Lydden and The Boyler. I fell off his ABS 250 -- just when I´d got it handling really well , at Lydden.  Wonderful bloke came and visited me next day. I was all bruised and battered and wept when he arrived that I had smashed up his lovely ABS -- boo-hoo, I am so sorry to have smashed your 250 ABS Andy... and all that ... but I put away the crocodile tears when he swore that he was not concerned one little bit about the bike, he wanted to see if I was OK. It hurt like hell to struggle into the sitting position and ask, "You really going to rebuild it then,Andy?"  Of course, he told me, but will you ride --?

-- Of course, I did. Unfortunately greed & ambition for money and status got in the way and I ended up in Canada  but I did manage a few more 250 races that were memorable, particularly a dice with John Senior on his Greeves Silverstone...

Ah, yes! I remember now. `Modern Bantam Race Bikes´ -- Sort of pre 1970... I meant when water-cooling was allowed in (`68 ...?) and  when we (the committee)  allowed in streamlning...
Then `Transitorised Ignition´ had them throwing away contact-breaker-points and all that old-fashioned stuff. I did the cycle parts as you see here on Icarus-1 -- including cad-plated frame (by blue-collar lads at Leyland Motors, Lancashire). I spent WELL UNDER a hundred
quid on Icarus-1 which included 4 sets of close-ratio gears (gathered from BSA Dealers en-route to Leyland & return)  plus all the tyres in 5 seasons of LOW-COST racing.

We have already done a cost break down on here -- not so long back -- and opinions have it that skirts & nickers, ignition-sets and even water-cooling don´t cost all that much ...!!???  It does seem that modern racing is beset with other costs that weren´t so bad 45 years ago.

What helps, of course, is sharing. I couldn´t be positive every time -- I had entered -- that I´d be there on time -- but when I shared with Niffy or Wobbleyman the meeting costs were considerably reduced...  

Oh pooh! That `45 years ago´ remark makes me feel ancient....  I´ll finish by saying -- I have no complaints -- I did not put the time & effort into the Bantams that most Bantam racers do  (Icarus-2 was a disaster of rushed and bad workmanship...) and I have 6 pots for 6 seasons of BRC (one trophy was stolen in Canada) racing that I can look back on with those 5 pots and remember every instance of the printed mention... Except one -- which I spoke of on here, not long ago -- which was at Snetterton, and must be a mistake, or, was it the day I fell on my head in another race?

Cherers!

JayBee.

Good Evening all,

Only a opinion but I would be interested to know why recent builders aren't out ie Nigel(Nobby), Colin(coneman) and Mark Taylor. Maybe they can tell us what holds them up even if it is good or bad?

Would we have a hit if a bike was available on a base of pay the race fees and fix it if you break it?

Apologies if I have covered anything that has been brought up before.

Kind Regards


Eddie

I know what you mean Ed there are a lot of bantam interested folk 'watching'
but not 'doing' but I'm sure they all have their reasons. Fair play to your
Dad he is is the only Midland Centre rider to actually enter a meeting? How do
you explain people meeting up to talk about racing a bantam but haven't quite
managed it yet?? People need encouaging but I'm scratching my head a bit now
its as if you have someone saying no no dont actually race! Just talk about it?

There are some bikes for sale 002 , ex bennion/dunne 175, martin nashs rocket
So there are bikes out there..there are people out there but we need to work out
how to get them together and race??

Regards Mike

Morning, my reasons for not entering are purely financial, work last year saw a massive decline in income.this year started off well but is again spiraling downward. Sadly there are more important things to pay for, before i even consider entering a race.My bike engine is in bits as we speak after siezing it again, HO HO HO,  some weeks back at a wednesday mallory test afternoon. Seems an air leak has developed around the transfer port(hairline crack) which has renderd the barrel useless without a resleeve. I am trying to put together another  set up just to be able to get the thing rolling again. my last outing, before it siezed, was going really well best the bike has ever gone, plug chop revealed a good colour after first session but second session coming out of gerrards the bike locked up. so back to sqaure one.So  new crank cases with un touhed barrel base transfers , standard barrel with 5mm whipped off the top, 5mm spacer under barrel, bit of jiggery pokery to get the transfers down to piston top and couple of mill to raise the exhaust port a little more.Had hoped to get to mallory for the race but shools have closed and it seems work has picked up for the next six weeks and ive got to put the hours in  while its available, so this is not looking likely.

Hi,all

I agree with Mike we need to find a way to get people who want to race and are going to race ( like myself) out there. There may be bikes out there for sale around £2000 but that is a lot of money. I'm hoping to be ready for racing next year(Leather,boots, ACU licence...) even if the bike isn't ready. 

Best regards Luke

Pssst Luke! Get all the things needed ready to race -- if your bikes not ready (and you´ve already had enough practice on whatever...) enter anyway and turn up at the meeting, for sure someone from the old Eastern Centre will lend you a bike to race.

Well, it used to be like that and I am sure that these days there´d be someone ready to lend a bike.....

Hi John, Thanks will have to give it a go  
best regards Luke

I see you give your age as 15 Luke. Have you yet tried riding a motorcycle fast on a  proper race track? What experience have you had?

I ask these questions because I just  remembered that when I lent my Bantam for a track day, practice session at Brands Hatch to a 28yr old work-mate at Ford the outcome was quite negative.  He owned a BSA 650 twin and was very quick out on the streets but out there on the track is a lot different from riding on public roads or out on a grass field. In being in fast company out on the track and trying to get round as quick as he could -- and being passed all the time -- he totally lost all desire to progress it any further.

There are, of course, young-bloods of your age who are already stars  in National & International -- even GP racing -- and others who´ve had years of junior scrambles or grass-track racing and quickly adapt to tarmac but don´t go thinking it´ll come naturally to ride a bike fast  on the race track.

If you haven´t done the above or been for the following I suggest you get along to an open track day with one of the Bantam lads and see how things go. I know an Eastern Centre chappy -- whom I shall not name on here, for obvious reasons  -- would probably be helpful in that respect. I guess its a matter of your getting to know him -- or another Bantam racer -- and taking it from there... Probably Brands on a track day.

I´d had 11 years of scrambling, grass track & Speedway training before ever trying road-racing and surprised myself  -- also frightened myself -- with the difference of riding-road-fast to those others. I had not intended to race again after retiring from Grass... but having helped build a Bantam Racer and developed its performance  by a lot of practice at Brands I got the bug and found out how different riding a 125cc, 3-speed, 2-stroke is from  500,350  & 250 4-stroke engines is on the road...

And if you DO get out in a race and find you somewhere near LAST -- don´t be put-off by that either.

I wasn´t.

Cheers! & all the best,
John.

Hi John,

I have a 175 bantam trials me and Dad built.There was a field near where we live where Me and Dad ride, since we ride it in the morning the grass is damp it is quite challenging at times, but I always gave it the a hand full though. Be it my Bantam or pitbike and whatever the weather i will give it a hand full. I'm not bothered about falling off. I know racing will be completely different from riding off road which Me and Dad have talked about numberous times. I'm not bothered about winning as long as i'm having fun. Me and Dad try and get to as many meetings a season as possible and we always try to have a good chat to the bantam guys

Best regards Luke

Hi Luke! you and your Dad -- maybe take your Mum too -- should get to a BRC meeting or Track DAY  and rub shoulders with the Bantam Racing crowd...

...they just love talking about racing  and/or riding/racing a Bantam racer.  

During my  scrambles riding times -- I say "riding" because my 350 Royal Enfield was never competitive -- I bought a 125cc Bantam grass track bike (for a fiver!)  that was very quick but was obviously not meant for scrambling because it threw me off just about every time I took it out on the grass and hit a mole-hill sized bump ... I found out later its front forks had been modified and the travel then great enough for the front tyre to foul the bottom yoke hence locking the front wheel...  Later still when racing on grass with 500 & 250 I wish I´d kept the Bantam because it was very quick and with another bike a competitor could fill in the boring gaps of not much to do.... There were in those days of 4 solo classes: 500, 350, 250 and 125 ....  

"Practice makes perfect" as the saying goes and if you have your parents backing get to a Track Day for practice on whatever you can get hold of, beg, borrow or whatever:  Snetterton must be your nearest road race track and whilst I hate That circuit for its nasty-moment memories I say go for it... Cannot be far from your place -- can it?

All the best -- and get cracking on the conversion Trials to RoadRacing Bantam...

Cheers!

JayBee.