Time,timing,time area ?

make that one more Trevor, I have certainly gained a great deal from your contributions, both on and off this Forum, and at the midlands meetings, I certainly know My bike is more powerful, produces more torque, and I better understand, what was always missing, anyway I have some really nice photo's for you to look at and enjoy, hopefully Ed will be along and post them soon, or please look on my face book page, as they are already loaded on there.

see if you can spot/name the Bantam racers from years gone by, could you believe there were more than Five former Bantam racers in the paddock at Silverstone BSB.

best regards Derek

Courtesy & Property Of Trevor Amos.

Trevor Amos wrote:

, power range  and notice I said range and not band, a different concept ?

More suitable power can always be found with a calculator, when all else fails !

Catch you all later ,     Trevor
 

hi Trevor

Could you explain more about this point range and Band !  please, as always believed they were one or the same thing !.


also how about a timing and area calculation based on a current engine, so we can actually understand/see what you are explaining.


rgds Derek

Nigel,
The pics are , quite obviously, various trans. duct mouldings taken using Vinamold, the small one is the RS125 cylinder , the others are various TZ125 arrangements . This is the sort of thing that high performance passages should look like , the triple Yam setup is perhaps a complication too far however , but make interesting viewing . The photo`s are still in the camera, but will get them up when I can, same with you Derek, been one of those days but I will get there !

Cheers Trevor

Courtesy & Property Of Trevor Amos.

Thank you Ed,

The first picture is of a barrel from the Honda 500cc GP engine, with the head still in place, and the power valve mechanism can just be made out, what is surprising is how similar the standard, over the counter porting, is to the works one. For anyone interested , the diameter across the cylinder base/ transfer duct interface on the std. barrel is 103mm, so using the bore dia. of 54mm a reasonable job of scaling the picture could be achieved to determine the other pertinent dimensions . Viewing these images, together with the Vinamold shapes will provide for an overall impression of good practice . Making a reasonable job of replicating one of more of these ports/ducts in the Bantam barrel can`t be too bad an idea , for you know they will be efficient !

Cheers, Trevor

Evening Trevor, look what i found under the staircase....

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sorry the bantam cast is a bit dirty.
so Trevor,
it looks like the outer wall and roof angle of the bantam transfer port could possibly be adjusted to follow that of the rotax barrel,the inner profile with the addition of may be some kind of epoxy resin could again be adjusted to follow that of the rotax barrel. The thing is that the inner profile would may be make the transfer port area smaller and that seems difficult to accept that this would be an improvement as you would think that the bigger the better.But obviously this is not the case as the new barrel profiles show. I can see from your barrel pictures that the large radius on the bottom of the barrels on the entry into the transfer tunnels of the modern barrels would probably take up alot of the bantam transfer tunnel entry if you tried to adjust to suit.... So im assuming that in standard form the bantam transfer port flow must be pretty inefficient in comparison to the point that by even making them smaller but flowing better is whats required.

Looks like I wasn't too far off the mark

Glad you persevered Nigel ,
Crikey that Bantam impression reveals just how poor the standard duct really is, when compared to the Rotax , ok for trundling to work on a commuter D7 and 6500rpm but not a lot of good when asking for decent power at 10,000rpm . Interestingly, the B port in the Aprilia barrel has a inlet/outlet ration of less than 1:1, which suggests that unhindered flow is far more important than just area alone, and the correct profile promotes and maximises the best flow . It is pretty easy to keep a race engine with six speeds constantly in the best power range but doing the same with only three needs a different approach and good power at lower rpm becomes crucial . Big ducts with slow flow rates at low down revs, that contain a large mass of inert mixture prior to opening, become a handicap so perhaps you won`t be too disadvantaged by being restricted to the old iron barrel set up that will peak at around the 9000rpm rate . The Honda ducts are helping to produce over 40hp at 12500rpm, so the modest 20+ for a Bantam will not need that geometry to get the best from it .

As you say Dan, not too far out, but looking at you inserts it might appear that the outlet c.s.a is greater than that of the inlet, which is not so good , but perhaps this is just an impression created by camera perspective at obscure angles ?

Catch you all later, Trevor

your right trevor , i should have added that the photos are of a scrap one that i made to see if i could make it! then i changed the sizes etc on the real inserts, i dont think i took a picture of the finished job.

Evening one and all, are the Jennings port time area requirements /calculating formulas still valid? Or is there more modern formulas to be used?

Evening one and all ,
                             Nigel , Jennings took his ideas on STAs, and a lot of other stuff, from the 1971 SAE paper published by Naito and Nomura of Yamaha, he distilled what they offered and came up with, in 1973, what has remained with us ever since . The trouble is he examined the available race engines and retro fitted stats. to suit his ideas , that was fine for then . Strategically , he ignored bowdown  t/a and concentrated on timings , to be fair trans. STA was pretty reasonable but has extended for todays analysis . A 2t race engine of today would not compete with one from then, if all of Jennings statements were followed .
Formulas for determining port areas and timings are simply maths and geometry so remain absolute and timeless . I`m not denigrating Jennings but it`s like comparing Concord with a Tiger Moth, both fly, but the comparable technology stops there, leave each to it`s own era .

The unique and specific needs of a Bantam , both 125 and 175, require very careful application and blending of all engine parameters to develop good performance . No point in taking the pipe from a RS125 and expecting 40hp, it won`t happen, but a formula could suggest other wise !

Cheers Trevor

As usual Trevor, so profound! That last sentence, I mean -- especially when reading some of the Elitist´s Papers..

Go well and keep well, with more power to your elbow....

Cheers!

JayBee

Courtesy & Property Of Trevor Amos.

Interesting graphs Trevor! 10% improvement on the 12 to 14 shape --´at 5500 rpm though... ?? and I make that a difference of 82.7lbs/in²(14) to 75.4lbs/in² bmep ...
 The difference in port shape definitely explains why we only had about 12horsepower at 8,400rpm  -- wind behind,  of course, and I wonder what we had in the way of torque because Icarus-1 was at times seeming competitive against W/C engines reputedly getting around 18horsepower at 10 - 11000rpm..  


  Was that QUB a flat-top piston?  or was it slightly domed as the Bantam?  

The racing QUB was a 250 wasn´t it?   And had the reed-valve which was Blair´s big innovation -- if I remembrer correctly.

Cheers!

It`s always useful to have hard data to explain and confirm the difference between good and bad, much easier to assimilate numbers than abstract theories . The same applies with context , the two ducts are from different Yamaha 250 single barrels that were rigorously tested at QUB, in this test the 8 barrels were the same in all respects apart from the transfer system . The odd numbers designating the two ducts , 12 and 14, indicate the various tests and not barrel number, there being only eight !
The BMEP graph really says all there is to know , the 12 duct is very reminiscent of the average Bantam shape, and it is no surprise that the 14 out performs it by some measure . The fuel consumption graph shows further inefficiency for number 12 duct. All of these numbers were collected at fairly modest rpm levels of 6,500 , if revs were increased , number 12 would worsen at an exponential rate when compared to the 14 duct . The course to take when modding your barrel is pretty obvious and any little deviation from 12 toward 14 is going to give an improvement !

Again, thanks are due to Ed for helping out with the post .

Cheers,  Trevor

John,
The 250 QUB twin had a half speed, cylindrical rotary inlet valve, driven by a toothed rubber belt, with fuel injection and gave around 62hp . Hepworth made the pistons that featured Dykes piston rings and a shallow dome to the crown! Their big 500 single, with piston inlet port, ended it`s development run with 72hp , and when you think the next best available British 500 single, the Seely/Matchless gave at best 58hp, that huge difference was quite incredible ! Just imagine that engine with water cooling, a reed valve and decent ignition, 80+ hp , no sweat !

Trevor

Thank you Trevor!
Interesting stuff!
It´s quite fascinating to think that whilst I was  sweating theoretical-&-mathematical-cogs at Bristol Uni learning  about Gas Turbines we had a visit from the Chairman of BAC, who gave  us a talk on, "The Coming Demise of the Reciprocating Piston Engine" -- (some such title as that) -- with the talk assuming and  concluding that the piston engine was finished and that trucks and cars would all be be powered  by gas turbines. Early sixties it was and about a decade later I actually witnessed trials of a  Leyland, experimental truck powered by a gas turbine. Even in early 1975 several  thought the gas turbine would oust the piston engine. I was working with diesels by then  and couldn´t believe what I was hearing -- and fearing...  

It was, of course, the gas-turbine´s  heavy  fuel consumption that killed it off for road vehicles...

I´ve not been able to get it out of my head though, that a constant speed*** gas turbine, as a hybrid prime-mover, driving a generator  and electric motor was never considered.

That´s now half a century -- plus a couple of years -- on from when Hooker (I think that was the Chairman´s name) stated the end of the reciprocating piston engine, so dramatically, was nigh --  and look at what we still have after all this time.

It´s magic -- that´s what!            


*** constantly running at its optimum fuel consumption....

Cheers!

As you say John , interesting stuff,
The Hooker you speak of was non other than Sir Stanley Hooker, who as a very young and brilliant mathematician at Rolls Royce, looked at the drawings of the Spitfire supercharger, did his calculations and much to his superiors astonishment provided evidence for an immediate 10% improvement in flow efficiency . He did this before even seeing the Merlin engine and had no engineering experience, he subsequently teamed up with Frank Whittle to develop the gas turbine and oversaw the RB211 creation , quite a pedigree . One prophetic statement coming from his autobiography " Not much of an Engineer ", and concerning the ill fated tie up with China and their embryonic aeronautic industry, and in a more general context, was that.... We neglect them at our peril ! How true that has proven to be .

Great memories for you John , wish I could have been there .

Cheers Trevor

Thanks Trevor!
Great days those.
I was an ADULT student and glad of having the opportunity to study full time. Even as an adult I believed everything & anything anyone with a title told me. We were all in awe of the man. That he could have been wrong proves the old adage that, "...he who never made a mistake never made anything..."

Speaking of China: when I was there (3 times) in the late eighties I found that many of their top-engineers never made anything -- just shuffled paper and made noises -- one of their younger engineers explained on the day before my last there, that it was because if anyone made a mistake in China he was never forgiven whereas if he made nothing --except for some noise -- he´d probably get promoted.

Somewhat like Ford Dunton R&D....

I don´t often wish for my time over again but I´d like to be at Bristol Uni just ambling away at Maths and playing with prime-mover theories -- just for the heck of it -- and preparing my Bantam with the knowledge gained on here.

Take care, go well and keep well,
Cheers!
JáyBee.

John ,
I`m not sure there are too many direct connections between the Merlin engine and our Bantams , but one line of development does indeed do just that. Taking his theories into reality the young Hooker calculated the if the diffuser in blower line was altered and a sheet copper intercooler was slotted in train, the mean inlet charge was reduced in temperature then power should increase. The end product of a subsequent drop of 25*c in the inlet charge produced a bonus of 30hp and took the altitude ceiling of the Spitfire to higher levels , giving an advantage over the German fighters.
So all you guys with hot air, flowing from radiators and radiating from ex. pipes pre-heating air going into carbs should take note , and, remedial action , for there are real gains to be made from a cooler, thereby denser and oxygen bearing, inlet charge !

Cheers for now, Trevor

Thanks Trevor! I hadn´t realised it was Hooker who´d done all those things on the Spitfire. At the Bristol Uni talk he never mentioned the Spit -- he was all go-go on the turbine.

Yes, I do know about keeping the air-charge as cool as possible and often wondered about super-cooling the transfer port channels. I think I mentioned it -- as a sort of challenge -- once before on here.

Cheers!

John-Boy!

Hi all ,
Whilst trying to steer clear of a physics and chemistry conversation, it`s perhaps helpful to state that engine power very sensitive to ambient air conditions and, conceptually, on the mass of oxygen ingested. This in turn should combine completely, in correct proportion, with fuel molecules to produce the ideal combustion burn ! Actually, it`s not the air, per se, but oxygen that we use, and with air standard values of 20*c , 14.7psi pressure, air contains 21% oxygen and we need to employ every trick available to cram that oxygen into the engine and use it to maximum effect .
Air density is proportional to the prevailing air pressure but, and this is the rub, is inversely proportional to temperature ! Typically, ambient pressure varies by around 3%, and temperature by 5%, prevailing humidity can vary dramatically during the day, even hour to hour, so these fluctuations are much more tricky to pin down ! Jetting changes can in the most part, cope with these variations, and so for our purposes air can be treated as an ideal gas.
Pre-heated air entering the engine is one of those down sides that can never be made up for during a later event in the engine cycle, and it`s consequences can be felt as far on as slower, less efficient combustion, hotter running temps and even contributing to detto .

Stated simply, heat up the inlet charge of air, from 20*c, and power progressively will drop off, but lots of cool, hence tightly packed, oxygen molecules flowing into the combustion chamber, seeking out a fuel molecule to mate with, will do their job very nicely thank you !

Stay cool ! Trevor

Exactly what I was saying, on here , yonks ago Trevor -- in a different way. The cold air with high humidity can be experienced as an increase of power when riding across Dartmoor at dead of night and compared with a hot dry day without the need of any scientific measurements.

All these modern tuners on here telling of their dyno test results so dramatically and NEVER quoting the Correction Factor Standard  (Norm, SAE  or DIN...)(for absolute ambient temperature, pressure & humidity)  they are using really makes my blood run cold. When I asked which Standard Correction Factor  was in use there were no replies. OK so its only a couple of BHP -- or kW -- with the Bantam but there´s a rule in engineering that we only compare engine dyno test results  when those statements of power are corrected to a Standard.

Ok! so I am being pedantic. If a Bantam engine produces 27 bhp then why not crow about it and forget the bullshine of Standards ...?

Like you were saying about Sir Stanley Hooker and his epic work on the Spitfire -- I´d reckon that 4% Correction on 400bhp as 16 bhp would have had him cringe if that amount went missing -- even when seeing  400bhp output.

What was the max horsepower of the Merlin in its last generation form?

Speaking of Oxygen:  it was a thought I had that if you had a flask of oxygen attached to the frame and a pipe attached to the transfer pots whereby -- with computer control, of course -- the ignition timing and fuel level  could be automatically changed as a continuous whiff of O2 was injected into the transfers just how much extra power would be possible?  Of course THAT would be cheating the Bantam formula but for the sake of science ....??  Or would the result be disastrous?

Silly questions I suppose....!?

Cheers!

John,
As far as I am able to ascertain, the type PV-12 Merlin of 1935 had a take off power of 740hp at 2700rpm, and the type 131 had take off power of 2,030hp at 3,000 , can`t seem to find the year, but then the Griffon was in use for the last couple of years of the war .
Just like the Bantam , steady development bringing to power ratings up and up?

Cheers, Trevor