Dedication to a cause !

Here is a story to reflect upon as you don your wellies and wade out to the tuning shed in the back garden,
to try and find those elusive ponies. If you were here on the Somerset levels, that would have to be scuba gear!

To get power from the Aprilia RSA involved 5 day working with a dedicated team of 6 people, add to this the drawing office, electronics boffins and machine shop.

Work for Jan Thiel started in 1996 with 46.5 hp; and finished in 2007 with 54, so the average increase was .6-.7 hp; per year, doesn`t seem a lot really?
They made 350-400 cylinders per year, so that works out to 4800, add on the failures, and part finished ones etc, and that could have been up to 5000.
In all 30 different transfer port/duct concepts were tested, 20 exhaust ports /ducts, over 200 cylinder heads and 200 plus exhaust systems! Plus all sorts of ancillary stuff .
The work ethic was, have an idea, chew it around a bit have a word with Frits and try to get the modification implemented and tested before the great leader, ( Jan Vittenveen ) vetoed it !!

All of that makes my 50year involvement with Bantam engines appear, microscopically insignificant.

Stay dry, Trevor

Evening Trevor,  with regards to engine power. what did you start with? what have you got to date?  what was the single most change that produced the greatest improvement, with both aircooled and liquid cooled engine?  

Thank you Trevor, a very pertinent post.
To (hopefully, correctly) quote the great Winston Churchill, keep on buggering on. In other words NEVER give up. Half a step, half a step onward. If after a great amount of thought and calculation some modification is made and that modification results in a loss of power it is not the disaster it may seem to be. ALL information is relevant. Providing you document everything you do even a mistake is a step forward as it can stop you going up a blind alley. The two stroke engine has been refined and refined through many generations. The modem two stroke is a long way up the evolutionary tree compared to a Bantam. The humble Bantam has been going up it's own branch of the evolutionary tree for many a year, so like we as humans are 96% the same as Chimpanzees the Bantam is not the same as a modern two stroke. Therefore not everything that works with a modern engine will work for a Bantam, but most of it will with modifications to allow for the Bantams humble beginnings.
Keep on trying, the power is in there somewhere.

Mick.

Nigel,
it`s a little tricky to establish what the power output was way back in the mid 60s, dyno`s were few and far between, and expensive to use, so were out of reach. However, extrapolating from known speed and gearing etc, I would think 13hp would be realistic. Today, 25hp, depending on the pipe used , we have a pipe that gives higher output, but the one normally used gives less top end but far more mid range which converts to superior acceleration, which of course gets you round the circuit quicker.
Going back to the 60s, a 1hp increase on 13 represents a big improvement, about 8%, but that would be very tricky to achieve on 25hp.
Putting a short, 116mm, rod into a long stroke engine, together with more transfer area represented a big step forward. likewise, reducing the stroke to 54mm, again with the 116mm rod and more exhaust and transfer area , again gave a big improvement. All subsequent engines featured more transfer area with the greatest being now in the w/c engine, but I have to say that the biggest forward step came with making the liquid job. The reed valve enabled the use of a 5th,c, port and the reeds controlled all those nasty reverse flow tendencies, simplified carburation and enabled a big carb to be used without losing bottom end pick up. Reliable, predictable cooling brings confidence in using a suitable comp. ratio with out fear of deto, and so the gains go on. So, I suppose the biggest gain came from being able to eliminate all of the bad points associated with standard barrels on air cooled engines, and just as with the Aprilia, its all a progression, you think about it, design it, make it, and go racing, if it works, great, if not you think once again, and repeat the process, just as Mick has so eloquently outlined. But I have to say that the w/c is so under-stressed that several more hp must be available, if only the gear box could take it!
There are more basic things like a powerful, retarding ignition system that can make a big difference. I remember the first time we ran an engine with a Motoplat system, which replaced the contact breaker points, the difference was incredible, clearly the engine was held back by the poor sparking of the points system.
Re-making of the barrel, re-constructing all the porting ducts, and getting sensible ports in must be the biggest improvement, which can only be achieved, with water cooling, but is it a Bantam anymore ?

Regards, Trevor

Trevor, it seems to me that you have managed to coax quite alot more power from the bantam engine over the years, so much more than it was originally designed for . A great achievement.  Im sure the late b175 engine had around 10 ish hp when it first hit the road and i would hope my engine has slightly more than that after my humble efforts to improve it. It certainly felt the best it had ever been just before it packed up last time. Looks like Mallory park is to open again and the wednesday testing days are to resume, which has given me renewed interest and will give me the  opportunity to put my latest set up to the test... i have re-read the article on this site which Pete Tibbets wrote and i am looking to direct the air over the head and barrel more intensely  in an attempt to help with the over heating problem.( Using a water cooled fairing on an air cooled engine!!) i can see from looking at the engine from the front wheel perspective, that there are many things for a good air flow over the engine to work round before it gets there if indeed it ever does!!
   Ive noticed the primary chain doesn't take long to start flapping around either, some kind of direct drive would be good and less of a worry when gaining more power. I would have thought that after all these years improvement would have been found in this area, or has it?

Ive heard we may be in for a very hot summer, although i don't recall them forcasting all this rain!!. i hope the  Tory voters in Somerset  remember next year that Camerons government didn't give a monkeys about them untill it started to effect his banker mates in Surrey and surrounding area.........

Nigel,
Way back in 1970 BSA and QUB jointly developed the 175 engine with a view to making a half reasonable trials engine, and then later to a MX job. Running a 28mm carb and a 12.5-1 cr, 19.5 hp at 7500rpm was achieved, project forward 40 odd years of, potential, development and that engine would have easily topped 25+hp. In 1948, MV, got hold of the DKW RT125 drawings, just as BSA had, and they knocked up an engine that gave 10.5hp, so again, project to the mid 60s and 13hp is not that much of a gain, crucially, no one then, knew anything much about two stroke tuning. From the 60s to now, GP 125s can produce more power than a 500 Manx, so 25hp is not such a big deal, the technical information is there to interpret and use. It helps, of course, to have unlimited engineering facilities to make the bits, as I did. The biggest headache is applying all of this expertise within the severe limits that cast iron and 3 gears impose, then, analysing the inherent shortcomings of the original engine and correcting them, at least it sounds easy!

Great idea to get some ducting around the barrel and head, one thing that must be borne in mind is to ensure that all of the fore and aft air flow is gathered and forced to traverse the fins and there is no leakage from the top. Air will only flow if there is a pressure differential, and the pressure needs to lower at the rear of the engine than the front . F1 cars have quite small apertures in their side pods to direct air to large rads inside., this the interplay between velocity, expansion and pressure drop. And, be careful where the hot air exits, no pre-heating of the inlet charge, that reduces air density and robs the engine of hard won power and takes the thermal loading one step nearer to detonation!

All the best, Trevor

There is a common theme running through the brief illustration of some of the engines I have been involved with, but before we get to that, a little bit of historical progression will help.
When Yamaha introduced the TD1 series of bikes to the racing world, their two transfer ports were a mere 26% of cylinder circumference. The later TD2B had a 60% increase, with four ports, moving up to 46% of cylinder circumference.
The Aprilia ports finished up at 68%, whilst this was happening power continued to grow, culminating with 54hp in favour of the Aprilia. So it becomes, a not unreasonable conclusion to draw, that more trans. area helps makes more power.
Back referencing the w/c Bantam, the transfer ports in that engine occupy 56% of the cylinder circumference, clearly enough to attain 25hp, the best 175/190 I have seen comes out at 31%.

Trevor

"BSA Bantam Road Racer"

"After a very competitive 2010 British BSA Bantam Championship, it went to the wire with three riders in contention at the last race - Cadwell Park. Pete Tibbitts emerged victorious with his TorqSoft designed exhaust system. BSA Bantams only have three gears and thus the exhaust design had to give a wide power band. The result was 25hp at the rear wheel with the engine coming on the pipe at 7000 revs/min and producing usefull power to 11000 revs/min - using the original cast iron 125cc cylinder. "

would be nice to see some pictures as to what was going on inside Petes 125cc cast barrel.  

Well, there you go Nigel, if poor old Jan and Frits had known about TorqSoft, they could have saved themselves ten years and a couple of hundred pipes worth of hard work ! Fifty quid and paypal would have seen the Aprilia project sorted, no sweat !