.................*NICK BRAMLEY'S 186CC ENGINE*.............

well the test was a bit disappointing with low figures, the motor was running well rich, a quick fiddle with the carb gave and extra 3.5hp, which sounds good until you see it started with 12 and a bit!

i have made progress with my aim of a broader powerband (starting a 7000 to 9500)but at the expense of peak power, my new exhaust port position is clearly not right, the first engine is peaky but this ones 9hp down

on the whole though i can at least take a few positives from it ,in as much as i know i made the ex port lower and expected it to knock the power so i know the route to go on,

i was hoping to use this engine as a straight swap if i have a problem and as such was hoping to use the same pipe, this i think is a bit optimistic on my part with my new port timings, so maybe a new exhaust before i go moving ports,on another plus it rev'd okay to 10000 with no leaks or other nasties going on,

Hi Dan,

Good Day!

It is tea break time so more forum attention!.....................

Great news that you have some data now from the dyno runs!

You are probably right with your conclusions!

https://2img.net/h/s6.postimg.cc/5f359p841/DYNO_RUNS_PIPE_4_3_17_SEPT_2014.jpg

Nick,Chalkie and I learnt a bit on this session!....................

Have a Good Day!

Rex

Just a small observation here, but one that is significant.

After scrutinising the respective dyno reports in this post, I compared the ambient air temperature that the two test sessions were conducted at, Rex at 79.63*f and Dan 49.3*f, knowing that air density is highly influenced by temperature: high is less dense than low temperature. Converting to *c and consulting standard air density charts, the respective numbers are, in kg/m-sq, 1.180 and 1.247.
Denser air has carries more oxygen molecules to combine with fuel molecules to make power. If Rex`s test was conducted at Dan`s air temp, his engine would have the potential to make more power.

Prevent hot air from entering the carb bell mouth, works every time, and it`s not often you can get something for nothing.

Always look at the small print, it`s surprising what you may discover lurking there?

Trevor

Hi Trevor and All,

Good Morning!

You are so right!

Often we only see the real gems in hours on the dyno when we study the information in the calm light of reality afterwards!

It is a most worthy cause!...................

Good luck with your preparations!

Rex

Good Morning All!

Time for a cup of tea and more computer learning!

https://2img.net/h/s6.postimg.cc/b1aqsi8gh/BANTAM_20_BHP_ENGINE_DATA_Page_1.jpg

https://2img.net/h/s6.postimg.cc/6tfyjr70x/BANTAM_20_BHP_ENGINE_DATA_Page_2.jpg

https://2img.net/h/s6.postimg.cc/w0quk0a4x/BANTAM_20_BHP_ENGINE_DATA_Page_3.jpg

https://2img.net/h/s6.postimg.cc/8nst1hu1d/BANTAM_20_BHP_ENGINE_DATA_Page_4.jpg

Looking forward to Mallory practice tomorrow!.............................

Rex

Thanks Rex,
Good info for all budding 175ers, modest tuning spec, running very efficiently and making the power, an object lesson for all aspiring tuners! Can`t ask for more than that, well done Rex!
Hope Mallory is a productive test session for you and Nick, and we get more feed back of the sort you have already revealed.

Trevor

Hi Trevor,

Thank you for your kind words and inspiration!

Now some more tea break information!

https://2img.net/h/s6.postimg.cc/3tyjcisi9/ANDY_BACON_RACE_PIPES_3_4.jpg

See you all @Mallory!......................

Rex

Thanks again Rex,
Interesting pipes, looking at the upper of the two, is the rear cone really longer than the diffuser, if that is the case it is the first time I have seen that on any race pipe? And why such a short diffuser, knowing this is responsible for doing the work in moving mixture from the case to the cylinder over the entire transfer duration? It all looks a little disproportioned, but you do get almost 21hp, so I`m confused!

Trevor

Hi Trevor,

Good to get your reply!

Inspired by Jan Thiels development of the works Aprilia, we chose to modify our 14HP @5400rpm trials/road cylinder into a quick road tune based on figures from a Ron Phillips (Fahron) motor.
Results were encouraging with 20HP achieved fairly quickly!
Nick approached us last Feb/March suggesting some actual race testing in about a month's time!
That sounded a Great opportunity so he built a new motor with the dyno top end and Andy Bacon made a new race pipe to suit!

Nick has agreed to fill in some technical details and preparation notes as soon as he has his new business venture (Bantam engine building and associated services like crank rebuilds) up and running!

Meanwhile.............More bike photos..............

https://2img.net/h/s6.postimg.cc/sh0ttbnip/NICKS_BIKE_MALLORY_PRACTISE_2014_6.jpg
https://2img.net/h/s6.postimg.cc/ekslhfr9t/NICKS_BIKE_MALLORY_PRACTISE_2014_5.jpg
https://2img.net/h/s6.postimg.cc/kqu1o6l75/NICKS_BIKE_MALLORY_PRACTISE_2014_4.jpg
https://2img.net/h/s6.postimg.cc/o961kkm35/NICKS_BIKE_MALLORY_PRACTISE_2014_1.jpg

All the Best!

Rex

Rex,
The Aprilia engines have established themselves as the exemplar from which all other engines are judged. Jan and his team achieved an unbelievable level of performance from an engine the same capacity of Bantams, sadly the comparison ends there. As is so often the case behind the name lies a team, and the responsibility for all of the gas and thermodynamic calculations went to Frits Overmars, a Dutch physicist and race enthusiast. So if you want numbers, go to him, it is he that published one of the works exhaust pipe drawings that has the basis for this post.

Using the published performance data I was able to calculate the speed of sound in that pipe as; 587mtrs/sec, and that gave the average pipe temperature as 590*c.
I did the same for your pipe and the stats were; 546mtrs/sec and 486*c temp.
Inserting the Bantam numbers from here on the Forum into the same formula gives a t/l of; 546x178x88/7750 = 1103.5mm.
Blair and Overmars suggest rear cone lengths as; .240 and .236 x t/l respectively.
1103.5x.24=265mm.
Modern thinking dictates that you have to work with percentages of the t/l, the normal length for header, including the port and duct, is 30-33%, and for diffuser 64-68% with a wider power band edging for the longer lengths. The longer diff. gives a better case depression around bdc and later in the cycle to boost mid- range scavenging.
A quick comparison with an Aprilia pipe drawing will show the proportions very well.
With any system compromises are made but there is always more that can be learned by anyone, and a closed mind sees less than a blind man!

Trevor

I'm wondering to what extent Aprilia's data can usefully be applied to a Bantam. If we are talking about recent Grand Prix engines, would they not have been operating at very much higher revs, using six gears, and watercooled? I don't have any answers (I have little understanding of the questions), but an engine working at - say - 9,000 revs, cooled by the passing air, and required to have a wide-ish power band, might be an altogether different proposition.

Perhaps MotoCross, or Kart, engines might be a more useful comparison.

You may well feel that to be the case John, but the Aprilia, the Bantam, a 1cc model aircraft engine a lawn mower and a Manx Norton all are governed by the same Laws of Physics. It is the application of those laws and interpreting their effect that makes the difference. Imagine the passage of the air/fuel mix in, through and out the engine and apply gas and thermodynamics calculations to that mix. Couple that to exemplary engineering that facilitates and maximises the potential of that mix and you have exemplar engines irrespective of their origins or the use they are put to.

Trevor

Morning Trevor and All,

Thank you for your kind reminder of Jan and Frit's methodical approach to the subject and your wise observations!

It is indeed encouraging and motivating that people like you care about the future of the two stroke! That does inspire us to go on!

We have a fair amount on the to- do- list and ideas with latest technology will be a great part of the program, like our fuel injection project (currently 19bhp @7500rpm)

We are most fortunate that our "Great Leader" is far keener than previous

ones!....

That alone might be the most essential ingredient necessary for the ongoing development!

Have a Great Easter and keep up the Good Work!

Rex

Where do you stuff the injector Rex?

Hi John,

Good Morning and a Very Happy Easter!

I would love to elaborate on this topic, but this is already a 10 year project with a partner manufacturer and you will understand we have a confidentiality agreement!

I can tell you they are very keen to develop low rpm, low power 2 strokes: also with total commitment!..............

Let's make today "Eggciting"............ .............Rex

Well done Rex! I just got stuffed in a pleasnt manner. I know about this sort of security lark because in Canada our [German)] company were into a fantastic combustion system -- Diesel unfortunately -- where the chamber was a unique shape in the piston crown and squish and swirl were also unique, the `tight´squish was new in those days and the Bosch injector very special. Lab experiments i.e. dyno testing showed a low peak combustion pressure and a wonderful Heat Relaese curve which showed the high pressure Work Done was AFTER TDC with consequent fantastic specific fuel consumption.

There was a Texaco Diesel sytem at that time with injector and spark plug -- Direct injection into the combustion chamber with adajacent spark plug and low compression ratio (compared with normal DI diesel of 21 plus,,,,) which almost equated our system.

With diesel, of course, at that time of all things mechanical, our rated speed was low -- 4000rpm -- and any sort of system now must have microprocessor control which I imagine is essential -- if i guess at what you might be up to....

We failed. I mean our Canadian(German) company failed. I said we would because Detroit was in depression and too many American senators (some ex-generlas of WW2 and even one of WW1...) knew our "AirDiesel" engine was not Canadian but really German and although our engine was the best performer it did not gain the Hummer contract which had our parent company in Cologne close us down.

So, if you are onto something good, hold it close to the chest because there are a lot of sneaky types out there ready to jump in and say they thought of it first....

Take care,

All the best,

JayBee.

Hi John,

Good Day!

Good to learn your notes on injection!

It is really helpful to learn what does work!

Debb's heart misfire appeared overnight, so considering the full schedule today here we offer a small, but important addition to Nick's engine spec!................

This is the hi-silicon content (22-24%) piston we use with a chrome-faced single ring! The skirt length is long so we can machine it to give different inlet timings! It is currently set at 147°.

https://2img.net/h/s6.postimg.cc/yqrjq4a1d/64_MM_SINGLE_RING_PISTON_TS185_BASED_Page_1.jpg

I am aiming to be at Mallory both days and if anyone needs midnight oil workshop facilities/spares, that would be available also!

Have a Fabulous Week!................. ...........Rex

Hi All,

Good Morning!

It's an early morning start here at HQ, enabling us to complete a few things as Debb recovers a bit more!...............

While Nick sorts out his new business venture I want to share our considered importance of two stroke carburation with the 20HP engine!

https://2img.net/h/s6.postimg.cc/79oekqpjl/BSA_BANTAM_186cc_20_BHP_RACE_BIKE_TONFA_Page_1.jpg

This sheet show Nick's carburation set in the first ever race event of the engine at Tonfanu last year!

Although he had a win in the first race, mid range pinking was evident!
The carburation was based on road jetting: I had road tested over 3 months in the winter and used 30 litres of AVGAS to determine the road setup!....  
The lesson revealed that race conditions demanded a somewhat different set up!

https://2img.net/h/s6.postimg.cc/x6i2xct75/BSA_BANTAM_186cc_20_BHP_RACE_BIKE_MALLO_Page_1.jpg

This next event at Mallory with slightly lower compression ratio and carburation similar to dyno jetting on needle and needle jet eliminated 98% of pinking and brought a fastest lap in one race to boot!
Small changes but very significant!....
(At no time was detonation evident as can be seen by previous piston crown photos!)

https://2img.net/h/s6.postimg.cc/6mphv7snl/BSA_BANTAM_186cc_20_BHP_RACE_BIKE_DARLE_Page_1.jpg

This last sheet shows the Darley Moor carb set up and we were pleased with the performance of what really was (by modern standards) a low power, low revving engine!...

Thanks must go to Nick for his confidence that the potential was in the engine and actually demonstrating it in the "real world"

Our exciting 2 Stroke journey continues!

Good Luck for Mallory............

Rex

Hi Rex!

Bill Lomas in his article on the Welsh Bantam reckoned it used a single, 60thou (1&1/2mm as yours) ring which was changed between practice and race and between races because it wore out so quick. Point is it "Wore in" and obviously sealed well. I am probably speaking out of turn but my experience in using chrome facing on piston rings is that the chrome would break up with disastrous negative reliabilty... Maybe, half a century on the plating is that much better or the barrel material is more compatible with the "running in" of the ring to barrel.

Major factor, Bill Lomas reckoned, was the way the Walsh Bantam would rev on and on -- that with a megaphone exhaust -- (of course they were using a methanol fuel) -- but the secret had got to be the Reduction of Drag Friction Losses and according to Mackerle who wrote "Air Cooled Engines Engineering" the major source of friction-drag was piston (& ring) to bore (and you probably have the best in piston material with the silicon content...) but I can´t help thinking there are a lot ot other drag-friction sources with the engine-gearbox and transmission -- even tyre tread combined with tyre pressures. Quoted 12 kW loss enine to rear wheel has me wondering where all that heat goes... ??

... Better stop -- you are obviously busy.
Regards to young Nick.
Good luck.

Cheers!

Hi John,

Good Day!

You have a point about friction!

There must be a lot of areas that need study on a Bantam that would give "free horsepower"!

The cylinder plating and ring surface appear well matched!

Top and bottom faces were machined after the bore was finished to get it all true!

Likewise the crankcase cylinder face was trued to the main bearing bores!

On the transmission I have noticed chains can run quite warm and seal "nip" on shafts might be worth a study!

Come on over here--------and improve the Bantam beyond all belief!.....

Do we save frictional losses by limiting the revs also?

Have a Great Weekend!

Rex

I´ve edited this from the original -- dunnknowwhy?

Wish I could Rex ...

-- get over to Blighty, I mean - just no way at the moment ...

Thanks for the compliment but I was never any good at tuning Bantams -- I was too busy with Diesels and only wanted a Bantam to race in what spare time I could scrounge...

Sounds as if you are confident about piston-bore-ring compatability so I´ll try to be quiet ...***

I´ve learned a great deal on here and it probably goes without saying a lot of power is wasted on stirring up THICK oil in the gearbox, using over-tight or dragging seals, plain bearings where ball bearings can be used, chains and other rotating connections out of line. Slick, my Son in the IoM doesn´t tune many two-strokes these days he is deep into preparing racing 4 strokes for Super Stock, SuperBike etc ... etc ... but he spent a lot of valuable tíme years ago testing a lot  of pistons & rings in bores with home-made rigs where he measured the Static Friction of pistons standing in their cyl barrels and measuring the amount of effort required to move them from standstill as well as measuring when moving down and up the bore ... Big point Slick maintains is the piston stops dead at TDC and BDC with the temperature varying at those two situations and does it thousands of times so the Static Friction doings must add up to a lot... and be a big contributor to overall friction losses.

The annoying thing is that where bearing losses are linear with increasing speed the piston drag is an exponentialy rising curve with increasing speed -- which means only a small increase of drag can bring a big reduction of revs. This shows where a high torque, low-revving engine -- of low drag loss thro´out -- can be more competitive than a screamer. I´d quote here the Harley Davidson ride during the Anglo-American Match race series of about 45 years ago when the burbling Harley won and sounded as if the rider (forgotten his name) was on his afternoon ride to Grandma´s for Sunday afternoon tea.

*** some (Bantam people & AB) say impossible!!

Take care!

JayBee.

Cheers!

Hi John,

Good Day!

You have an interest point on the piston friction!

What if we work on the friction side, (make pistons with thinner rings etc) and also improve scavenging etc. for better torque at our low rpm it might be even more competitive?

We have only been developing the cylinder for 12 years, so now might be a good time to get more serious (horsepower)!.................

Just imagine...............24Hp @7500......

Any more ideas when we set that as the next goal?

Have a Wonderful Weekend!

Rex

John,
The American Harley rider from the match-race series, was the late Cal Rayborn, and the Harley in question used the antiquated, all cast iron, side-valve engine. Those facts alone must put Ray`s riding talent up there with the finest of the day!
This engine was superseded shortly after by the more technically advanced all alloy 750cc engine.

One strange phenomenon of the characteristics of the iron engine was that the open exhaust pipes were cut off at 45*, leaving them square cost power? No one at the time could explain this strange behaviour trait of the side-valver and many boffins tried but to no avail. But then how many people can include race preparation of side-valve engines in their CV?

Top marks then to both Harley, and to the Bantam boys for getting good results from unpromising machines with lineages stretching way back to pre-war times.

Trevor

Thanks Trevor!

Cal Rayborn the rider. -- great man of his day which didn´t last long enough...

A good engine tuner pointed out to me about half-a-century-ago, if an engine (4 stroke, of course) breathes exceptionally well during a short period of its working speed range of operation and you can make it breathe even better then don´t bother looking for higher horsepower from higher revs. This bloke ground his own high-lift cams and the engines frequently flew apart yet it was great fun to be around hoim when they worked well.

The JAP engine was an example of high torque over a goodly speed band. At just over idle speed its torque let you know it was there and thumped you in the back. It was a simple engine and had very low friction losses.

Icarus-One Bantam had a zero feel of tractive effort until the revs went above over 5000 ... At 5200rpm there was a feel of push and not much after 7000 although it would rev on to 8400rpm.... Of course, those were early days in the use of expansion pipes and I spent a lot of time at Brands practice getting our sRíght???. and still wonder if it really was right?

And I am still wondering about the Walsh Bantam having a megaphone exhaust and performing so well?

Cheers!

There is one set of changes that may indeed offer free horsepower, or at the very least be a precursor to the “holy grail” of freebies!

Big bore, long stroke, long rod 186 Bantam engines suffer from what might be described as languorous combustion, with additional restraints being imposed by static ignition timing. Unless common sense prevails and a rule change ensues there is little to be done to correct the latter? Duh!
High turbulence is critical to rapid and complete combustion and the prevailing engine geometry compromises this, but chamber geometry is easy to re-arrange. Vital to this is getting a vigorous squish action going to stir the mixture and expose chunks of unburned of gas in the tiny time scale available.
The modified T185 piston you use has a high crown height of 5mm. Comparable race pistons have lower crowns, the 64mm 350 TZ has for instance, 3mm, the Aprilia piston with a 190mm crown radius and taken to 64mm diameter would have a height of just 2.71mm.
Extrapolating the crown surface areas and volumes for the two extremes gives the following;

T185.
Crown radius…………………….. 105mm
Surface area…………….3300sqmm
Volume…………………….8.1cc

Aprilia.
Crown radius………………………190mm
Surface area…………….3240sqmm
Volume…………………….4.37cc

Reducing the surface area of the piston crown will reduce heat absorption so more energy is available for gas expansion to work on crank rotation, and have the additional bonus of a cooler piston.
For a given compression ration the lower crown height means a lower, more compact combustion chamber, also with a reduced surface area to absorb less heat energy. In turn, that means a shorter flame travel, that means faster and more complete combustion, and that means power. Added to that, more heat energy goes into the pipe at a higher acoustic velocity to be exploited to make the pipe operate more efficiently! All of which are plusses!
For a given set of pre-existing parameters and a simple reduction in crown height somewhere between these two examples and with no other engine changes there is indeed “free horsepower” waiting.

Trevor