Nothing from Something

Nothing from Something

The nothing here being any meaningful benefit, the something being air pressure. So where is this all leading to I hear you ask?

Lockdown, at least for us here in Somerset has been almost total, one visit to Taunton NHS hospital for another CT scan and one to my GP for more bloods to be taken to further inform my consultant as to my present condition, and a subsequent phone conversation to discuss the findings.

To gainfully utilise some of the excess of spare time imposed on me I`ve been back to around 1965, when I joined the BRC, and right up to the present day by trawling through my archive of Bantam stuff and engine stuff in general, two and four stroke, both as drawings, documents and magazines/books and even letters, and in digital form here on the computer.

One topic that did arouse my interest from all of this endeavour, and one which hitherto I had paid little heed to, was that of `Ram Air` induction augmentation, the `something` from the intro. Stimulus came from two, torn out pages of examination by the always readable Kevin Cameron in Cycle World magazine. The topic was the emerging popularity of utilising the potential of ducted, high velocity air. Kawasaki and the other manufactures of large capacity multi cylinder bikes from Japan used the system to improve machine performance and so enhance sales. A cynic might suggest the whole thing was a `rider placebo go faster gadget`. Several Bantam builders over the years have toyed with the idea but I`m not sure these notions ever reached fruition, however, please post your experiences and findings if you have indeed succeeded, it will make interesting reading. Actually at the last get together of the Midlands group in Gloucester this topic was touched upon and one respected rider/tuner suggested he was going to have a go, no idea if this ever actually reached fruition?

The question posed by this seemingly attractive proposition then is, could this technology be of benefit to our humble Bantams? Something for nothing perhaps, that’s difficult to ignore but there is little similarity between mighty, multi cylinder four stroke engines and our modest, little home tuned two stroke Bantams, is it really a viable proposition?

For `ram air` to work air velocity has to converted from dynamic to static pressure, This is achieved, counterintuitively, by slowing it down, the kinetic energy of the moving air is traded for an increase in internal energy (conservation of mass). The big problem here is that up to around Mach .4 air is considered as incompressible, so, as kinetic energy cannot compress the air so there is no pressure increase.
If you are so inclined you can work out the theoretical pressure benefit, using the SI units, by the following, .5 density x velocity^2. So roughly at 160kmh (100mph) you get 1.2kpa or 1.2% more ambient pressure, not a lot then. But, as we have to factor in the temperature effects on air density and barometric variations, a fudge factor has to be included so only about 85% of what you start with becomes available so we end up with just 1% gain, or 10mb for those who prefer the old system. That is of course just doing the theoretical math, the reality of getting the air from where you gather it and then into your nice, sealed air box is another matter altogether. Looking at this from another perspective, you can get the same result by reducing air temperature by just……….2*c.

It would be nice to think that whatever little can be gained at 100mph could still be there at a lower speed. Sadly that increase is proportional to speed squared, so at half speed you`ll only get ¼ of that achieved at top speed.
The basis of this article assumed a potential of 100mph for a Bantam, knowing the types of circuits raced on these days I would doubt that Bantams will reach that speed for any meaningful distance that could enable the ram system work. The sad reality is that in the world of fluid dynamics Bantams are just too slow to take any meaningful advantage of ram induction.  Further complicating things is that ram systems plays havoc with carburettors, jetting and float chamber function with air pressure fluctuations oscillate wildly.

So is all of this worth the effort, NO is the answer to ramming, but very definitely YES to an air box. As big as can be fitted, fully containing the carb and vented to a cool air source at ambient pressure, but not from inside the fairing that air is way, way too hot, especially if you run a high level exhaust pipe.
If you are ace, race and on the pace of this, shove an ice pack into the roof the air box and breathe turbulence free, cool, dense, oxygen laden air into the engine, now that really will be something from nothing.

Cheers, stay safe, it`s not over yet by a long way!

Trevor

Apologies to you all, I didn`t do my homework as thoroughly as I should.
Back in 2012 Dan Sofield installed a ram system directly into the carb bell mouth on his 175, sadly with unfortunate consequences, his experiences can be viewed here on the forum. Mick Potter`s subsequent diagnosis was, as is usual for Mick, analytical and instructive.
The small overpressure at speed is enough to depress fuel in the jet block and influence the float level and force the engine to run weak but at slower running doesn't have the same effect.
Upon further reflection it might have been Mick himself, at the last Midlands meeting, that was thinking of a ram system for his own Bantam, if so, did you make any progress Mick?
At one time Steve had a `sealed` air box system on his 125 RS which was fine when it was sealed but overall was more problematical than was worth the supposed benefit. The fuel tank was connected to the air box but the piddly little connection tube proved to be inadequate but easily remedied with a larger diameter pipe. Having to work on the engine was a total dismantling job so in the end was abandoned with no discernable ill effect.

Keep clear of the bugs, maintain best practice and stay safe, there is a killer out there!

Trevor

Trevor,

Your article has reminded me of how I stopped my air-cooled motor going off in a 10 lap race. (typically fastest lap was lap 2, and it was downhill after that). This was in mid 1985 and we hit on using some Ford Granada Zip tubes to duct ambient air from the nose of the fairing to either side of the Mikuni carburettor bellmouth. I tested it one Wednesday afternoon at Brands, with a type K thermocouple near the bellmouth and a readout taped to the tank. With the tubes blanked off at the front, I was getting up to 30 C after a few laps. Untape the ducts and it was brought down to 21 C. The ambient was around 19 C I recall. I was having trouble getting the better of Bernie Webster on Gerry Pell's water cooled Bantam. After implementing this measure my lap times were much more consistent.

More when I next visit!

Peter

We are guided by the science! That is the mantra we get almost every day from our politicians but who seemingly then take no heed of, perhaps they could learn a lesson or two from Peter.
His anecdotes utilizing the “appliance of science”, in this case basic physics, affirm that cool air entering an engine will produce more power and reduce engine operating temperature than ingesting hotter air that is well above ambient temperature. In that scenario, hot inlet charge is far less dense and so has reduced oxygen level and consequently, makes less power.
Pete`s clever and innovative thinking behind getting, something out of nothing, is an example to us all. Trying to keep an iron Bantam engine cool and running efficiently is always an ongoing challenge, and Peter was better at that than just about anyone I can recall.

On one occasion at Cadwell, Mark, riding the water cooled Bantam was well out in the lead when the engine began to slow and got progressively slower, he did just manage to finish the race. A post mortem in the paddock revealed one wire connecting to the electric water pump had broken, and so as the cooling water flow all but stopped power decayed in step with the excessive heat build-up. There must have been just sufficient thermo-syphon action taking place to stave off a nasty seizure, together with the fact that the engine always seemed to be running over rich. The one benefit of this is the provision of a degree of internal cooling where hot unburned fuel was ejected into the exhaust system. We also have good reason to be thankful for the extraordinary lubricating properties of Castrol R40.

The problem mentioned of the over richness was not simply a case of too large a main jet. All carbs of the type generally used on Bantams utilise an air correction system, which comprise normally of cast or drilled holes leading to the jet block. On the Amal we used, both the air jet and idle jet entrance holes are in the curved bell mouth forming an elongated oval entry. As air velocity increases over these holes they are subject to a negative pressure which is exactly opposite to what the carb needs to prevent increasing richness. The idle jet however is not as drastically affected as the air jet. Once I had clocked what was happening, and it took a while, the remedy was quite simple to effect. A short length of very thin walled bass tube was inserted into both bores, extending to just over the entry edge of the bell mouth, a small fill of Devcon blended the exposed tube o/d to the curve and all was done. So at last, the main jetting responded reliably to a size change, and the engine ran all the sweeter for it.  
Trevor

Hi Trevor, just as a small matter my endeavour was not really ram air or a full pressure system, but rather making cool air in the area on the carb mouths, it went bang that because of a calculating error on my part most likely thinking I'd used the diameter but actually using the radius when building the head squish band giving me a healthy 16:1 compression, needless to say it only lasted two laps I think lol

Hi Dan,
            16:1 , ouch, yes that would do it alright. Never been that high, I did go to 15:1 in a 56 bore 125 but there was so little cylinder filling and mixture retention in that set-up that the dynamic comp ratio was so low that we squeezed the hell out of what meagre amount of fuel was trapped.
Your situation back then can`t have been helped by having to run a non-retarding ignition set up, a pretty archaic regulation that served no one well.
Ducting high speed air to the vicinity of the carb bell mouth can`t have helped your situation either.
The overall learning curve is oft times steeper than anticipated but we`ve all been there and have the wreckage to confirm it.

Cheers, stay safe,
Regards, Trevor