Pipe Design

Yes Trevor -- thank-you -- I thought it ought to be around 1.35 but was so unsure I went down into our Kellar and dusted off some ancient text books and there -- behold! was a PV example where this clever bloke sorted out a question showing the chemical composition of C8H18 octane (?? he called it that..) which then gave a 15.05:1 A/F ratio by wt -- which seemed exceeding clever and enabled him to arrive at a 1.335 index for this particular example which then enabled me to continue....

At the same time -- in the Kellar -- I found my old 5-fig logarithm tables. That´s because I no longer have a calculator to do log-logs. Yippee! I can still do them!

I´ve got a head-ache coming and am wondering now if it was a good idea letting that Mick Scutt fellow into the fold....

Only joking Mick -- actually I am awakening brain cells that have long been dozing & dormant that were getting ready to slip off their gimballs and fall into the sump.

And memory comes back -- Robby Winston and I, at around 1a.m., looking down on a squatting figure (on my garage floor in Barking) that was snoring. Robby said, "He´s just practising his Isle of Man riding postion....".

You both left at around 3a.m. to go straight to Liverpool and the Island....

Wonderful memories!

Cheers!

Mick!
175°c and 2bar pressure seem rather hefty to me but I wonder what happens when the transfer ports open and the loop-scavenging begins -- in other words what are the real temperature & pressure at the beginning of compression?

175°c plus 273 = 448°K.
For compression ratios of 7.0:1 and 8.0:1 and using gamma as 1.35 as Trevor suggested --
-- the 7 to the index of 0.35 is 1.976...
And 1.976 x 448 = 885.3K -- or 612°c...
--- 8 to the index of 0.35 is 2.0706...
... and 2,0706 x 448 = 938°K -- or 655°c...
--- now 655°c is 1179 + 32°F = 1211°F --- isn´t that getting a bit warm for END OF COMPRESSION TEMP... when the combustion is yet to follow??? poor piston! HELP!!!!

--- anyway, to cut this down to reasonable size -- without the amount of boring calculation -- I went on with it to get to this over-volume filling factor Trevor mentioned (1.4 for a 125 RC & 1.55 fo Apillia, or whatever it was) and with the 25 bhp Mick mentioned along with 2bar poressure at start of compression the number 1.148 popped out -- which is as Trevor said, is suggesting the Bantam could
do with a bit more development -- like something innovative -- hmmmm?

But the 125 Formula -- as it stands -- just would not allow it -- would it??

Hi John

as Derek spotted the figures were for the point when the exhaust port closes ie when compression really begins.

I had read them rather quickly off a graph but as you found them interesting, I have made an effort to measure the graph.

Cylinder pressure comes out a bit higher at 2.4 bar and the temp a little lower than I first thought at 164C

Temperature at the point of ignition is about 420C.

CR from the top of the exhaust port is 7.38

Mick

Hi Mick!
What on earth are you doing -- awake at 4.43a.m. ??

With temp at 164°c (164 + 273 = 437°K) & CR = 7.38:1 the end of compression temperature will be:- (a) 437°K X 7.38 with an index*** of 0.35*** becomes:

(a) 437 x 2.0128* = 880°K or 607°c....

...but because I dusted off the the old text books (last opened in Bristol in 1961...) and found Thermodynamic Tables that told about temperature change effecting that index above with the mix of isooctane fuel C8H18 (guessing there!) in the dry air teh Gamma (ratio of specfic heats at Cp & Cv) becomes -- with a bit more odd calcs and temperature rise** becomes 1.32 ... A further bit of skulldedgery with Absolute temps formulae etc...etc... has (a) with Gamma minus 1 making the index 0.35....

So now, because I went down in the kellar etc... I shall use the index of 0.32 and we can see the difference is:-
(b) 437 x 1.8953 = 828°K or 555°c.....

What follows, which is important relative those differences above, is that the ratio of start and end (absolute) temps effects the End-of-Compression Pressure --

... (a) P2 = p1 x 7.38 x T1/T2 is 2.4bar X 7.38 x 880/437 = 36bar!!

... (b) p2 is 2.4 x 7.38 x 828/437 = 33.6bar!?

That´s 14.5 (bar not Ats!) x = 522lbs/in² --(a)
... and 487bs/in² for (b) ....
...
Of course, in practice there are some losses during compression. These are not accounted for in the above. Also in workinging backwards, as heat supplied from end of compression to end of combustion and my assumption of C8H18 fuel to get back to how much air went with combustion producing 25 bhp that is also assuming stochiometric -- perfect -- air-fuel ratio combustion.

Ah! I just remembered Mick put up another temperature at ignition -- so I have not finished yet ...

Just taking a walk out into the snow as Oates told Scott and his lads -- I might be a little while....!!!`???

***Gamma: The ratio of specific heats Cp/Cv at constant pressure and volume... **Trevor mentioned this when he recommended using Gamma = 1.35....
* 5 figure log tables -- no less!!

Cheers -- I´m looking for the Aspirin!

Hi Mick!
You must have some good instrumentation on this engine????

420°c you said for start of ign.... = 693°K

... (a) with 1.35 index was 607°c (+ 187?) and
... (b) with 1.32 index was 555°c (+ 135?)...hmmmm?

... quite a big difference --- ey oop Trevor! have I binn making mistakes?

So now its a different ball-game

p2 = 2.4bar x 7.38 x 693/437 = 28.1bar --- 407lbs/in²....

OK! so the practical numbers related to the McScutt motor are 164°c(437°K) at start of compression and 420°c(693°K) at the start of ignition ...

That with 7.38:1 compression ratio concludes the surprising "1.27 ratio" of Cp & Cv (specific heat values at constant pressure & constant volume) as being way off what is accepted as the Norm --- 1.35....

IF I HAVE MADE NO MISTAKES then the reason for the difference of 1.35 to 1.27
must mean SOMETHING IS HAPPENING WHICH HAS NOT yet been ACCOUNTED FOR...?? Cooler fuel than C8H14 or more probable large heat loss during compression?

Trevor? what is the CH for Avgas? Or is it that the aviation fuel can be any CxHy
with just the unmentionable added??

What sort of cooling Mick? and what material the barrel?

I apologise for using "McScutt" for your name Mick but it seemed to fit so nicely I could not resist the use. I shall delete... if you threaten to hit me or sue....

Apologies for dragging this out like the hefty flywheel session but some of my latent brain cells*** seem to have caught fire -- as they did with flywheels ....

*** er what????

John - it was only 3:43 am - you are an hour ahead of me

Sadly I dont have the instrumentation on the engine - that would be a lot of fun! The figures come from a simulation which I feel is working ok on an engine that is clearly going well.

I had hoped that giving you the temp at the point of ignition it would compare better with your numbers. It happens to be a watercooled engine but the software does not take that into account.

The best info I have managed to find only says "avgas is primarily isooctane" and goes on to show various calculations on the combustion process - hope this link works, its quite long but looks right up your street -


http://books.google.co.uk/books?id=KEPgEgX2BEEC&pg=PA203&lpg=PA203&dq=avgas+iso-octane&source=bl&ots=irCZ0XyfnG&sig=eHqETSHoCZULp_tKg53QcIok-4w&hl=en&ei=2ou1TrjfCJHD8QOznqylBQ&sa=X&oi=book_result&ct=result&resnum=10&ved=0CGoQ6AEwCQ#v=onepage&q&f=false

Off topic bits -

I've been called lots of things and it doesn't matter at all. At one time the nickname was Sticky - it took a while to figure out it was Mickey Scutt turned around into Sticky Mutt !

I try not to go in for too much nostalgia - what I really want to see is more bantams going quicker. The last race at cadwell was a cracker with Mike Powell, Tom Snow and Ian crossing the line almost touching fairings. It would be great to see some more close racing among the bantams.

To answer an earlier question of course I am dead proud of Ian winning the championship again despite some dnf's early on and riding in severe pain at cadwell with cracked ribs, he's done really well.

Mick

Wünderbar Mick! I thought Sticky was `cos you didn´t fall off --- hmmm too often!
I´ll look at that website later --

Perhaps you are over-cooling ...?? Might account for the change of ratio-of-specfic heats -- or in layman´s terms heat loss during compression which is causing the index of 1.35 to reduce to 1.27 -- according to my
ancient book on Thermodynamics -- anyway ....?

Before going any further I think it might be sensible to mention what you all know but may have ignored in the
rush to get answers.
This theoretical happening to do with ABOVE the piston is the Indicated Horse Power which is much much more than the bhp at the crankshaft output -- in fact the bhp is normally only a quarter of the
IHP. i.e. IHP - bhp = Losses Horsepower. The latter is attributable to mechanical and thermal losses -- some of which appear to have shown by the difference of practical end of compression temperature 420°c and the theoretical end-of-compression temperature being 555°c ... .

I´ll try to put things in layman´s terms:-

The horsepower above the piston -- the indicated hp -- has a thermal efficiency by reason of the compression ratio which is typically 50% and the mechanical efficiency is also typically 50% -- which when multiplyed together gives 25%. Mick has 25bhp and in the worst case that represents his engine´s losses as 75 hp....

Mick´s comp ratio is 7.38:1 which gives a theoretical thermal efficiency of 55%*** and if his engine is skinned to the bone of friction then say the mecahnical efficiency is 65% the overall efficiency is 36%....

*** unfortunately that 55% is based on the Cp/Cv ratio of 1.41 which is for dry air and we have already seen that with a fuel-air mixture that number is typically 1.35 but with Mick´s numbers has come out to be 1.27, meaning -- to my thinking -- heat loss during compression....?

I am being pestered... The sun is shining & She-Who-Must-Be-Obeyed is levering me out of this chair -- must go walkies the sun is shining -- rabbit rabbit rabbit !!

--- but I´ll still try to show what I mean by the index 1.41, 1.35 and 1.27 I´ve been--- using -- later -- if anyone´s interested, that is!!!.

Cheers!

Having just joined the BSA Bantam Racing forum after being away from bantam racing for over 50 years, I have been reading through as many posts as I can to catch up on what has happened since I last raced.
I found a great deal to interest me, but among all the posts where I noted references to pipe designs and software use, with one exception (MOTA) the name of the software used was conspicuous by it's absence.
The software mentioned for designing a pipe unfortunately goes no further than produce the dimensions. Exactly how that pipe will perform when installed on an engine is just a guessing game, it might give reasonable results and it might not.
To get a real understanding of exactly what goes on in the engine ducts when a pressure wave is propagated, a superb 1D simulation package is available that will open the eyes of anyone who previously has not observed the wave actuation that takes place. Details of the software, EngMod2T, can be found on Vannik Performance website.
I must say I am surprised that contributors to this forum who have made very frequent postings where software has been mentioned, have it seems, deliberately avoided mentioning the name of the software used.
Whether someone wishes to use software is of course up to the individual, but at least knowing what is available is helpful when making a choice.

prorad,
Welcome to the Forum, and it is indeed a pleasure to re-discover a fellow enthusiast from 50 years ago, we may even know each other and have competed in the same races, I started in 64. If you would care to identify your-self we may be able to confirm that or not?

Just before making this post I Googled to find "two stroke simulation software", Neels` EngMod software was easy to find, so no secrets there, and I am equally sure that most Bantam race enthusiasts will have done the same. But also, there is no need to repeat what is already common knowledge? As always with any computer software where multiple inputs are required....... garbage in = garbage squared out......., so it`s not for everyone.

I`m sure we shall all look forward to your continued contributions, photos and reminiscences, from the old days, are especially enjoyable and warmly received.

Trevor

I have searched the posts but so far failed to find any reference to exhaust systems that feature a 2 stage reverse cone.
It could well be that this has been tried by members, but if so they have not mentioned it on this forum.
To make such a modification for test purposes is relatively easy and cheap (if you do the work yourself), and if the end result is not to your liking the original cone can be re fitted.
There is some merit in investigating this modification, as the benefit is most always to be found in an enhanced boost in power through the mid range, with little or no drop in peak, although the over run past peak is likely to be reduced.
Those possessing an engine simulator that can handle such details can easily lose themselves for hours at a time running through various permutations (and possibly lose themselves in more senses than one if not careful). If, after all the trial and error simulations the indications are still good for a certain modification, then it is worth the effort to make the change.

Sorry to mix topics, but a much older post made reference to the use of methanol in a bantam ( post came from Australia I believe). Methanol for an iron barrel engine is a good choice, although it has been very sucessfully used in alloy barrel engines, and water cooled ones also. I had many years experience using methanol in MX two strokes. part of a sucessfull conversion from petrol is to ensure that the annular flow gap between needle and needle jet is greater than the flow area of the main jet - otherwise instant hole in piston. The Bert Flood 350 air cooled Bultaco that Ginger Molloy used to ride makes 68 rwhp on methanol, and the exhaust features a 2 stage reverse cone.

Hi ProRad!
I spoke about methanol several times on here because I used it extensively to pleasant advantage in several motors grass tracking, including a 1937 - 250AJS during the 50s - 60s era. The (Aussy) Walsh bantam was on 16:1 and my 500JAP on 16.5:1 compression ratio... I published, on this site, the theoretical Thermal Efficiciency versus Comp Ratio whioh shows the advantage from 7:1CR to 16:1CR to be 14% -- 53% to 67% -- which a lot tuning competitors snatched onto, yet the Walsh Bantam, using a megaphone pipe made many Aussies look silly which I think was down to a reduction of friction drag within the engine & transmission: as for example, using a single, 60thou ring which was changed between practice and racing. Bill Lomas´s magazine article mentioned this and a copy of that article is also somewhere in these BRC files.

I am a bit lost with `reverse-cone´ reference, surely that would be the resonant exhaust system we were all using and the lads are still using -- wouldn´t it?

Cheers,

JayBee.

Hello John
I always found methanol a relatively easy fuel to use, provided of course that carburrettors were suitably modified.
On cold mornings it could be difficult to get the motor fired up, but once a little warm there was never any further problem.
A two stroke on methanol will run well even if quite rich - often so rich that the rider would think the engine was trying to seize when running flat out, but closing the throttle perhaps 1/8 inch would have the engine immediately pick up more revs,
thus confirming the excessive rich setting.
The use of methanol was occasioned by a restriction on the use of petroleum based fuel for competition events back in the 70's. An application to use methanol as an alternative (being vegetable based) was granted by the government, so with the change MX continued unrestricted. This was in South Africa.
A thermocouple in the exhaust header showed the exhaust to be somewhat cooler than when petrol was the fuel. In theory it was possible to run more compression, but when thus modified the results showed little or no worthwhile increase.

The 2 stage reverse cone I was referring to was for a fully tuned exhaust typical of that used by most top two stroke engines. My own experience of it is with a very modern engine that unfortunately did not make the race tracks in time, and now never will because of the switch to 4 stroke power (Moto 3). This engine had three exhaust ports, one main and two auxiliaries, and the shock wave generated at port opening was colossal. I have not been able to compare this directly with a bantam engine of any capacity, but I doubt a bantam would be anywhere close in this respect. If this is indeed the case, then perhaps a gain would not be so significant. The Bultaco I mentioned has a bridged exhaust, but has been heavily re worked. The output I quoted was in error, the figure of 68 hp was measured at the gearbox output shaft, not the rear wheel as stated. Ginger Molloy is getting on in years now, and is not so hot around corners any more, but when he gets it upright and pointed down the straight, it's speed is just awesome

Rad

As part of the 2007 re-vamp of my w/cooled engine a two stage rear cone, replacing the original on the existing pipe, was tried. The steeper of the two cones was placed at the junction of the tail-pipe, it was 25% of the length and had an included angle 5* greater than the remainder of the cone. There was no science behind these numbers, just an empirical starting point, or if you prefer......suck it and see! Full of enthusiasm and optimism we tried the bike, after a bit of fiddling with the variables of adjustment, carb, ignition etc, the conclusion was; no difference, nothing that could be measured. Mark had the feeling that the power band could just have been coming in a touch earlier but was at an rpm level not used much during actual racing.
It would be interesting to hear from anyone else that has tried a multi-taper rear cone to gauge their experiences.
I concluded that with so many other areas of pipe design to explore that almost certainly do alter performance this avenue was one best left alone.
It would also be of great benefit to have someone explain, as they see it, the exact influence multi-cones have on wave energy that can produce the suggested power level gains? It might just be that an increase is achieved in pipe volume and that the Helmholts resonance frequency is lowered and causes a smearing of power band width, but at a cost elsewhere in the power delivery characteristics. I don`t know, but it`s fascinating all the same.

Trevor

Got it -- thanks. First time I heard of the rear cone having double angle of dangle! Firts time I heard of such a thing...

Had enough practising at Brands with the simple resonant  pipe  at different sizes of cone and distant apart -- lord knows how many I made and dumped....

Maybe the tailpipe-cone should be a hemispherical shape as per the Helmholz theory.... ? could make for a lot of fun on the dyno  

Uh oh! Yeah -- OK -- I'll shuttupp and go away....

There are a few examples in Graham Bell's book of designs with two reverse cone sections, but the angle changes are relatively small. The Bultaco reverse cone section was 300 mm overall, the first section was 220 mm long, starting at 115 mm and ending at 76 mm. The second section was 80 mm long, and continued from 76 mm down to the tail pipe diameter of 33 mm. The included angles were 10 and 30 degrees respectively (give or take the odd minute).
The pipe was not my design, and I have no idea whose it was, possibly Bert Flood himself.

I would be interested to learn what horsepower a very good 125 water cooled bantam is making. I have found quite a few oblique references, but no one seems willing to divulge their engines capabilities. I can to some extent understand that one would not wish to give too much away to the opposition, but a general figure would suffice. Is 30 rwhp being exceeded ? I would like to think so, in fact I would guess a figure nearer 40 would not be out of place. Anyone ?

Rad,
One thing is for certain, there will never be a Bantam engine that produces 40 rear wheel horse power, ever! A tiny number could, just possibly, approach 30 with extensive re-structuring to remove the old BSA innards of the barrel, but the vast majority, be they air or water cooled, will stall at around 20/22/23. The air cooled iron engines are always at a disadvantage and will never finish a race making the same power that they started it with. Same applies to the alloy ones but to a lesser extent. The simple physics of engines demands that with all other things being equal, a temperature rise equates to a power fall, water cooling wins hands down.

I can sim my engine, with the right pipe and ignition curve, to 32 crank hp, deduct 15% for transmission losses, that leaves just over 27rwhp, but is that realistic, probably not! Dynos however, give such variable results as not to be relied upon from one day to the next, one guy admitted to getting readings differing from 23 to 27 for the same engine, take your pick?

Don`t place too much faith in Bell`s old advice where pipes and ports are concerned. He was fine for his era but there has been so much development in the last 5-10years that renders so much of his advice obsolete. His one size fits all approach is no longer realistic.

Trevor

Trevor
Thanks for your reply, at least now I have some idea of the current situation regarding current bantam racing engine development.
I totally agree with your comments re the unreliability of dyno test results, for many years now I have only used a dyno to provide a check that the engine performs without any detectable problem over it's required working speed range. If it is making sufficient power it will be obvious when put to use on a race track. if you are a winner you have sufficient power, the numbers are immaterial!
Bells exhaust pipes were mentioned because some were featuring two stage reverse cones. Like yourself I don't consider anything in his book is of any particular relevance to the current situation.

I did specifically mention a water cooled bantam in my previous post. I am well aware of the limitations of an air cooled iron engine when it becomes virtually heat saturated, and am not considering such an engine in my present deliberations.

I would expect a home constructed water cooled cylinder to have a three exhaust port arrangement, a main port with two auxiliaries. I would not be initially looking for any additions to the standard two transfer ports, and a piston ported intake would be an appropriate starting point. You yourself have built such cylinders, so are well conversant with the work involved and the problems to be overcome. With a well designed combustion chamber and squish control, combustion efficiency of 95% is possible, and if it's not then something is amiss.

This is all too easy to write about, and the practicalities are another matter entirely. I would respectfully suggest your estimate for transmission losses of 15% is rather too much when converting sim engine power to rwhp, but if it's a constant then good - at least it is not a variable like a dyno run so often is.

The one great advantage for sensible use of a sim over a dyno is - the dyno may indicate the worth of a change, be it for better or worse, but it will not be able to reveal the reason why. The sim results can be analysed in considerable detail for such purpose, and all too often some really fascinating details are disclosed. Here lies the real key to understanding the physics behind a two stroke engines function, and it's from this understanding that one might get the glimmer of an idea that can be the beginning of the next positive step forward.

When the sim results match the dyno runs and combine with race wins - then you've hit the jack pot!

Of course Trevor, to you this is old hat, but there may be some who are not aware of just how powerful a tool a good sim is in engine development work, in fact computer simulation has been in use for some years throughout the motor and motorcycle industry in general, particularly in race engine development.

Rad

I used Victor Martin Track Fuel when grass tracking and also used Methanol in my 1927 Triumoh 500 at Cadwell and Brands. Rather crude conversion -- I have to admit --  up the Comp Ratio and  bore out the Amac´s mainjet with a 1/8" (not yet converted) drill. Starting was brilliant but I hadn´t got round to doing anything with the gearbox and I was forever stirring up the box with the long handle up at the tank but it gave a bit of fun because both times was racing because  I was swapping places with an Inter Norton at Cadwell and a  Rudge at Brands ....

 Victor Martin Track fuel had 1.5 to 2% `Puridin´ added to an unknown base fuel .  I assumed  Puridin was TEL and wondered what the base fuel was? Anybody know anything about Puridin? it must be the trade name for a TEL addiitive.

  By the above you understand I was not good at bike prep and only wanted to race ...

  That  thing of how much power  is lost to transmission -- like say, 12kW -- has me wondering where does all that heat go? Like having a dozen one-kW fires burning up your whatsit -- gotta feel warm!!?? ...  yet I must repeat  the quote of an example in the text book by Bevan in "Theory of machines" -- 1936 -- where the motorcycle (in the example) transmission efficiency was said to  88%  between engine & rear wheel. That 12% must have been improved upon  since then...

 I would argue that dyno testing is most advantageous in terms of comparing max power and the torque curve SHAPE -- providing correction factors are used. Because we didn´t have a dyno it was comparison of testing at Barnds and,  of course, I was not correcting for ambient conditions -- except perhaps the wind...
 I hear fantastic dyno horsepower numbers and never hear what Correction Factor was applied...  
  A bumpy torque curve is preferred by some top star riders than the all-out top-end  power. I would mention Carl Fogarty on the twin Ducati in this respect at Hockenheim when he sat behind Ayran Slight (Honda  4 cyl )for a whole race except for the last bends in the Autodrome when he   accelerated past Ayran Slight just   before the finish.

  There was also the time GP Champ Valentino Rossi was  on the Ducati and couldn´t do a thing right all season  so the argument that the way the power comes in and how a rider can keep the power on thro´the bend has the torque curve shape coming into predominance in the equation....

 Cheers!

Rad
    Yes, the 15% deduction from crank to tyre is too high, but I am happy with that, it includes a factor for those other little areas in the sim that can`t quite be quantified, a little reality check! No matter how accurate the measuring of the data to be supplied to the sim program there are always those areas of uncertainty that can be over-optimistically estimated. For instance, actual flow rate potential for us garden-shed tuners is impossible to accurately determine, never more so than with the transfer scavenge regime. Human nature being what it is, its far easier to fool ones-self than any one else, and software packages still offer lee-way for idiocy to creep in and still get a result!

Rad, I would urge you to review your suggestion to work with only two transfer ports, particularly as you advocate a triple exhaust port arrangement, you will get a huge miss-match in the STAs. Two transfer ports with a huge triple exhaust port area will almost certainly lead to severe short circuiting of scavenge flow. Particularly if you couple that with an efficient pipe that sucks like hell around BDC when the transfers are flowing at their maximum.
Piston inlet port is fine, but for a Bantam, a reed system provides a much wider power band and a more generally well behaved engine, both of which are essential with only 3 gears available. In addition, it facilitates the introduction of extra, valuable, transfer port area.

I don`t, myself, use a combustion efficiency quite as high 95%, despite water cooling. Bantam barrels don`t shed heat as fast as pukka, all-alloy Nicasiled race engines, so compression, ignition settings and carburation all reflect the limiting thermal factors inherent in converted iron barrels. These factors in turn tend to compromise clean, efficient and rapid combustion, so again, I try to reflect the more modest reality of Bantam racing!

If you would care to PM me your e-mail address I could send you some pictures that show the porting and general construction arrangements I use for my water cooled engine, that will give you some idea of what the current thinking is being applied to UK Bantam race engines, or at least to some of them!

By contrast, I love John`s anecdotes about his colourful race exploits. I can just see him speeding around Cadwell, struggling with the uncooperative gate-change mechanism up on the tank of his doped-up Triumph, barely in control and scaring the opposition into submission! Thanks John.

John, might you be thinking of Pyridine, a highly flammable liquid from the Benzine group of chemicals, and not Puridin which is used in the pharmaceutical industry for the manufacture of oral capsules? At least that is what I found out today!

Trevor

Trevor
my estimate for losses between sim engine power and rwhp is 12%, not so far off from your 15%. Either way, the difference is no big deal.
Your comments re the need to consider 4 transfer ports comes after I had already gone there, but thus far I am still working around the piston ported intake. I will get to the reed block eventually, but right now I'm having fun with the existing data set.

A middle order engine should present no major problems to a workman who exercises care in his use of tools, and has a range of workshop equipment at his disposal. Getting on to a top flight contender requires something extra. There comes a need to work very precisely to dimensions, and 'near enough is good enough' has no place in this exercise.
Static clearances change with running the engine, for instance squish clearance can be very different when the engine is at full throttle than the cold setting. The ideal squish gap is zero plus the barest fraction to avoid metal to metal contact. To establish just how close the piston gets to the head I use a centre punch and 'pop' the piston crown at four places around the area under the squish. This raises a tiny rim (like a minature volcano crater) which can then be measured with a vernier to determine it's height. If after running an inspection shows no contact, then the dynamic squish clearance is at least the height of the rim.

The notebooks I made during over 60 years in all forms of racing total 17 to date, but during moves around the world 3 have been lost, including the first one where my bantam details were written up. Try as I might, there is much about that machine I can no longer remember, but I still have a few photo's, if only there was a simple way to post them

Rad

Thanks Trevor!

It was a bit like you described - the flag moved and three of as if tied together  were rushing at the Cadwell Club hairpin -- a Scot on the left  a Rudge on my right.  Quite odd that we were all together on the exit. I changd into second -- missed the notch, went into top (only 3 gears, on a `27 Triumph,  of course!) wrenched it back where second should be and the Scot & Rudge were into Charley´s and I was about 7th coming out of Charley´s ...
Thing was, on my first proper Vintage race I finished in front of a lot of weathered-veterans on better machinery than my old triumph...

Girder forks, long wheelbase and solid (really solid) backend -- so what might be so wrong  in having a  Bantam with solid back end? Most circuits are smooth and you can feel the road much better without the cissy springing....


Re the addiitive. Thank you, Trevor. Pyridine it could have been because Í never saw it as the written word and the Cherman´s often sound the `y´ as  `oo´  (more like our u without the y... as in psychiatricker -- sookee-atriker!). On my 500 JAP the additive  meant the difference of an 850 main-jet instead of 1100 on straight Methanol.
That engine must have had a flat torque curve or it might have been the quick-action throttle that had it flip backwards off the line... ? and  there was always a kick up the back no matter the throttle opening.

A serious part of race tuning is to reduce the friction drag -- engine to back tyre -- to a minimum which many  
know about `how-to´ but hardly ever mention,  and even then in whispers to best buddies.
  In the engine it is, of course,  mostly piston and ring, then bearings -- plain to ball --  with seals also contributing a considreable amount. If there were no friction losses the engine would rev on and on...

that last commentb should bring a response ................

Cheers!

JayBee.