Was the 1961 Domi racer 500 a short stroke?

Rohan, If you have a few 650cc Triumph parts, you can easily build yourself a short stroker. The crank costs $2,500, and the 9 stud barrels can easily be shortened by 12mm if you tap the stud holes a bit deeper. It is an exercise which might do you a lot of good.

???
You just told us such bikes were rubbish.
Doug Hele might disagree.

These days, you can buy stronger bikes brand new out of the showroom.
Come with an electric leg, a warranty and BRAKES !

We are discussing short stroke twin cylinder bikes of the 50s. The Hannah Paton was the best known and I believe Geoff Monty had a good unit 500 Triumph engine in a Ducati frame. I raced my short stroke 500 for 12 years then I rode a decent manx at Calder Raceway and found I was about 5 seconds per lap faster with a top speed of about 5 MPH slower. I've never found any bike which could destroy confidence quicker then my Triumph. The manx slightly over-steered and had plenty of torque, so it inspired a lot of confidence. I found I could ride it very hard without any anxiety - the Triumph was obscenely different. The domiracer had a longer stroke than my Triumph and was probably OK. It is an expensive exercise to build one and then find out it is nasty and horrible . When you talk about international riders of the 50s such as Tom Phillis, you are talking about a different breed. They were usually brought up on rock hard tyres and intractable bikes. When those bikes went around corners they were almost vertical. As soon as you try to race that old garbage against the two strokes of the 60s, you find out the reality.
A short stroke twin is exciting to race however I don't need that much adrenalin, and it doesn't help me much remembering those days when I crashed at many meetings. The Seeley 850 is nice and safe - it is not rocket science.
I don't consider myself to be a good rider - you don't become good by racing a bad bike. There is one thing though that I am very good at and that is surviving. My Triumph taught me that. If it rains on race day, I am laughing.

quote;
The change to a 650 type crank for the I.O.M 1961 TT was to use larger diameter bearings and stiffen the crank thereby. The timing side ball bearing was also replaced by a larger roller bearing type, and upon stripdown after the race it was found to be breaking up. That and the rear tyre fouling due to fling at high speed no doubt contributed to the Domiracer's rather dissapointing showing, but surely says something for Tom Phillis' ability to coax it home into third place.[/quote]

It is often forgotten that Phil Read rode the 500 Dommiracer in practice for the TT, but opted to ride his own 500 Manx in the race.

Bernhard said:

quote;
The change to a 650 type crank for the I.O.M 1961 TT was to use larger diameter bearings and stiffen the crank thereby. The timing side ball bearing was also replaced by a larger roller bearing type, and upon stripdown after the race it was found to be breaking up. That and the rear tyre fouling due to fling at high speed no doubt contributed to the Domiracer's rather dissapointing showing, but surely says something for Tom Phillis' ability to coax it home into third place.

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It is often forgotten that Phil Read rode the 500 Dommiracer in practice for the TT, but opted to ride his own 500 Manx in the race.[/quote]

And also reported that he chose to ride the Manx because the Domi spat him off in practice due to an abrupt power band.

If you look at photos of the Domiracer you can see why. The header pipes are too short. (My opinion based on 5 years of dyno testing and racing of 500 twin Norton engines.)

johnm wrote

If you look at photos of the Domiracer you can see why. The header pipes are too short. (My opinion based on 5 years of dyno testing and racing of 500 twin Norton engines.)

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Amazing. Next you'll be telling us you can deduce the valve timing by an estimate of the length of the wheelbase.!
You should get together with acotrel, he spent 12 years learning how to build a rotten Triumph. The two of you combining your 'talents' could surely show us all where we've been going wrong these last few decades.
We should all give thanks that Doug Hele was a very gifted motorcycle design engineer, and he worked from sound engineering principles - not vague flights of imagination!

John has previously documented, in excellent detail, his racing exploits with his dommie 500.
Including dyno charts of tuning it along the way.

Edited - in the interests of a harmonious forum !.

Snotzo said:

johnm wrote

If you look at photos of the Domiracer you can see why. The header pipes are too short. (My opinion based on 5 years of dyno testing and racing of 500 twin Norton engines.)

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Amazing. Next you'll be telling us you can deduce the valve timing by an estimate of the length of the wheelbase.!
You should get together with acotrel, he spent 12 years learning how to build a rotten Triumph. The two of you combining your 'talents' could surely show us all where we've been going wrong these last few decades.
We should all give thanks that Doug Hele was a very gifted motorcycle design engineer, and he worked from sound engineering principles - not vague flights of imagination!

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Sorry - What a terrible person I am My children will be scolding me for being a troll

Actually I wouldn't be surprised if you looked at the development of wheelbase and valve timing over the years you may find some sort of correlation. But then as they say. "Correlation is not necessarily causation."

First off. Of course Mr Doug Hele knew a thing or two or three He was a professional engineer who worked in the industry for 40? years. I'm a part time hobbiest.

But what I can add is this.

When I started racing my 500 Dominator, (standard bore and stroke) I collected every bit of information I could find on engine set ups including exhausts cams etc.

For the Domiracer I estimated the exhaust dimensions by scaling off photographs.

I then created a set of test exhaust systems based on all this information, I made the exhaust and inlet systems telescoping so I could test lenghts. I also tested at least three header diameters, four different megaphones (including a hollow Commando muffler which worked rather well!) plus two silencer cans. (Something Hele did not have to consider)

After about four years, 100 plus dyno runs, 200 races, three NZ Club titles and two seconds in the NZ Classic Senior TT Im very confident that in my opinion the Domiracer would have had a wider power band if it had used longer header pipes.

I put a lot of the graphs from testing on the Britbike forum over the years and a few here.

If you read what I said again carefully I did not say the Domiracer would have been a better TT bike with longer headers. That is a different kind of race to the short circuit sprints my bike was running in. I just said it would have a wider more controlable power band.

Please note what I am saying is not novel or unusual. Any of the standard texts will tell you the same thing. Smith and Morrison or read the chapter on empirical tuning in G Blairs Four Stroke book. Standard plain normal exhaust tuning - Longer headers tune over a wider range of frequencies hence wavelenghts.

If you wish to investigate this further play with the exhaust options in the freeware single cylinder engine simulation package offered by Lotus. Pretty amazing for free software.

http://www.lotuscars.com/ro/engineering ... g-software

I think Doug Hele might have liked it

A standard bore and stroke dominator would be a much nicer thing to ride than a hotted up 65.5mm stroke T100. If there had been an easy way to get six speeds close ratio into one, it would have been worth playing with. I've just been reading Michelle Duff's book 'make haste slowly', it is interesting what he says about gearing. While a lot of guys gear for max speed at the ends of the straights, he used to gear for max flexibility on the tighter parts of the race circuit. What you gain down the straights is nothing like what you can pick up by outriding others around the tight parts of the circuit. The short stroke twin demands 110% riding at all time, and is essentially a very top end motor. With my Triumph 500 and it's 4 speed CR box, you could choose where you wanted to lose a race. If you gear it high, it is good on the long parts of the circuit however gets thrashed around the tight bits. I only ever had one really good ride on it. That was when I dropped the gearing right down as low as possible, and I blitzed a field of superbikes and two strokes around most of Winton Raceway. I was passed by three desperate riders at the end of the straight when my bike ran out of puff. Then the guys on front of me found they couldn't get around the next corner. So I pulled my bike up out of it's lean and speared off just missing a couple of them. I'd always tell anyone wanting to go down that path that if you haven't got the gearbox- forget it. Otherwise it is worth doing for a lot of fun and a big adrenalin rush. It is one of the reasons that I am so silly in the head.

johnm,
your explanation of your involvement with your 500 Domiracer is very interesting. I must confess I had not read any of your previous posts.
You will undoubtedly have come to understand as a result of all your tests , that there is usually more than one way to get a desired result. Back in the days when the Domiracer was under development, the target was to produce a machine suitable for the TT. Had further development been agreed by the Norton board, no doubt other configurations would have been explored, but in those days the British Motorcycle Industry in general was extremely complacent (and at board level incompetent) and were of the opinion that spending money on additional development was unnecessary, as what they had was good enough. Doug Hele had a little more room within which to maneuver when he went to Triumph, but not much. Doug Hele would undoubtedly have liked to use such software as is freely available from Lotus, but much better is the EngMod4T software, and although not a freebee,is extremely good value for money, covering as it does all engine configurations from a single cylinder up to a V12.

I am also well aware of the work of Professor Gordon Blair, he was a friend for more than 40 years, and I worked closely with him on some aspects of his 4Sthead software.
You will no doubt have come across his comments in his book about the development of the long G50 exhaust, which at the time was intended to enhance the midrange power, but on test was found to boost the top end by a considerable amount. More than one way of getting a result - not the result he was looking for, but he only discovered the real reason behind it some ten years afterwards.
I was also fortunate enough to know Doug Hele, and also his AMC counterpart Jack Williams, both real gentlemen. A pity the world has not more of their kind today.

And for rohan,
I was probably racing before were born, Triumph 500, GoldStar 500, Manx 500, G45 (now THAT had a b... awful power band). I have been involved in racing of some form or another for over 60 years, and am still involved, but now only in a design capacity, specifically valve gear in all it's variations. My involvement has taken me around the world a good few times with two strokes and four strokes, two wheels and four, and in shore power boats (Mercury V6 two stroke).
What have I learned in all this time ? Two things, firstly, to measure is to know, and secondly, always keep an open mind.
And no, my name is not Mr. Gradler.

Edited - in the interests of a harmonius forum.
Keeping an open mind ...

Sorry to disappoint you rohan but the answer again is 'no'

Sorry, my mistake.
Carry on !

Hi Snotzo

I searched for a post where I loaded some of my graphs but this was the best I could find - only a short sumary. The date is Sunday July 28 2013.

dyno-questions-t16939-60.html

But for the past 3.5 years I have been sent overseas by my company and have nothing new to report. I have read many of the authors you mention and was lucky enough to sit with Peter Williams for several hours talking about Norton tuning. I have had bikes since I was 15 and my farther was an ACU clerk of course etc before that. He was a friend of Percy and Rod Coleman in NZ back in the 1950s. But I was only activily involved in racing in my forties once familly etc were settled. During that 10 year period I "stole" everything I could find written or reported by Hele, Blair, Irving, Jennings, Cameron, Vizard, Bell etc. The G 50 long exhaust discussed in the Blair book was indeed one of my models. Thankyou for the information on the software.

The NZ tracks are almost all short, tight circuits where engine flexibility is most important. Thats what my bike was developed for under clubmans rules. The Isle of Man is something different. I shall be at the Manx GP this year helping friends who are bringing a bike for the Classic Manx from NZ. First time for all of us except the rider. It will be interesting to see if we can get a finish!

Regards

John

Rohan said:

Edited - in the interests of a harmonius forum.
Keeping an open mind ...

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Glad to see you are learning, however the information is probably wasted on you. I suggest you should read Michelle Ann Duff's book 'Make Haste Slowly'. I found it to be very reaffirming. The write-up on the Porcupine is very interesting. The whole book is credit to him/her, it is very candid and revealing. I was amazed when I watched the Youtube video of him racing the 7R AJS against the 350 MVs etc. I would not have thought the AJS would be anywhere near them.

Rohan said:

Edited - in the interests of a harmonius forum.
Keeping an open mind ...

Click to expand...

Glad to see you are learning, however the information is probably wasted on you. I suggest you should read Michelle Ann Duff's book 'Make Haste Slowly'. I found it to be very reaffirming. The write-up on the Porcupine is very interesting. The whole book is credit to him/her, it is very candid and revealing. I was amazed when I watched the Youtube video of him racing the 7R AJS against the 350 MVs etc. I would not have thought the AJS would be anywhere near them.

https://www.youtube.com/watch?v=4KJXhTCYNGg

The edit had nothing to do with motorcycles Alan.

BTW, you keep referencing all these videos, without a word of their content.
But since the relevance is not addressed, they seem to be an odd assortment of fact, fiction and sometimes just flowery language.
Perhaps you would like to rate them for accuracy of content before recommending them here ?

johnm said

[quote
I shall be at the Manx GP this year helping friends who are bringing a bike for the Classic Manx from NZ. First time for all of us except the rider. It will be interesting to see if we can get a finish!
quote]


All being well I will also attend the Classic Races at the Manx this year, so hope it will be possible to meet up with you there.

You may not be aware that Prof. Blair deliberately left something out of his book pertaining to induction tuning. By measurement on test rigs he had found that a pressure wave does not reflect from the end of the intake tube (bellmouth, radius or whatever) but at a point some distance outside the intake mouth. The actual point was difficult to determine precisely, but he settled for an extension length equal to the whole of the intake mouth diameter. He had sold the rights to his software 'Virtual Engine' to Optimum Technology by this time, but when he discussed the point at some of the tutorials he ran, those attending were highly skeptical. This 'end effect' as it has come to be known, is fully catered for in the EngMod4T software I mentioned in an earlier post.
Not often appreciated, but those who have taken the trouble to get the length of the induction system to work in harmony with the rest of the engine have sometimes been quite surprised at how it can benefit the overall performance

I took some time reading through the posts you indicated - very interesting. The PW3 you mention is quite well regarded by many racers, especially those running Commando derivatives, but you are the first person I know who uses one successfully in a 500 Dominator engine.

I've often wondered about the effect of induction length on performance. I feel that it must work in concert with the exhaust length and present an optimum torque at certain revs. The optimum length of a piston port two stroke inlet tract is radically different to a four stroke pulling similar revs. I think that the length of the MK2 Amals on my Norton engine is a result of 'suck it and see', not calculation.

Alan
the end effect is present whether it be two or four stroke. One would hardly be concerned about it in the normal way of tuning, but when using a simulator to help with a setup, the end effect has to be applied, otherwise the calculations for the intake side will not come close to matching the real life situation. Sometimes the intake can be optimised to match the tuning of the exhaust, and most often the result will be an impressive horsepower peak, combined with a very noticeable, and often unwanted falloff of power somewhere in the lower engine speed range. An alternative arrangement is to create a deliberate miss match, so that the peak power is somewhat reduced, but the loss lower down is minimised. Where an engine has a broad speed range, the intake system can move in and out of resonance a couple of times or more as speed goes from low to peak revs, and this can result in some fluctuations in the power curve. Whatever you do, these fluctuations will appear somewhere. The ideal solution is to arrange for them to have their worst effect on the power output at some point in the speed range where their effect will be minimum for the desired use.
I believe when Bob Newby first raced the Mullarney 4 valve Manx, the results were poor to the extent that some fellow competitors openly laughed, but Bob persevered and finally found the problem to be the intake length was hopelessly amiss. Once he found the right combination he moved from zero to hero in one fell swoop.
It can be a time consuming job to eliminate these seemingly trifling details, but it's a case of the details having a way of building up to mean something worthwhile. I personally use an engine simulator because it enables me to see what otherwise is difficult to imagine, but in the end the final test is always best performed on a race track, and if the results are there, the numbers are not worth worrying about.