Was the 1961 Domi racer 500 a short stroke?

Its perhaps worth pointing out then that many race engines and a few street engines have electrically adjustable inlet tract lengths.
This has been around a long time on F1 etc race engines - the inlet tracts adjust for length, very rapidly, depending on rpm and throttle opening.
Duc street engines have had this a while too...

Don't know of any Nortons with it.
Mr Garners IoM TT racer may have it ?

It would be interesting to know if the induction tract lengths arrived at are based on calculation or results of dyno testing ? And how the two generally compare. Perhaps the computer programme was created from the dyno responses ?

acotrel said:

Perhaps the computer programme was created from the dyno responses ?

Click to expand...

And with some correlations/test inputs from the race team(s), the test riders, much road testing, and owners feedback.
Surprise, surprise..
Thats called a development program.
Or programs (plural)...

acotrel said:

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.
- - - - - - - - - -
I think that the length of the MK2 Amals on my Norton engine is a result of 'suck it and see', not calculation.

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Prof.Blair seemed to think it was only dependent on ambient air temperature and rpm.That's pretty much what Johnm is using,with excellent results.
There are short or long alternative lengths that have more or less effect,but they still resonate.They say not to exceed 1/4 radius at the bell mouth entry for best results.
At 25 degrees C,a 15" intake will work at 4,677 rpm,5,994 rpm and 8,082 rpm.
I've sometimes used 14" to 16" intake length.
You might have seen this before,but here's a demo with some dyno results http://www.emeraldm3d.com/articles/emr-adj-length-intake/ The effects are very noticable.

'At 25 degrees C,a 15" intake will work at 4,677 rpm,5,994 rpm and 8,082 rpm.
I've sometimes used 14" to 16" intake length.'

Where did those figures come from ? Is it a calculation based on the revs and the speed of sound to give multiples of the wavelength of the standing wave ? I've always viewed inlet and exhaust as resonating columns of gas effecting mass transfer. Especially with a two into one exhaust where the length of the tail pipe affects the resonance in the header pipes. I don't believe it is as simple as a consideration of gas flow on a flow bench. With my own exhaust system, I believe the weld flash on the inside where the sections join have an effect which might be a problem, and I'd rather it was not there. As far as tapering inlets are concerned, why don't they have a similar effect to that of a megaphone on an exhaust ? Both inlet and exhaust have similar standing waves in them ? Can someone please explain to me how a megaphone works ? I'm aware that a Molnar Manx with an absorption muffler has much more low down power than one with a megaphone. So I know what it does, I just don't understand how it does it.

A 1/4 inch radius at the entry end of the intake is a good starting point. For a lot more on the subject of intake entry and bell mouth's in particular, try Prof. Blair's article 'Best Bell' which appeared in the September 2006 issue of Race Engine Technology magazine. Anyone interested can get a free download of the article at the Prof. Blair and Associates website, under Free Article Downloads. There are a number of other articles available that some members may find of interest.

All too often we find ourselves backed into a corner by lack of space that prevents the installation of an optimum length intake. The article detailing work on varying induction lengths carried out by Dave Walker was extremely interesting, but he could not accurately replicate on his flow bench what he discovered testing on the dyno, because the flow bench only uses one way air flow, so has no end effect, whereas the pulsating flow of a running engines system does. The Duratec photo's ideally illustrates the installation problem .

But all this is a long way from the original topic. Perhaps it calls for a new topic to be raised to continue the discussion ?

Snotzo said:

A 1/4 inch radius at the entry end of the intake is a good starting point. For a lot more on the subject of intake entry and bell mouth's in particular, try Prof. Blair's article 'Best Bell' which appeared in the September 2006 issue of Race Engine Technology magazine. Anyone interested can get a free download of the article at the Prof. Blair and Associates website, under Free Article Downloads. There are a number of other articles available that some members may find of interest.

All too often we find ourselves backed into a corner by lack of space that prevents the installation of an optimum length intake. The article detailing work on varying induction lengths carried out by Dave Walker was extremely interesting, but he could not accurately replicate on his flow bench what he discovered testing on the dyno, because the flow bench only uses one way air flow, so has no end effect, whereas the pulsating flow of a running engines system does. The Duratec photo's ideally illustrates the installation problem .

But all this is a long way from the original topic. Perhaps it calls for a new topic to be raised to continue the discussion ?

Click to expand...

yes it does, and please don't stop now

Several years ago I posted a plot on the britbike website for inlet tuning lenghts.

This is the link

http://www.britbike.com/forums/ubbthrea ... 898&page=1

This is is a graph plotting rpm versus inlet tract length using empirical formula from Blair and Vizard for 2nd 3rd 4 th node etc. . Blair figures comes from the empirical formula in the chapter in his book and Vizard via Panics Amal carb tuning books. What you can see is that the 3rd 4 th etc nodes plot on top each other for the formula of both authors. The 2nd node doesnt. Which either means there is a blunder in the calcualtion that I couldnt find or that they got different results. Frankly I think there is a blunder somewhere and I would use the Blair graph for the 2nd node.

A few things to say.

Im a bit surprised now what Snotzo said about Blairs end effect becasue i found this graph predicted dyno results very accurately.

Secondly if you dig back into the literature you will find very similar figures published by Gordon Jennings.

Thirdly yes! The ideal length wouldnt fit on my bike. I have a slimline featherbed frame and the max lenght I could fit was 12.8 inches. Theory said I needed about 15 inches. A wideline frame might be better.

I found that inlet tuning was the second easiest way to find hp and improve the shape of the hp curve on my Dommie. (The easiest was to use methanol )

I used Blairs Best Bell paper to shape my bellmouth.

Somewhere I have a back to back dyno run example which I shall try to find.


Found it

http://i168.photobucket.com/albums/u167 ... ir_Pag.jpg

This figure is of two dyno runs ten minutes apart. The only thing that was changed was to extend the lenght of the inlet tract by two inches. no jetting or ay other changes were made.

The labels refer to the inlet and exhaust tuning peaks calculated using Blair software for the inlet, cam, exhaust system. My reading suggests very similar estimates would be determined from the information in G Bells book or Panics note

This is a race bike with a megaphone system and would be no good for the street. The bike is a 500 twin running on pump petrol, CR 10.25 to 1.

johnm said:

I found that inlet tuning was the second easiest way to find hp and improve the shape of the hp curve on my Dommie. (The easiest was to use methanol

Click to expand...

Got a graph of switching from petrol to methanol - all other things being equal ?

10:25:1 on pump petrol must be about pushing the limit ?
Can't recall, do your pistons have small mountains on the top...

This post contains aspects of of what has become a twin discussion, so first, the 500 Domiracer.

I have a good friend whose uncle is probably the only surviving member of Joe Craig's team at Nortons, and was there when Doug Hele was developing the Domiracer.
He apparently is a bit of a recluse now, but I have asked my friend to contact his uncle and see if he will talk to me about aspects of the Domiracer development. It's a long shot I'll admit, but it might come off, and hopefully the uncle will be able to recall enough for me to make an interesting addition to this topic at some later date.

Now the induction discussion.
I searched through my emails to try and find the one in which Prof. Blair told me about the end effect, but can't find it anywhere. I found a later one from his associate Charlie McCartan who said the end correction added to the intake length is equal to half of the stipulated bell mouth diameter. There is an explanation of end effect by Neels van Niekerk ( owner of the EngMod4T software) which shows pictorially exactly where and how this is applied - but bear in mind, this is only for the input of data into a simulator so that the correct reflective point is used for calculations purposes.
Testing on the dyno, or racing on a track, the result of changes may be evaluated, but whatever way the results go, the real detail behind those results will be difficult to understand. A 1D simulator may not be the full answer by any means, but it is certainly an invaluable aid to obtaining an insight into what is happening with the pressure wave fluctuations occurring within the engine ducts. It makes the overlap period and how events ought to be arranged for best power output so much easier to understand.
Having read through Johnm's earlier posts and seen the dyno graph of his engine with the unusual power 'hump' around 4000 rpm, it intrigues me that such a large power boost over a relatively short period is there at all. There is most certainly a reason involving gas dynamics behind such an increase, and that reason would make an interesting exercise to discover .

I would have thought the taper on the bell mouth would increase the effective RPM range over which the standing wave works. However the effect of a megaphone exhaust seems to be to make the wave effect stronger and harsher. The 'cam spot' is magnified.

Snotzo said:

This post contains aspects of of what has become a twin discussion, so first, the 500 Domiracer.

I have a good friend whose uncle is probably the only surviving member of Joe Craig's team at Nortons, and was there when Doug Hele was developing the Domiracer.
He apparently is a bit of a recluse now, but I have asked my friend to contact his uncle and see if he will talk to me about aspects of the Domiracer development. It's a long shot I'll admit, but it might come off, and hopefully the uncle will be able to recall enough for me to make an interesting addition to this topic at some later date.

Now the induction discussion.
I searched through my emails to try and find the one in which Prof. Blair told me about the end effect, but can't find it anywhere. I found a later one from his associate Charlie McCartan who said the end correction added to the intake length is equal to half of the stipulated bell mouth diameter. There is an explanation of end effect by Neels van Niekerk ( owner of the EngMod4T software) which shows pictorially exactly where and how this is applied - but bear in mind, this is only for the input of data into a simulator so that the correct reflective point is used for calculations purposes.
Testing on the dyno, or racing on a track, the result of changes may be evaluated, but whatever way the results go, the real detail behind those results will be difficult to understand. A 1D simulator may not be the full answer by any means, but it is certainly an invaluable aid to obtaining an insight into what is happening with the pressure wave fluctuations occurring within the engine ducts. It makes the overlap period and how events ought to be arranged for best power output so much easier to understand.
Having read through Johnm's earlier posts and seen the dyno graph of his engine with the unusual power 'hump' around 4000 rpm, it intrigues me that such a large power boost over a relatively short period is there at all. There is most certainly a reason involving gas dynamics behind such an increase, and that reason would make an interesting exercise to discover .

Click to expand...

It would be good to hear more about the Domiracer.

My engineering friend back in NZ is very keen for me to build the ulitimate modern version. NZ made billet cases, Fullauto head ported for a 500, one piece 90 deg? deg crank, and Jim Schmitz pistons rods etc. In a new featherbed frame. I have a very good Manx brake replica, a six speed TT box and Bob Newby clutch beltdrive etc.

Please ignore the peak at 4000. That is the bike coming out of reversion (megaphonitis). I have not yet successfully tuned this out for a megaphone exhaust. I have some excellent suggestions from John Healy on the Britbike forum but these days Im 12,000 km from home on a company posting !!

I have contacted the website you mentioned for the simulation software and will probably purchase the 4 stroke version.

Hope we meet at the Manx. The bike is a DOHC Velocette 250. The Australian Eldee 2. It will be ridden by Bill Swallow. Bill's son Chris lives down in NZ these days and has joined up with my group of friends who race out of Wellington

http://velocetteracing.wordpress.com/th ... slideshow/

Regards

John

Rohan said:

johnm said:

I found that inlet tuning was the second easiest way to find hp and improve the shape of the hp curve on my Dommie. (The easiest was to use methanol

Click to expand...

Got a graph of switching from petrol to methanol - all other things being equal ?

10:25:1 on pump petrol must be about pushing the limit ?
Can't recall, do your pistons have small mountains on the top...

Click to expand...

Hi Rohan

Sorry no back to back petrol and methanol runs

I have only tried methanol on the dyno once and the whole session was a shambles. There was a new operator and frankly he was hopeless. He was setting up the dyno with far too heavy a drum load and finally decided the bike was no good! Next weekend it ran perfectly and won several races !!!!!!!!!

What I do have is lap times. In the morning on petrol. In the afternoon on methanol. The methanol gain was clear and consistant - about 1 second per lap of the Pukekohe circuit. Tony went from 1 min 12 seconds to 1 min 11 seconds changing to methanol. Those are extremely good times for a clubmans based bike (SLS front brake !) . For example Kevin Schwantz ran 1 min 7 sec on the best Manx Ken McKintosh could give him.

Hi John, One of the guys I know in the CMCRR runs a Clubmans Dominator and recently finished off making his own crank, says its good up to 8000 now.
Your comment about the short tracks is interesting as I run a BMW 900 and it does not really get into its stride at HD, really needs more power lower down the rev range to pull out of corners. I only did one weekend at Puke and it won against a Gold Star and Dunstall Norton to my surprise and that was mainly due to its long legs down the straights. Never happened since.
Sorry for the topic deviation.
Interesting about the induction length as the BMW has bent inlet due to the carb layout so looking at raised D port heads with smaller inlet port and longer inlet manifolds. Just a bit of experimenting with whats in the shed really. :lol:

72Combat said:

One of the guys I know in the CMCRR runs a Clubmans Dominator and recently finished off making his own crank, says its good up to 8000 now.

Click to expand...

For those interested, Steve Maney has 500 short stroke cranks with a 59.6mm stroke. We ran his to 10,500 rpm without a problem. Construction is nitrided billet cheeks and light weight steel flywheel center. Really high quality stuff.

I suspect that a 75mm stroke billet crank dominator would rev safely to 10,000 RPM which is about as much as the valve gear would probably keep up with for any length of time, even with slower lift rate longer duration race cams. You would still have a fair amount of torque if you were careful with the port job. There must be an optimum which suits a lot of race circuits if you are prepared to keep re-gearing ? That late seventies Triumph Thunderbird 75mm stroke crank always sounded good to me.

Again, why would you go to a longer stroke than the stock 500 dommie. ??
Only slightly though.
Which of course means the bore has to be smaller than a stock dommie.

Re-engineering everything just for a couple of mm ???

I'm not aware of what the standard bore and stroke of the stock 500cc dominator might be. I'm surprised that it is shorter than the stock 500cc Triumph (80mm stroke). If it is close to 75mm, I wouldn't change it. So I don't think the domiracer would have been much shorter stroke. It would not make sense to do that. When the stroke of the twin gets down to around 60mm, it all becomes too difficult unless you have four valve heads and 6 speed gear box. When the original domiracer was around, most British bikes only had 4 speeds. The domiracer also had megaphones, so if it was really short stroke, it would be a pig - the results say otherwise.
I recently saw a Seeley with a short stroke 500cc Nourish Weslake engine fitted - that would be a bit exciting. (Even had separate pipes.)

Just food for thought.

With a former World Speedway champion just a few years back, during a pre season testing session, we had a data logger on his machine to record engine speeds around the track. The engine was a GM, 92 bore x 78.5 stroke. Looking at the data afterwards we were astonished to see that on the start line , with the throttle pegged wide open, waiting for the starting gate to go, the recorded engine speed was just over 13000 rpm. That amounted to a staggering mean piston speed of approx 6700 ft/m.
Before the engine speed restrictions were imposed on F1 cars, they were very high revvers, but mean piston speeds were in the region of 5900 ft/m, not up to the level of this GM engine (a single cylinder, SOHC 4 valve,methanol fueled for those not familiar with speedway racing)

This is by way of illustrating an extreme situation, but still note, the stroke of the GM engine was longer than that suggested by acotrel.
Unfortunately, we cannot indulge in such revs with a pushrod driven engine. For one thing the basic engine design to an extent does impose certain restrictions that are hard to get around, not the least of which is controlling the valves at high engine speeds.

A much more realistic approach is to use an old design yard stick that has existed for many years now, and limit the maximum usable engine speed to that which corresponds to a mean piston speed of 4000 ft/m. For the standard Dominator stroke, this works out at just under 8500 rpm. The 75 mm stroke proposed by acotrel works out at slightly less than 8250 rpm, and the Maney 59.6 mm stroke billet crank would be approx 10250 rpm.

It would seem that at the lower engine speeds, valves would be easier to control, so more aggressive valve lift designs could be possible. At the higher engine speeds more care would need to be exercised in this area. Assuming that the efficiency of the engines were pretty much identical, whether it be a short stroke, or the long stroke, perhaps the final consideration would come down to this - for a given distance traveled on a race track, the high revving engine would have ingested and burned a greater volume of air mixed with fuel than it's slower revving counterpart. In theory therefore the short stroke, higher revving engine would win the dash to the line.
Of necessity the above is somewhat over simplified, but I'm sure most will understand what is being implied.

Against the Maney short stroke, how are you going to get your long stroke engine to be competitive acotrel ?

I should have indicated the standard 500 Dominator stroke as 72.6 mm. The 500 Weslake twin (4 valves per cylinder) had a bore and stroke of 73 x 58.75, although Dave Nourish could make billet cranks to any stroke he chose, 360, 180 or 90 degree versions. The engine with separate pipes you saw could have been any one of the three. A 90 degree crank would not work well at all with a 2 into 1 exhaust system. There would be instances throughout the engine speed range where one cylinder would be more efficient than the other, but at a different part of the speed range the cylinder efficiency would be reversed. I spent some time with a Suzuki V twin trying to minimisze the effect, and although the difference between cylinder outputs was reduced, it could never be eliminated, so single pipes, although posing installation problems, became a necessity.