Dyno questions

L.A.B.

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acotrel said:
I still can't remember whether the idle screws adjust fuel or air.
The Concentric Mk1 pilot air screws (referring to them as idle screws may lead to some confusion with the throttle stop screws) adjusts AIR.

Screwing the pilot air screw INWARDS richens the idle mixture.

 
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Can't say I've ever seen a concentric with adjustment screws for BOTH fuel and air supplies ????
That is what it is showing, is it not ?
 
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Rohan,
What you are seeing there is a modification to allow for cleaning the idle pilot on the backside, as it was originally part of the casting. This mod required you to drill and tap to the same thread pitch for the idle screw. Modify an old air mixture screw by cutting off the tapered part and screw it into the other side. If there was a blockage then it could easily be dealt with by removing the screw and blowing it out or cleaning any grunge or particles behind the pilot jet as it was a press in fit. I use a bit of RTV sealant after installing this setup as well as an o-ring to make sure it stays put but is easily removable if it is necessary. you will find it here: http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html
Cheers,
Thomas
CNN
 
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+1 to the above. It is such a useful mod that the new Concentrics come already fitted this way.

Glen
 
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The je'tting chart on the bushman's site is interesting. It mentions 'straight diameter' effectiveness. I suggest the needle diameters for both Mk2 Amals, and VM Mikunis are identical at 3 mm, so the multi-varied taper Mikuni needles can be used in Amal carbs of similar sizes to Mikunis.
 
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CanukNortonNut said:
Rohan,
What you are seeing there is a modification to allow for cleaning the idle pilot on the backside, as it was originally part of the casting.
Thought we should make it clear that this is not the average old Amal that is shown in cutaway form there......
 
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Re dyno testing with methanol
Speedway engines have run on methanol for years. The engine builder responsible for most of the top riders engines (including those used by Ty Woffenden, current world championship points leader) regularly tests his motors on a fully instrumented Schenk eddy current dynamometer, directly connected via a crankshaft coupling. Despite certain restrictions, such as 34mm choke size and a mandatory exhaust system, maximum measured power is in excess of 80 bhp in the best motors, and this output is obtained with the air fuel mixture being leaner than most riders will use when actually racing. Note that this is as tested on the dyno - on the track conditions may be such that major changes in several areas will be required in order to optimise traction and drive. For those interested, these engines (GM in particular) have been data logged for start line rpm, and figures in excess of 13000 have been recorded. Did someone once say methanol was supposed to be slow burning?
 
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Snotzo said:
Did someone once say methanol was supposed to be slow burning?
Slow burning is a relative term ?
As in not exploding as its leaned off or compressed, a lot.

I have a little aero engine that was recorded as making peak power somewhere up near 24,000 rpm.
Methanol /nitromethane /castor fuel mix, but only a low % nitro.
So slow burning is a relative term.

Interesting stuff.
I eyed off one of those GM engines, well used, a while back.
They come in different varieties, think it was 4 valve sohc.
Cheap serious hp. ?
Not a simple conversion for road use though, needing an oil circulation system and being weened off the alcohol.
So the compression has to be backed off, considerably.
 
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Dances with Shrapnel said:
Holmeslice said:
The DWS 1007cc Seeley puts out some mighty impressive numbers.

But, who really cares about the number? It's all relative.

Example:

My last session, my own race bike put out about 29hp at the rear wheel
I'm quite happy about that, because the time before, it put out 28.

See you all in turn 1
What Holmeslice does not say is that it also puts out barrel loads of torque. As a friend used to say about Mack diesel trucks; "not much on revs but can haul 98 ton of rock".

I think Holmeslice is right in acotrel's camp on this torque thing. :D
I don't care how much torque it makes 29hp isn't getting you anywhere in a race.
 
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Forgive me for coming into this late, but:-

texasSlick said:
At the university where I once thought, we had several test bed engines fully instrumented. These had pressure transducers in the heads so we could get a pressure signature. Right after ignition, pressure spikes rapidly, then after the piston starts down the power stroke, the pressure falls nearly as rapidly due to the increasing cylinder volume as the piston moves down the cylinder. Now consider a Diesel engine...we all know they are torque'ers. They get the torque by the injectors continually pushing fuel into the cylinder, even as the piston is moving down the power stroke. This addition of fuel, when burned, keeps the pressure from falling off as rapidly as that of the gas engine...hence more torque.
You can't burn any more fuel than the air you have drawn into the cylinder will allow you to. If more gasoline could be burned in an engine why not just enrich the mixture? I don't think diesels make more torque by finding more free oxygen.

It was my understanding that diesels are primarily more fuel efficient, because they are able to operate at higher temperatures than a gasoline burning engine; there is less heat lost to the walls of the combustion chamber. I suppose the pressure in the cylinder reaches a higher peak and remains high longer because less heat is lost to cylinder walls. So higher combustion pressure, sustained longer, results in more torque but the heavy duty nature of the components tends to limit engine speed and so horsepower is not increased proportionately.

texasSlick said:
Now the slow burn rate of methanol, mimics the Diesel effect....the fuel burns slowly, producing less of a peak pressure, but sustains the pressure longer than petrol, producing more torque.

Finally, it seems to me that peak horsepower on methanol is less than petrol, because of the lower energy content, and also because at top RPM, the slower burn rate means fuel is blown out the exhaust before optimally completing the burn.
Years ago I was told that the Vintage Racing Motor Cycle Club (VRMCC) in the UK allowed the use of methanol so that production based bikes with cast iron cylinders (and maybe heads) (e.g. BSA B33) could compete against all alloy period race bikes (e.g. BSA Gold Star). In some respects the B33 had the potential to be more efficient/powerful than the Goldy, less heat/energy being lost through its iron cylinder and head, but too much of a good thing would result in the fuel/air charge being heated to the point of detonation. A freshly inducted methanol mixture would be cooler for a given cylinder and head temperature. So the methanol itself did not produce more torque or power, but it allowed the engine to operate in a state of tune that would.
 
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There is also the minor matter that diesels typically operate at around 18:1 compression ( and gulp unlimited air.).
And methanol burners make their best power at approx 14:1
If petrol engines could operate with this much compression, they too would be so much more efficient.

Diesel engines have come a long way over the years.
Audi, Peugeot, BMW and Benz all have some very strong diesel passenger car engines.
Its the top of the range for some of them.
And Audi won the LeMans 24 hr a few years back with a diesel, although it had some sort of dispensation to compete against the petrol cars ?
It was something like 800 hp (?).

Prewar, racing fuel was a blend of something that was a considerable advantage over petrol - prior to methanol becoming available.
Anyone remember/know what it was ? xxxxx/benzol ??
Its in the old handbooks, but I'm not able to look it up just now.
Essential for all-iron engines to survive when ridden hard ?
 
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Rohan said:
There is also the minor matter that diesels typically operate at around 18:1 compression ( and gulp unlimited air.).
And methanol burners make their best power at approx 14:1
If petrol engines could operate with this much compression, they too would be so much more efficient.

Diesel engines have come a long way over the years.
Audi, Peugeot, BMW and Benz all have some very strong diesel passenger car engines.
Its the top of the range for some of them.
And Audi won the LeMans 24 hr a few years back with a diesel, although it had some sort of dispensation to compete against the petrol cars ?
It was something like 800 hp (?).

Prewar, racing fuel was a blend of something that was a considerable advantage over petrol - prior to methanol becoming available.
Anyone remember/know what it was ? xxxxx/benzol ??
Its in the old handbooks, but I'm not able to look it up just now.
Essential for all-iron engines to survive when ridden hard ?
I remember my old man saying he used to use a mix of petrol / benzole if he removed the compression plate from his Velo KSS pre-war, but in what proportions I don't know, but it was seen as being the business in those days. Benzole was used 90% mixed with avgas for the Schneider Trophy winning Rolls Royce R powered seaplane and subsequently included tetra-ethyl lead, methanol and acetone - a real noxious cocktail. Some classic racers used to throw in a dollop of acetone into the mix.
 
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With a blend of 60% methenol, 40 % benzene ans a bit of acetone as blending agent, you get the best of both worlds. The high latent heat of vaporisation of methanol gives a colder charge, inducing more mixture, it also has unlimited antiknock. The benzene has a higher calorific value. The mix used to be used in the 40s by Maserati. Benzene is too poisonous to be used that way these days.Over to you, Rohan !
 
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acotrel said:
Benzene is too poisonous to be used that way these days.Over to you, Rohan !
Benzene is still a component of modern fuels ?

Isn't that where the concern over fuel station operators getting leukemia is coming from ?
 
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Benzene is not intentionally added to modern fuels, however it is usually there in small amounts. Toluene is a much safer option as a fuel to be blended with methanol.
 
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30% methyl-benzine worked OK for me about 30 years ago,with high-compression pistons.I think it becomes hard to start up with any higher percentage.
 
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Toluene has similar chemistry to benzene without the level of toxicity, and it is relatively cheap. The reason that benzene was ever blended with methanol and acetone in BP JA and JB racing fuels was to provide calories (energy). Methanol provides about 0.8 times the energy of petrol, but you use it about twice as quickly when it is on its own. You don't need 100% methanol to get the benefit from its high latent heat of vaporisation. About 60% will achieve the same result, however if a high calorific value aromatic hydrocarbon is entrained with it, the overall result is better. I used both BP JA and JB in the 60s, and that was the best my short stroke 500cc Triumph engine ever ran. The comp ratio was about 10 to one, you don't need 100% methanol for that. I used 12 to one pistons, head, barrel, cases from a 650 Triumph with a 63 mm stroke crank, and ridiculous cams. It was a totally top end motor and a bastard to ride with only a 4 speed CR gearbox. But with BP JA fuel and a two into one exhaust, it was magic as long as you kept your nerve.
Incidentally, at one time that fuel went through the bottom of my fibreglass tank, it was all over the motor and myself. I shudder to think about it.
One thing I should say about fuels, is to never mix nitromethane with a hydrocarbon fuel (methanol blend or otherwise), it is very dangerous.
 
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acotrel said:
Methanol provides about 0.8 times the energy of petrol, but you use it about twice as quickly when it is on its own. .
Methanol has almost exactly about half the energy of common gasoline/petrol, so you use about twice as much of it.

You keep misquoting these numbers - even though we have had this discussion before.
THIS IS QUOTED, CORRECTLY, ALL OVER THE PLACE - seek and read...
e.g. http://physics.info/energy-chemical/

acotrel said:
One thing I should say about fuels, is to never mix nitromethane with a hydrocarbon fuel (methanol blend or otherwise), it is very dangerous.
You can buy methanol blended with nitromethane in cans, ready to use in miniature aero engines.
Up to quite high % of nitromethane, if your engine needs/will stand it.
With normal precautions, it is as safe as any fuel ?
Don't talk rubbish ?
 
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Rohan, The following table lists the g ross calorific values of many fuels. Ethanol is similar to me thanol in calorific value. I said that methanol has 80% of the calorific value of petrol, and I meant it:

http://www.engineeringtoolbox.com/fuels ... d_169.html

As far as nitromethane is concerned, it is quite safe to blend it with methanol. Methanol is not a hydrocarbon. If you mix it with petrol you can get a reaction which can lead to combustion in the tank. Our speedway guys used to flush their fuel systems with petrol after using nitro, and one guy ended up fighting a fire in his Vincent outfit on the way home from a meeting. Nitro is not safe. 'A little knowledge is dangerous'.On one forum there was an idiot who claimed it burns slowly if you set fire to it. Nitro compounds usually have a critical height . They burn slowly at first however the acceleration is not linear. If you filled a two metre plastic pipe with nitro and stood it upright and set fire to the end, you would probably get an explosion as the fire accelerates. In explosives factories, most fatal accidents occur at t he burning ground due to this factor. If you stack gun propellant too high, then set fire to it , it burns slowly at first then accelerates to a whoosh, if you are lucky. However a bloody big bang, if you are not.
 
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