15 to 1 Compression on Alky

Dances with Shrapnel said:

“burns SLOWER” is not what anti-knock is about. The air-fuel mixture should burn or deflagrate rather than detonate which is a somewhat different phenomena than detonate. Yes, for a given fuel, detonation phenomena is much faster than burning (deflagrate) phenomena.

One could make the argument that a slower burning fuel would leave a motor more prone to detonation.

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Knock testing of fuels is similar to closed vessel testing of gun propellants. It is all about burning rate. The quickest burning rate is detonation. With gun propellants, there is usually very old testing equipment involved so that there is a continual history. The readout is on a CRO and the pressure rise is mapped buy a strain gauge and photographed. With fuels, the test engine has variable compression, and it is increased until the rate of pressure rise reaches the maximum. With gun propellants, the property is known as 'brisance' - It is the rate of pressure rise divided by the total time, so it is an acceleration. With 'knock rating' you are also measuring an acceleration of the flame front - but at varying compression ratios.

If you run methanol at very high compression ratios, you tend to run out of your carburettors' ability to cope. At 12 to 1 comp in a normal Amal carb, the needle jet is usually 0.120 inch and the needles have extremely quick tapers. It is sometimes necessary to reverse drill the needle jets to avoid the situation where the main jest never operate and the carbs meter off the tip of the needles. The Dell Orto carbs on two-valve Jawa speedway bikes have no needles, so midrange jetting is hopeless. The motors become 'stop and go'. For very high comp. motors on methanol, fuel injection is probably better than normal carbs.
My choice has been to stay with low compression and more ignition advance and jet to it. The difference between an uncontrolled motor on 12 to 1 with methanol compared with a correctly jetted motor on 9 to 1 with methanol, is moot.

If I wanted to really cheat, I would copy a couple Wal Phillips fuel injectors from the 1950s and use an engine management system to control the injectors and ignition timing, using methanol fuel at about 12 to 1 comp.

Back in the early 80s when the sting of long lines to get gasoline was still fresh in my mind I looked into alcohol. My brother-in-law had a saw mill and the saw dust was a by-product that had little to no value; a perfect raw material for alcohol production.

I read a lot about the production of methyl alcohol and about utilizing it as a vehicle fuel. I learned that methyl, when anhydrous, has an octane rating right around 120; exposing methyl to a humid day can lower that rating, rather quickly, but not so much to make it unusable as a motor fuel.

The material I read talked about alcohol's heat content being about half of equivalent octane rated gasoline
hence the advice for doubling (or there abouts) the jet sizes. They also suggested, to run efficiently, raising the CR to at least 14:1.

I'm sure that you alky burners are way ahead on this, but to run alcohol in a Norton I would think something north of 13:1 would be necessary to be competitive??

Best

Methanol works because of it's high latent heat of vaporisation. When you force it to evaporate in a carburettor , it takes heat from the incoming air, so the air becomes much denser. The extra oxygen then requires more fuel' to get the mixture right for combustion. So the situation compounds. It does not take much methanol to pull the carb temperature right down and the the law of diminishing returns then applies. A good fuel would be 60% toluene, 40% methanol with acetone added to get it to blend. In pre war days, benzene was used instead of toluene. The problem with doing that is you have to accurately control the composition of the mixture.
Methanol itself has a heat content (calorific value) of about 80%that of petrol. But because of it's high latent heat you use twice as much of it. Benzene and toluene are better fuels than gasoline, but you don't get the supercharging effect if you use them alone.
Methanol will make any motor go quicker. But at high comp., it gives more power because you jet bigger to get the balance right in the combustion chamber. But again - the law of diminishing returns applies.
Phil Irving said in 'tuning for speed' - 'if you run methanol rich, you still get good power'. So in Australia most of the idiots jet too rich. Irving is correct, but methanol is like petrol if you don't jet lean enough. You still get good power - but the motor is slightly more sluggish.

You don't need 13 to 1 comp., but if you have got it, that is good. But a near standard Commando on methanol is quick enough to win, as long as you have got the bike's handling right. Don't do 'point and squirt' - get on the gas extremely early in corners. My Seeley 850 is on standard comp. with methanol and I am not bullshitting - it is fast enough.

When I first started racing, we could buy BP JA and BP JB racing fuel, which were mixes of benzene, acetone and methanol - as poisonous as buggery - but extremely effective in lower comp. motors. My short-stroke 500cc Triumph engine was only on 10 to 1 comp. Using that stuff, was the fastest it ever went.
If you go high comp. in most motors, the pistons become heavier and the crowns often obstruct the flame front. Have a look at the pistons out of a 650 Triumph engine - most have coke on the side of the crown which is away from the plug. And you cannot centre-plug a Commando engine. Toluene is much safer than benzene.

acotrel said:

Methanol itself has a heat content (calorific value) of about 80%that of petrol. But because of it's high latent heat you use twice as much of it. Benzene and toluene are better fuels than gasoline, but you don't get the supercharging effect if you use them alone.

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To be clear, the energy content of methanol is not 80% that of gasoline, and you use twice as much methanol as gasoline because that is the stoichiometric A/F requirement, not because of high latent heat. Methanol has only ~ 50% the heat content of gasoline, but because it is used at an A/F ratio ~2X stronger than gasoline, in the best case scenario the end result is a power increase of ~ 10% over gasoline in a naturally aspirated engine.

http://www.smokemup.com/tech/fuels.php

acotrel said:

Knock testing of fuels is similar to closed vessel testing of gun propellants. It is all about burning rate. The quickest burning rate is detonation.

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Do some in depth reading on the distinctions between detonation and deflagration then come back. Propellants burn, some faster than others. Detonation is partially defined as release of energy above sonic velocity whereas deflagration is below sonic velocity. The characteristics of the fuel, air/fuel mixture, temperature, pressure, engine speed and a whole plethora of other things are primarily what dictate propensity to detonate.

My brother and I have both used methanol in two strokes. If you lean the mixture off too much, you usually get a seizure before you get detonation. The two-stroke on alcohol is much more extreme than a Commando on alcohol. The only time we ever got detonation was when my brother was racing the H2 Kawasaki 750 on Speedway. A plug lead popped out of a coil on the Lectrex ignition system. My brother plugged it in again and rode in the next race. One of the boxes of the ignition system had been damaged and gave a lot more advance. The detonation broke a cylinder head.

Don't work on supposition - try it. With methanol there are two things - latent heat of vaporisation which causes chemical supercharging - and use at high comp. which raises the combustion pressure and causes more fuel to be used. The needle jets in my motor on 9 to 1 comp. are 0.116 inch. If my motor was on 12 to 1 comp., the needle jets would be 0.120. The percentage difference between those two gives an indication of the potential power difference between the two compression ratios. At 12 to 1, most guys run their motors far too rich and with less ignition advance. So the power difference is minimal.

One thing I would say about using methanol in a Commando motor - the response is lovely. Most of it is probably because with methanol, it hides-up the tuning errors. I don't know how anyone can race using gasoline. You would have to be at it forever to get the best out of it. One thing our guys found in the 1950s when they raced in the UK - the Brits got their Manxes going as fast on pool petrol as our guys could on methanol. The only advantage our guys had, was they were used to the high race speeds.

Bernhard said:

That is a novel way of preventing the bolts from breaking.

Re, “Its been reliable with over 90 races on it until the Maney cylinder bolts broke.”

I would think that the lifespan has been pretty good for these, replacing them with new ones say, 80 every races or the equalvant miles should have been the norm. Also threads that are rolled rather than cut would have been better.

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The reduced shank has an additional advantage because they stretch over a wider range - that means they apply tension over a wider range and don't need as many re-torques. The threads are rolled and not cut as you suggested.

Dances with Shrapnel said:

To Jim’s question. Pertaining to gasoline (not methanol). From discussions with Norm White, he called for 12.6:1 CR with a full hemisphere combustion chamber. I recall others of the era bantering around the 12.5:1 CR as a happy max. Going much higher would certainly boost the heat load yet from first hand experience I know a Commando with iron barrel can handle a lot of heat.

With quality alloy race barrels available today I wonder if a Commando (for racing) could safely handle more than 12.5:1 CR?

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When you push it too high (13 to 1) then the piston heats up and the thin spot is always the intake valve pocket and that is where it will burn through. Making the crown thicker or taller will just make the piston heavier and add stress. As always - its a balancing act - chose broken cases and cranks because of heavier pistons and higher CR or limt CR and keep things together. 12 to one is as far as I like to go with gas and most races opt for less at around 11 to one.

jseng1 said:

When you push it too high (13 to 1) then the piston heats up and the thin spot is always the intake valve pocket and that is where it will burn through. Making the crown thicker or taller will just make the piston heavier and add stress. As always - its a balancing act - chose broken cases and cranks because of heavier pistons and higher CR or limt CR and keep things together. 12 to one is as far as I like to go with gas and most races opt for less at around 11 to one.

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Not disagreeing with you, Jim, but the only case I personally had with burn-through was in the exhaust valve pocket, where it was close enough to the back of the top ring groove that it gave way there. That was on a short stroke 750 with the original Omega pistons, but modified for bigger valves and higher CR. That's the sort of failure behind Steve and I deciding to lower the ring grooves when we developed our design with JE.

Ken

Methanol is indeed a very easy way to get a horsepower increase if the rules allow. Even without a compression increase.

on a 10.25 CR 500 Dommie we would get a 0.8 second improvement in lap time on the old Pukekohe track. Around 1 min 11 seconds.

timing was changed from 28 deg Btdc on petrol to 31.5 deg. Plus all the necessary carb jetting changes. Large fuel lines and taps must be fitted to give the more than double required flow. About 2.3 times.

Obvious disadvantage are that you need short races and big tanks or you will run out of fuel.

Plus it is very poisonous. When I worked in Kazakhstan you couldn’t get it or it was placed under Military guard because they kept drinking it thinking it was ethanol (vodka) !!!!

Methanol is poisonous, but nowhere near as bad as benzene - and leaded avgas is not too flash either. The only time you usually get methanol on yourself is when you work on the carbs. Then skin contact is the problem. Methanol oxidises in the body to formaldehyde and formic acid. Formaldehyde is a listed carcinogen, and formic acid causes brain damage. However in the amounts of methanol you come in contact with when racing, the risks are minimal - as long as you do not drink it.

johnm said:

Methanol is indeed a very easy way to get a horsepower increase if the rules allow. Even without a compression increase.

on a 10.25 CR 500 Dommie we would get a 0.8 second improvement in lap time on the old Pukekohe track. Around 1 min 11 seconds.

timing was changed from 28 deg Btdc on petrol to 31.5 deg. Plus all the necessary carb jetting changes. Large fuel lines and taps must be fitted to give the more than double required flow. About 2.3 times.

Obvious disadvantage are that you need short races and big tanks or you will run out of fuel.

Plus it is very poisonous. When I worked in Kazakhstan you couldn’t get it or it was placed under Military guard because they kept drinking it thinking it was ethanol (vodka) !!!!

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There are a lot of myths about using methanol. One is about running it rich, another is about using high compression. I've used it in Triumph 650 engines at comps as low as 7 to 1, and it still works extremely well. If you don't get it lean enough, it behaves like petrol, but nowhere near as bad. Some people raise the needles in their carbs until they get 8-stroking then lower them one notch. I go the other way - when I get the cough, I raise them one. The results can be very different. At low comps, I use petrol needles, not alcohol needles and I make my own needle jets.
For a commando motor on standard comp., my needle jet size is 0.116 inch with 6D Mikuni needles in 34mm Mk2 Amal carbs. The mains are 670 Amal.
Do they do fuel checks in all classes at road-race meetings where you are ?

acotrel said:

Do they do fuel checks in all classes at road-race meetings where you are ?

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yes. Random checks.

but I doubt anyone would cheat anyway- what is there to prove.

Two stroke MX bikes modified in the UK are being used worldwide running 16:1 at far higher revs with E95 UK pump fuel plus additive mix - they would not tell me what the additive was though.

Many like to knock the modern pump fuel, but is it really that bad these days, just how narrow is the gap to race fuel blends I wonder.

johnm said:

yes. Random checks.

but I doubt anyone would cheat anyway- what is there to prove.

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Anyone who uses methanol in a race bike when they’re not supposed to, or does not display the correct warning signs when they do, should be banned for life.

Methanol burns invisibly, so in the event of any crash they’d be putting themselves, other riders, and marshall’s in very real danger.

Anyone who does that has no place on a track.

acotrel said:

Knock testing of fuels is similar to closed vessel testing of gun propellants. It is all about burning rate. The quickest burning rate is detonation. With gun propellants, there is usually very old testing equipment involved so that there is a continual history. The readout is on a CRO and the pressure rise is mapped buy a strain gauge and photographed. With fuels, the test engine has variable compression, and it is increased until the rate of pressure rise reaches the maximum. With gun propellants, the property is known as 'brisance' - It is the rate of pressure rise divided by the total time, so it is an acceleration. With 'knock rating' you are also measuring an acceleration of the flame front - but at varying compression ratios.

Click to expand...

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