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Thread: My Kilo Motor

  1. #71
    Team Member genea01's Avatar
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    Default oil

    there was a test in the motorcross world were a mech tested a 50:1 to 32:1 and 24:1 and the 24:1 made more hp on the dyno and he said it was compression related and ring seal you can research back or google about 2 years ago and you should find it, they had the story in there magazine.

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    One guy I know in OZ who used to build and race (350's kneelers I think)
    Used to practise from the reliable mix ( had cockpit adjustable main jets)
    to lean and how far it would go before meltdown.
    He said it was always worth a few postions if you were not leading
    He said engine went from 18,000 to 24,000.
    If it didnt make more power it wouldnt rev up would it?
    They practised the distance so the driver knew when he could lean it out.
    We must have all been in an outboard when it is running out of fuel..what does it do...revs up some more
    For how long is the question.

    I think the more oil and ring seal issue would be particular to each engine?
    I guess you need to plug one into the 'spinatron'

    Is it Jennings book or Bells where he leans the oil down till he sees scuffing then adds it back to find the right ratio. I guess this would be fuel, oil, engine etc dependant?

    So when you run an E-tec on xd100 and re set the computer it makes less horespower?

    The only recent test data I have read on fuels was in Hotrod and a chev.
    a 9.5:1 carby engine and they ran it on high and low pump gas, av gas and some VP product.
    The Vp guy promised them it would make most power on the VP and he was right.
    He explained that even though the engine had low compression the race gas burnt faster etc( timing was set for each fuel) and hence also produced the best BSFC.
    The av gas is not designed to do that so it didnt have the same improvement he explained.
    Avgas will certainly stop detonation as thats what its designed to do, I guess knowing how it does that could be interesting.

    Fuel density, specific gravity, btu's, bsfc, imep, egt all good stuff for a good thread.

    I wonder what the last GP500 race bikes ran on?
    You never see any smoke either.
    The Japs seem to keep data on those very close to their chests as I can find very little info on them as I assume they would be the last big budget 2 stroke development, were they?

    Avgas is also full of lead, I wonder if that is effecting anything?

  3. #73
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    What I think Fred meant to say was " in competition engines lean doesn't increase power" as they're running as lean as they dare.

    I have no doubt that in motors that are not running on the edge of heat distress a jet size smaller often helps, but as the fuel/air is a major contributor to piston cooling, running lean without piston ceramicing can cause nasty problems.

    the fuel question is so dependant on what your running & which hull, where & how, you will get a different answer from everybody that comments.

    I do like Avgas it seems to smooth my motors out, but prefer the higher heat output from pump gas, as the more heat the more pressure on my pistons.
    That's one of the reasons I like plenty of oil in the mix better heat transfer from the piston through the cylinder walls, leading to slightly cooler & more dense crankcase contents giving a lower energy loss from crankcase compression.

    Two-stroke high performance engine design & tuning by Cesare Bossaglia is a good read, almost as good as Jennings but slightly different but expensive & not available on the web

  4. #74
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    Can extra oil compensate for a lean fuel mix and vice versa?

    I wonder if the E -tec alter the fueling when you change to 100:1?

    I wonder what the oil ratio to power, graph looks like?
    Is 1% to 2% a small difference compared to 2% to 4% power wise?

    Why does extra oil make more power, it cant be adding to the explosion so....

    Helping to seal the exhaust port to piston seal?
    Does that mean the M31 will produce less power increase with more oil than a MOD 50?

    Is it ring seal...so thats why OMC consumer engines have pressure back rings and their race engines dont coz they run double oil?

    Graham Bell, Two Stroke Performance Tuning
    available from here;
    www.bevenyoung.com.au

    Its a few years newer than the Jennings book
    Has half a chapter on fuel and oil, much more then Jennings

    PS If synthetic oil is any good shouldn't it produce the same power using less than the other oils?
    Graham Bell says he could always produce more power with Castrol R ( avgas in all test)
    I guess this is 80's test data?

    Found this http://www.bridgestonemotorcycle.com...oilpremix6.pdf
    Jennings from 78

  5. #75
    Sam Cullis Mark75H's Avatar
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    Quote Originally Posted by Powerabout View Post
    Ignoring viscosity issues does the following add up?

    lets say you have gone from 50:1 to 25:1, (2% to 4%)
    Therefore you have lost 2% of the fuel as it is now oil.
    That assumes the oil has absolutely no fuel energy ... which is wrong. In general, lubricating oil (synthetic, mineral and vegetable) has about the same fuel energy per weight and volume as gasoline.


    The question about oil ratio and power is a piston/ring & cylinder seal improvement ... more seal, more pressure = more power ... pretty simple
    Since 1925, about 150 different racing outboards have been made.


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    Mark 75

    Power in the oil, I hadnt thought of that, makes sense.
    So that adds to the story, how many BTU's are in each of the oil brands we use?
    Does that means there is a 50 50 issue with dino oil more btu but synthetic less friction and better sealing?
    and will the oil help or hinder detonation?
    ( assuming the synthetic cleans the engine via detergent process rather than a combustion process?)

    too many questions

    Cheers

  7. #77
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    That's a very interesting point, has anyone seen any figures or creditable paperwork on this area.

    What percentage of the semi particulate oil vapourises & joins the fuel & what stays as a condensate & does it's job as a lubricant? Some of it's got to burn or they wouldn't tell us it was low ash but a significant percentage must condense & assist the ring seal & to make such a mess in the exhaust.

    With regard to the 55H power increases, almost 10% seems a huge jump.

    This side of the Atlantic we see very few of the competition Mercs, so I have little knowlege of them, is 40hp the power output of a real good one, a OK one or a tired old one with slack rings?

  8. #78
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    lifted from www.motorcross.com



    Pre-mix 101

    OK, looks like it's time for a little pre-mix 101. I don't usually get into ratio discussions, because mix ratios are like religions to most people, and they tend to be closed-minded on the subject, but I'll put in my $.02 here anyway.

    There is a prevailing myth that less oil is better, and that the oil in the fuel is what lubricates the engine. Both are wrong.

    *less oil is better* People think that if they have a plug fouling problem or a lot of spooge, they need to run less oil. Wrong! Both problems are caused by rich jetting, and have nothing to do with the mix ratio.

    *the oil in the fuel is what lubricates the engine* The engine is lubricated by the residual oil that builds up in the crankcase. All the oil in the fuel does is replenish this oil.

    The best way to determine if you are running enough oil is to check the level of the residual oil in the crankcase. If the ratio you run leaves enough residual oil in the crankcase to cover about 1/8" of the bottom of the crank wheels, then you are fine. If you don't have that much residual oil in your crankcase when you pull the top-end off, you aren't running enough oil for your riding style and conditions.

    With that said, to have that amount of residual oil in the crankcase at 50:1 (a ratio made popular by magazines and oil bottles), you can't be riding very hard, or your bike is jetted richer than necessary simply to deliver enough oil. I arrived at 26:1 for my bike with my riding style because that is the amount that gives me the proper amount of residual build-up. Small-bore engines require greater oil concentrations than larger engines to achieve the proper amount of residual build-up, because they rev higher and have higher intake velocities. Along the same lines, someone that pushes the engine harder, and keeps the revs higher, also needs to use higher oil concentrations to achieve the proper residual build-up.

    To understand why the residual oil is so important, you have to understand what happens to the oil in your fuel when it goes into the engine. While the oil is still suspended in the liquid gasoline, it can not lubricate anything. It has about as much lubricity at that point as straight gasoline. When the gasoline enters the engine, it evaporates, dropping the oil out of suspension. Now that the oil is free, it can lubricate the engine, but it must get to the parts to lubricate them. The way it gets to the bearings and onto the cylinder is by being thrown around as a mist by the spinning crankshaft, and the droplets are distributed by the air currents moving through the engine. Ever wonder why there are two small holes in the transfer port area of the crankcase, right over the main bearings? These are to allow some of the oil droplets being flung around inside the engine to drip down into the main bearing area.

    Some of the oil eventually makes it into the combustion chamber, where it is either burned, or passes out the exhaust. If the combustion chamber temps are too low, such as in an engine that is jetted too rich, the oil doesn't burn completely. Instead, some of it hardens into deposits in the combustion chamber, on the piston, and on the power valve assembly. The rest becomes the dreaded "spooge". The key to all of this working in harmony is to jet the bike lean enough to achieve a high enough combustion chamber temperature to burn the oil, but also still be able to supply enough oil to protect the engine. If you use enough oil, you can jet the bike at it's optimum without starving the engine of oil, and have excellent power, with minimal deposits and spooge. At 50:1, you simply can't jet very lean without risking a seized engine due to oil starvation, unless you're just putt-putting around on trails without putting the engine under much load.

    With the high oil concentrations that I use, I tend to get far more life from my cranks and rings than most of my friends that run leaner oil ratios. The high oil content also produces better ring sealing, so more of the combustion pressure is retained.

    One small point. No one ever broke an engine by using too much oil.


    Pre-mix ratios and power production

    I have run Dyno tests on this subject. We used a Dynojet dynamometer, and used a fresh, broken in top-end for each test. We used specially calibrated jets to ensure the fuel flow was identical with each different ratio, and warmed the engine at 3000 rpm for 3 minutes before each run. Our tests were performed in the rpm range of 2500 to 9000 rpm, with the power peak of our test bike (a modifed '86 YZ 250, mine) occuring at 8750 rpm. We tested at 76 degrees F, at 65% relative humidity. We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1. Any more oil than that, and the engine ran poorly, because we didn't have any jets rich enough to compensate for that much oil in the fuel, and the burn-characteristics of the fuel with that much oil tended to be poor. The power loss from 18:1 to 32:1 was approximately 2 percent. The loss from 18:1 to 50:1 was nearly 9 percent. On a modern 250, that can be as much as 4 horsepower. The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall.

    Now, I realize that 18:1 is impractical unless you ride your engine all-out, keeping it pinned at all times. But running reasonable ratios no less than 32:1 will produce more power, and give your engine better protection, thus making it perform better for longer.

  9. #79
    Sam Cullis Mark75H's Avatar
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    Pretty good, except I would give credit to outboard mfgr's operating instructions for promoting 50:1 ... a tidbit that would add to his overall good understanding.


    There might be a correlation between motor size and the load of oil they will tolerate and he may be right about velocity thru the system being the key. Merc recommended 18:1 for all the racing motors from the V-6's on down; Hot Rods were famous for using even more ... but then again they were using the crankshaft rotary valve set up that probably needed extra oil to help seal it.


    On 2 strokes oil lubricates rings and piston skirts mostly from the sides and bottoms, you don't need to worry about oil lubing from the top after combustion. On a 4 stroke unless you add oil to the fuel as "top oil" they get no top end lube at all and can run for tens of thousands of hours with no problem.

    Synthetics don't have cleaning detergents, they are just cleaner and more pure. Dino oil only has the worst junk removed from it, it is still a mixture of "stuff" when used as 2 stroke oil ... synthetics are chemically built up from alcohols and only contain the chemicals the makers want in them.

    There are a lot of things regarding the octane & combustion related to oil, I'll post more later
    Since 1925, about 150 different racing outboards have been made.


  10. #80
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    Default More oil and Avgas

    Howdy y'all.

    Sorry to have missed the fun this week. Lots of work and too little time. Also, for some reason I'm not getting bounce-back email from BRF! Hmmm. better complain to the management!

    Anyway, it's great to see such lively, informed discussion. You've all identified the answer(s) before I could reply. Sealing the piston rings is very important, but don't forget the reeds and inter-cylinder labyrinth seals. These close clearance "seals" all perform better when well lubed.

    The referenced MK55H dyno test proved opposite what stock drivers told me in the 1970's - it was a relief to see conclusive data for myself many years later. While on the subject of beach racing, another popular tip was to undercut the inter-cylinder seals to keep the crank from dragging. I'd like to know see the data where that actually helps. Lemme see: increased clearance = decreased crankcase pressures due to internal leakage and a somewhat undersupported crank. What part of this makes sense?

    The oil "river" discussed is critcal to engine life as well. As a young Mercury mechanic, I was taught to run race engines with as much oil a possible without fouling the plugs off the beach - the engines last longer. And somewhere along the line it was explained that there is more heat energy in oil, hence more oil more power. The only reason to run less oil was to reduce smoke and improve resistance to fouling (for fishing engines). Most likely the thin ration were developed for sales & marketing bragging rights about the least cost-to-operate engine.

    Now for fuel choice. Oxygenated racing fuels will deliver more power than Avgas - for a while. Most degrade rapidly once the sealed containers are opened and misbehave accordingly. The same goes for any pump gas (Turbo Blue, etc). One "pump" gas exception is Avgas. Spec's call for two year stability in an opened container (such as an aircraft fuel tank). After losing a few heats traced to spoiled (canned) racing gas and (pump) Sunoco 260, I switched to Avgas. You can buy it anywhere, trust it to deliver consistent behavior, and never blow the meter even when it's hot. The rule of thumb is to tune for the fuel you run, don't make any changes, and go have fun racing. Sadly, it's taken me several boxes-o-pistons worth of experience over thirty-some years to arrive at what works consistently.

    There's my 2-cents worth. Great thread!

    Tim

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