20H/25SS Oil Type & Blend Ratio

[smirnoff]

With all of the "newer" 2-stoke synthetic oils available than back in the day.....are you still using the 25:1 ratio on these classic motors?

[pops67g]

This topic has come up numerous times on this forum. There has been lots of input. I have talked to engineers that know first-hand how the manufacturers came up with the 50 to 1 numbers that two-strokes used to tout. All that garbage aside, racing puts stresses on engines that they would rarely, if ever, see. Oil is cheaper than parts!!! For many years I have run my oil mix at 8:1 and at 29 years old the crank in my 44XS still looks about new. The replacement cost of that crank when they were still being produced was over $1100.

[trident]

This topic has come up numerous times on this forum. There has been lots of input. I have talked to engineers that know first-hand how the manufacturers came up with the 50 to 1 numbers that two-strokes used to tout. All that garbage aside, racing puts stresses on engines that they would rarely, if ever, see. Oil is cheaper than parts!!! For many years I have run my oil mix at 8:1 and at 29 years old the crank in my 44XS still looks about new. The replacement cost of that crank when they were still being produced was over $1100.

Yup. I like 8:1 in anything with full complement rod bearings... That's ALL old Merc 30, 40, 44, 20, 22 and so on.

Remember, too, only the 'back end' is water cooled. The front end, the entire crank train, is cooled and lubed by incoming air, fuel and oil.

Say it with me, Oil is cheaper than parts. Oil is cheaper than parts.

[ZUL8TR]

Since these 2 cycle stockers are basically low compression engines when a CR based on the cylinder volume from TDC to top of the exhaust ports of around 6.5:1, if using 8:1 oil what fuel station octane do you use if there is supposedly a lowering (debatable) of 1/2(M + R) octane rating with oil ? I use E free fuel on the old guys.

He also asked about type of oil for the old ones. I presently use Mercury Premium Plus in my 1973 25ss deflector and the Yamato Y80 with E free 87 at 16:1 and are my same engines from the APBA 70's still with same good internals. I run them like 7000+ revs and it keeps that excess oil from carbon build up on piston, ports. There is always a flood of oil in the front end when I pull the covers.

[jeff55v]

Question:
How well would an engine run at 4:1 oil/fuel ratio?

[pops67g]

The fuel we use is dictated by rule to be ethanol free (or unoxygenated) fuel. Where I live the only octane in this type of fuel is 91. We don't really need that high of octane but it's all there is. It always passes the fuel meter so that's what we use. This fuel mix was arrived at by testing on a dyno (to the best of my knowledge), not just a wild guess.

[rumleyfips]

In the 60's and 70's I used Shell mineral based oil ( it was free ) at 20 - 1 . When I took a powerhead apart, the needles stuck to the crank and the rod came free. There was always enough oil on the reedcage to make the reeds go pop. Seemed good enough for me.

[Smitty]

50:1 and higher ratio oils were developed so that fishermen wouldn't foul plugs while trolling and so that you didn't have to scrape carbon out of the exhaust port as a part of the normal preventive maintenance of the Fifties and earlier. These oils have particular components ("bright-stock" is one) that don't work so well in rich (like 8:1) ratios, according to the chemical engineers who designed them. Don't use oil for pleasure boats, get real two-stroke racing oil, which is intended to be used at ratios like 20:1, 16:1, etc..

[ZUL8TR]

Here is a link for additional discuss but for Yamato

https://hydroracer.net/forums/forum/m...highlight=tcw3

[Yellowjacket]

Mercury tested way back when and found that the best power was obtained at 16:1.... Synthetic and better oils allow higher fuel/oil ratios, but the best power comes from better ring sealing.

If you're running much more oil that 16:1 and certainly at ratios like 8:1 you need to be looking at your jetting. Running more oil leans the fuel air ratio out and you can cook things from being too lean...

[dwhitford]

In the 1950s, Mercury recommended 3/4 pint (12 ounces) of oil for each gallon of gasoline. That's a generous 10.67:1 ratio, quite more than necessary nowadays. I suspect they were hedging their bets, and early 1950s oil wasn't as good then as it is now. But that was in an era when the pre-war and early post-war Johnrudes had factory recommendations of a pint-and-a-half (24 ounces) of oil for every gallon! I read such a recommendation right off the tank or clamp bracket of my 1st Speeditwin.

Times and oils have changed. Throughout my alky career, I ran 5% castor oil + 1% UCON synthetic at RPMs exceeding 11,500 with no problem. Castor oil was then considered to be the best high-temp lube. My oil mix was slightly richer than 16:1, but bear in mind that I was passing twice as much fuel -- hence twice as much oil -- through the engine with every piston stroke. I got my fuel recipe from Bud Wiget, a many-time alky champ, and a Cal Tech graduate who worked for Shell Oil as a lube expert. Bud also was on contract to an Indy team for several years, mixing their high-nitro qualification fuel.

Here's a side note: some of the Rossi drivers (modern-day alky drivers using the Italian engines at 14000-16000 RPM) needed to upgrade their oil concentrations substantially to prevent serious bearing failure. I don't know exactly what the new recommendations are, but I hear that they are at least half again the 6% oil that I always used as an alky driver.

I ran my service Merc (a Mark 20) back and forth to work in the 1000 Islands on 16:1 Pennzoil outboard and whatever gasoline we sold on our gas dock for two summers. I recently pulled that engine down, checked it, (all OK), and installed it on an H- Quickie tower and 16:21 gear case for ''lake-racer'' use. It'll still be OK on the ol' 16:1 oil mix, I'm sure.

If you race a Yamato, and the Yamato factory has an oil recommendation, I'd follow it. You won't ever really get much more horsepower by skimping on oil to get a skimpy bit more gasoline in the fuel mix.

[Ram4x4]

Oil is part of the fuel mixture, its volume counts in the typical stoichometric 14:1 ratio for gas engines, so the more oil, the less actual combustible gas per charge, effectively leaning the system. Hopefully everyone is tuned correctly for whatever fuel and oil ratio they use.

As for synthetics and ratios, my primary experience is with air cooled engines and to that extent, I routinely ran Amsoil mixed at 100:1 in my 2-stroke paraglider engine. 202cc, single cylinder, 28 HP. I put close 1000 hours on that engine and it never failed. Internals were in perfect shape.

That's not to say I plan to do the same on my Yamato by no means, but modern synthetics have a lot to be said for them.

[ZUL8TR]

The following is from a post I made over at Boat Racing Facts:

http://www.boatracingfacts.com/forum...il-yall-runnin

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Found this over at a motorcycle site and interesting read about how the oil in the fuel works for lube and oil ratios.

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05-24-2006 03:34 PM #1 Yamaha Tri-Moto
Location:Canada

All About 2 stroke Oil Ratios. Interesting find
I was Browsing the net and came across this, figured ive seen so much talk about oil ratios this may help some people out. I sure found it interesting.

*I did not write this, Spanky over at mx.com did*

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.


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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.


As a side note, I no longer run 26:1, I now run 32:1. I'm not a young man any more, and I just can't push as hard as I used to, so I don't need as much oil now. 32:1 is enough oil to do what is needed for me now, since I'm getting slow...

[Smitty]

As an object lesson in why the type of 2-stroke oil used might be more important than the mixing ratio, here's a story I heard from the instructor of the OMC Outboard Service School 1 class I went through many decades ago:

It seems that the U.S. military was having a lot of engine failures in the Evinrudes they were using in the rivers in Southeast Asia during the Vietnam War. This was with models that were giving fine service everywhere else. As I recall the story, whoever was in charge of the (outboard) motor pool there had been using, per orders, the military's own 2-stroke oil, in olive-drab cans, for which the spec had probably been developed in the Thirties or before. Having noted the evidence on the piston skirts of some engines he had torn down, this guy went into town (Saigon? Bangkok?) to the only civilian OMC dealer, and bought his entire stock of Evinrude-branded oil. Back at the base, he dumped out the mil-spec oil behind the shop, and refilled those cans with Evinrude oil. And had no further engine trouble.

[Smitty]

Another thought:

Everybody here, every racer of 2-strokes, eventually gets asked by a neighbor or friend about how to mix oil for an old "antique" 2-stroke, the question being, should I mix according to the instructions on my new can of 50:1 oil, or should I go by the mixing ratio called for by the manufacturer of the motor back in the Fifties? Now, if you were to write the company that makes the oil, they would say go with the engine manufacturer's recommendations, but if you can still write the makers of the old engine, THEY would say to follow the oil maker's mixing ratio. Why? Because the lawyers in each company want any legal responsibility for the old engine shifted to the other guys. Ah, lawyers . . .

My answer to this question is that the very oil-rich mixing ratios called for in the decades of "Bunker C" oils of my boyhood are not appropriate for modern oil, regardless of how old the motor is. So in my 1956 5 1/2hp Johnson (one of the sweetest trolling motors ever), I use OMC 50:1 oil. I might, repeat might, mix it a little rich, maybe 40:1 or so. But I sure won't mix it to the original 12:1 or 16:1 or whatever it was in 1956 (I don't know and don't care). With that 5 1/2 and a couple of bigger ancient fishing and pleasure boat motors I own, I get good results this way.

But if I were running and equally old stock RACE motor like a 20H, or some other old 2-stroke that runs flat-out (my 1952 Titan 40 chainsaw), instead of using the modern high-ratio oil I want modern 2-stroke racing oil (typically for motorcycles), and use it at the rich ratios for which it was designed (12 to 20:1).

Different oils and different ratios for different uses. At least, that's how I see it.

[ZUL8TR]

Exactly what was stated in the piece I posted above your 1st post. Trolling and average service use less oil, high sustained rpm more oil. It's all about residual oil in the 2 cycle engine; less rpm less residual needed, more rpm more residual needed.

[Smitty]

Yup, good (I didn't write it to answer you or anyone in particular).