Fuel viscosity change with increased oil ratio

[Master Oil Racing Team]

You are right about ambient pressure Sam. I was thinking of capped off vessels. Master Oil viscosity changes dramatically with temperature change because there were no additives to keep it in a certain range. The additives were basically for extreme pressure and temperature. I don't remember exactly but it might be like 5 in the middle of a heat wave in August in Texas and 25 in a cold winter. But then it's lubricity reduces surface tension, So your mention of Klotz not recommending its product for oil injection systems due to viscosity, got me thinking. In it's early day petroleum based oils could not match the lubricity of Master Oil. But since then, synthetics have come on the market and are superior. This is what I'm wondering. Take two oils with the same viscosity. One standard petroleum base. The other a premium synthetic oil. Would there be enough lubricity difference with the synthetic to cause enough reduction in the surface tension of the gasoline to make a measurable difference?

[Mark75H]

Again, this is something well outside the original test question, but probably can be addressed with the same apparatus.

I want to show whether you have to change carb jetting if you use more oil because the increased oil slows down fuel flow thru carb jets when you make an oil mixture change within normal oil ratios used on 2 stroke motors ... Specifically 50:1, 24:1 and 18:1


PS: I don't think gas has any surface tension to speak of ... It does't stand as a bubble when you put a single drop on a plate. It runs out flat.

[Mark Poole]

Is this test going to be simply pumping/pushing the fuel through the 030 passage?
Just thinking.......might see more of a difference if the test actually flowed air through a carb and made the venturi "pull" the fuel through the jet and up the high speed nozzle.This way the mixture has to fight gravity as well as flow due to the effects of the venturi. Interested in the results either way.

[Mark75H]

It might be different, but would involve building and running a rather dangerous apparatus that I am not interested in building and operating. It would take a lot more gages and adjusters to run consistently.

The gas and gas oil mixture will just flow out the bottom of the burette by gravity; being run by the same height of liquid column each time. Extremely easy to accurately repeat.

The outlet of the burette is only .030" and is 1½" long, a lot more restrictive than a carb jet.

[russhill]

Sam, I think your methodology for testing and quantifying viscosity is perfect. However, with all due respect, so what? It is certainly not clear to me how or if fuel viscosity correlates to engine performance. I presume this is your ultimate objective.

I believe fuel flow can be adjusted via jet sizes and/or needle valve for infinitely adjustability. Also the oils have different viscosities. And again adjust the needle valve. I think more is to be gained by adjusting oil to fuel ratios, because quantity of oil is NOT proportional to lubricity. Isn’t lubricity oil’s main role?

I agree that atmospheric pressure would not impact your test, but it directly affects engine performance. Temperature would affect your test, but that’s easy to control. Keep us posting your testing results and your thinking. I really enjoy it.
.

[FrenchPhil]

So like will 3% oil be slower than 2.5% at a given rpm ?

[russhill]

Could be. Why at a given RPM? We're racing, so mamimum RPM/HP is what we're talking about. What the optimum ratio should be depends on a number of variables, not the least of which is the oil.

[Mark75H]

Its a matter of concern to those using fixed jets.

[fyremanbill]

The greatest loss of fuel delivery will probably be due to the displacement of fuel with oil in higher ratios. It would be interesting to know if a lighter viscosity oil in the same ratio would flow more total volume. Adjusting fuel temp is probably the best way to increase mass fuel delivery with a fixed fuel system though.

[Mark75H]

Fuel coolers don't flow more because more fuel goes thru the jet, they flow more AIR because the cold fuel cools the air going into the crankcase, shrinking the air inside ... making more pressure differential between the crankcase and outside the carb.

I talked to the 2 stroke oil expert at one of the popular 2 stroke oil companies yesterday. I'm going to talk to more companies before I'm done. Several things surprised me. First he did not try to say his oil was any better than another brand. Second, he said all the best lubricating base oils were very thick and the lighter versions were just diluted with solvent to give them pour-ability and pump-ability. The solvents also give an advantage in mixing and staying mixed, but the primary use was thinning. Then he spoke about the balancing act of thinning the oil vs lubrication, and said lighter viscosity oil is just less lubrication in a 2 stroke. Third he said he is constantly bombarded with "your oil killed my motor" from guys who ran thick oil ratios with low octane gas thinking that more oil would compensate for the junk gas. He said there is no balance between junk gas and good oil, both must be good.

He said my demonstration would be a good visual demonstration of the viscosity of mixtures as used in 2 strokes and the respective flow of high mixes and light mixes.