Comparable oil percentage.

[RandySmith]

I suspect Randy is right that the culprit is temperature.  I'm not at all convinced that adding a couple percent of oil to a gallon of fuel carries off significantly more heat.  Just from the general engine behavior(and being a chemist) I would lean towards the oil affecting the combustion process and reducing the amount of heat generated.  Trying some experiments with an LA 46 on hot summer days, adding a couple percent oil made a significant change in the sound of the engine run, even though it was running the same rpm.  The extra oil could easily be causing less burning to take place and leaving more residual exhaust in the cylinder on the off strokes of the 4 cycle.  The extra oil also made the engine sound much smoother, which is hard to quantify.  It just ran steadier, with less variation, and none of the hard, popping exhaust sounds.

Phil
Do you think there was any pre-detonation going on that was causing the hard popping exhaust noises?

Randy

[Howard Rush]

I like the idea of hit counts. Amazing what we can measure now.

So castor oil film is acting as insulation, and that's what's doing the cooling.  Interesting. Aren't there ceramic-coated cylinders or pistons these days?  Do they do the same thing?

[RandySmith]

I like the idea of hit counts. Amazing what we can measure now.

So castor oil film is acting as insulation, and that's what's doing the cooling.  Interesting. Aren't there ceramic-coated cylinders or pistons these days?  Do they do the same thing?

Howard, many of the  "plasma" sleeves and pistons, are simply anodized aluminum, I would think not about the mimic oil coatings.

There are still several things going on that cools motors maybe as many as 5, it is not just coating.

It is also interesting that some's definition of "coatings" is simply turning a few ten thousands or more of aluminum into aluminum oxide

Interestingly though Scott made a ceramic head for a airplane engine, It was extremely hard to get it into a 4 cycle, you had to turn the needle out as far as possible to try to get the engine to run rich, the head was so hot inside,and so cool outside, it just wanted to scream 2 cycle

Randy

[Brian Hampton]

As far as the number of "hits" the engine makes when 4 stroking, I think Scott Bair has proven quite conclusively that it fires on one stroke, misses the next etc. Brett Buck derived some graphs from Scott's pressure data which he's allowed me to use in my club's web page at http://www.holdfastmac.com.au/424stroking.html. I've used a microphone and computer (with a program called Goldwave) on an engine but mainly to determine the revs of my son's car engine. Even at just over 36,000 revs you can hear each individual exhaust pulse when it's slowed down 100 times. Quite fascinating.

But back on the subject of oil. Personally I don't think very much oil gets involved in the combustion process itself. I suspect most of the oil comes out of the fuel mix inside the crankcase as the methanol/nitro begins to evaporate (just take off a backplate and see how much oil is laying around inside) and then that oil begins to migrate up onto the cylinder liner/piston to do it's main job of reducing friction to a minimum. Once it's done this then it begins to migrate down to the exhaust port, probably as a film on the side of the piston, until it can escape. How long on average a particular bit of oil takes to migrate through is anyone's guess.