- Dirt bike & ATV parts


The Famous Oil Ratio Test Article - Where is it ?

Dec 3, 2004
I have often heard mention of this famous "premix oil ratio test" article where they found the optimum premix ratio to be 32:1 but no one ever quite knows where it is.

Anybody know any info about it or have a link to it?

I think it might have been written by Bob Greene. Not even sure who that is.

I'm not talking about the one from Cycle Magazine Feb '78 that was written by Gordon Jennings.

Thanks a bunch for any help.
- a d v e r t i s e m e n t -

Aug 13, 2000
Sorry I do not have a link to any such write-up.

I was involved in an oil ratio test for Mercury Marine. We tested various oil ratios on a few different outboard engines that were commonly used in racing. We did not test every engine, as many engines were similar designs with different rated outputs (a common trick in outboards). We partly based our testing on some industry information by a chain saw and go kart engine company (Mcculloch).

In any case (for the most part) the oil used was Factory outboard oil. We did try other oils without much HP difference.

Oil ratio's covered the extreme range.

The bottom line is that more oil made more power. The standard 50 to 1 ratio was sufficient to provide lubrication without operational problems such as smoke and plug fouling. 32 to 1 made more power and 16 to 1 made even more power. We even tried ultra rich ratio's like 8 to 1 or 5 to 1 and power did improve to a point even at the extreme end of the test. 100 to 1 did show a significant loss of power. This was not designed to be an oil test to end all tests, just a way to determine how to make more power for certain racing classes,

While the test was not designed to indicate wear, I did draw some basic conclusions. In racing applications more oil reduced wear slightly. This is as you might expect. What we saw is that any normal oil ratio protects the engine well. Lean oil ratios seemed to work well until the temperature and stress got out of hand. That is where a lean ratio would not be enough for full protection.

I have since read that oil ratio's around 32 to 1 provide nearly all the protection that is available for most performance engines. My experience backs that up. Yes, there would seem to be some extreme examples of engines that need 16 to 1. I am not sure I can draw a conclusion as to which engines need this level of lubrication, but I would guess it would be well out of the norm, especially for dirt bike applications.

Another note on 2 stroke lubrication, upon teardown, any reasonable ratio will leave a significant amount of oil on internal engine parts. While many people think the oil just races through a 2 stroke engine, this really is not the case. It does separate from the gas and lubricate the bearings, con rod, and piston skirt in full force.



Jan 17, 2001
Thanks cujet. Good post.


Jul 29, 2000
South America
Rick Sieman:
"A second test they performed was to run synthetic in two identical engines and one was run at 24:1, the other was run at 50:1 The engine that ran 24:1 had less piston skirt wear, and less rod bearing wear, but had the same main roller bearing wear as the engine run at 50:1. "