Tecnical Thoughts for Don

[lpugh]

Don I am a automotive tech with quite a bit of experience with high performance motors and tuning and enough two stroke experience to be dangerous. Something that has been bothering me is the difference in timing curves between 2 & 4 strokes and I have a theory. At 6k a 4 stroke will tolerate 6 to 10 degrees more timing depending on fuel and volumetric efficiency. We know the introduction of oil in to the combustion process will cause detonation to a motor that is tuned near peak. The theory being that the two stroke oil in the combustion process requires less timing in these motors which brings up there may be some additional risk to removing oil injection. Any thoughts one this?

[EuropeanAM]

Excellent question, Leon!

However..... I'm assuming that your referring to removing the oil injection from a 2-stroke, mechanically variable ratio oil injected engine (such as a 2.5L or 3.0L).

Although I PREFER to keep these engines injected (so as to retain the VARIABLE RATIO features).... most of these engines ran at approximately 70:1 at idle, and 50:1 at WOT.

At idle, although timing is important.... it's not NEARLY as critical as it is at WOT. We actually use "timing manipulation" to alter the engine's idle speed in many cases (with no adverse affects).

At WOT (actually, at approximately 5000 RPM's and above), the engine has reached it's maximum timing advance. Here, timing is FAR, FAR more critical, as detonation at these RPM's will (in a VERY short period of time) bring about MAJOR, CATASTROPHIC failures.

Since the mechanically variable oil injection system provided 50:1 fuel/oil ratio at WOT.... as long as the engine is RUN at 50:1 PREMIX RATIO (with the oil injection removed), the end result of fuel delivery and spark advance should be NO DIFFERENT at WOT. EXACTLY the same, as a matter of fact.

The PRIMARY concerns of using Premix (as opposed to oil injection) include:

-Richer mixture at lower RPM's than intended, causing carbon buildup and fouling
-The "human factor" (failure to achieve the appropriate 50:1 mixture due to "human error")

Good question!