Someone once said...."don't confuse me with the facts, I already have my mind
made up."

First off, we are not talking about pre-ignition here. Fact; pre-ignition comes
from an alternative ignition source....other than the glow plug in our case.
Fact: the ignition timing in our compression/glow ignition engines is controlled
primarily by the compression ratio....period.

Other factors contribute and effect slightly the precise ignition of the fuel charge.
Lets keep the discussion on detonation.

Fact: Detonation can be caused by:

1. Lean fuel mixture
2. Fuel octane too low
3. Improper ignition timing
4. Lugging
5. Carbon deposits
6. Excessive milling of heads or block, which will increase compression ratio.

Lets examine these factors, and apply them to our glow engines shall we?
1. A lean mixture (not enough fuel in the air mixture) will burn out before the
engine reaches TDC and cause detonation...."engine knock". An ideal mixture
will burn in a controlled manner and apply maximum combustion pressure to
the piston just after TDC., at the end of the burn. Maximum combustion pressure
does not occur (or should not) at any time BTDC, or power will be lost....simply
because the piston is traveling in the wrong direction when the force is applied.

A rich mixture takes longer to burn. This is real simple to understand. A rich mixture
will reach maximum pressure later, or further past TDC. This will effect a slight loss
in power because the piston has traveled further down on the compression stroke.
The maximum power could have been developed if the force had been applied earlier,
at the proper time.

Fact: there is no circumstance where-in and engine will detonate due to a rich
condition. Nor will an engine detonate and backfire due to an accumulation of fuel
(resulting in a rich condition) suddenly "rushing" from the crankcase to the
combustion chamber.

A rich mixture can help overcome detonation, and mask it, and even prevent it....
but itwill not "cause detonation" in any way shape or form....that's a fact.

2. Although "octane" (gasoline) does not apply directly to our alcohol/glow engines,
the fuel in our case is still the second leading cause of detonation in our engine. A
high compression (even a European two stroke) will detonate like heck if too much
nitro is used in the fuel.

Keep in mind, my previous statements that will continue throughout....the
compression of the engine is what controls the ignition timing (advance) not the
carburetor, or the adjustments of the carb.

Fact: if you have a high compression engine (Euro) and it is designed to run on 5%
maximum....it will detonate like mad, with say....15% nitro. BTW, I just found this
out the hard way on a new .91 ASP 2-stroke.
Fact: there is no adjustment that can be made to the carb needles that will eliminate
the detonation. You can mask it, and you can extend the burn time to get it further
over the TDC point....but you cannot eliminate it without either lowering the amount
of nitro, or lowering the compression ratio by adding shims to the head.

Fact: (again) the compression determines the timing (firing) of the charge, not the
needle settings. The nitro makes it worse because the fuel burns faster, and hotter
Heat=Power.

Stay tuned....I'll finish this post later, examing the other causes of detonation.

FBD.