Re: Causes of detonation

[Orin Eman <orin@wolfenet.com>]

Another thing to consider with the 3B is the high redline - 7000 RPM
with the limiter being about 7200 and setting the overrev code
at 7440 RPM (Note the Bentley notes possible engine damage if this
one is set).  (BTW, in comparison, the 10V ECU cuts the fuel pump
at 6700 RPM.)

High RPMs are very stressful to rods - puts them under considerable
_tension_ around TDC.  Then they are under considerable compression
on the power stroke and around BDC.  Usually, the tensile forces
are greater than the compressive ones _and_ rods (steel in general)
are stronger under compression than tension, so there is a greater
risk in increasing RPM than increasing boost _up to the point that
detonation or pre-ignition occurs_.  Once you get detonation, then
all bets are off if the ECU can't stop it and stop it quickly.  
If you get pre-ignition, then the burning mixture is going to be
trying to force the piston down when it's still going up...

There is the question of how you could get uncontrollable detonation.
There are limits of how much the ECU can retard timing.  Could
carbon buildup in the cylinder do it?  Could high RPM excursions
stretch and weaken the rods slightly, increasing compression ratio
at the same time?

Things to ponder.  Anyway, personally, I'm going to be setting
a mental redline more like 6500 RPM...

Orin.