<< François Badoux wrote:
 >
 > Paul,
 >
 > I had an interesting chat with Tracy Crook last night.  We agreed that, as
 > far as we both observed, detonation happens always on the same rotor (with
 > possible exceptions which neither of us had the chance to observe... after
 > all we are not trying to cumulate detonation events too much...).  This
 > rotor is the rear rotor for Tracy, the front rotor for us, but it IS the
 > SAME rotor as our engine is turned 180° from his!
 >
 > A.      Do you know if it's a generally observed trend?
 >
 > B.      Has anybody found out the reason for this seemingly strange
 > behaviour? >>

Since detonation is charge temperature dependant, the coolant flow layout
puts the rear rotor housing at a disadvantage.

On stock 13Bs I think that the nock sensor is in the front housing where it
will never hear any detonation.

The rotor housings are quite flexible compared to the irons. When used very
hard (without detonating) you can see the edges of the housing turn black where
they scuff on the irons in the combustion chamber area.

When the kids get to 350-400 HP they add stock dowels to each case bolt
position in the combustion chamber side to do two things. First, it keeps the area
around the combustion chamber fairly stiff.
And second, it spreads out the torque load on the rear iron. When the HP goes
way up, the upper (generally) dowel fails the iron through the dowel hole/oil
gallery.

The rotors are being forced in the running direction as a result of the
expanding charge that is also pushing in the opposite direction with equal vigor
against the rotor housings. The rear housing is seeing twice that amount of
torque.

Should the rear housing detonate it is likely to detonated the next rotor
face (this is my thinking) because the rear housing is being distorted enough to
cause the seals to leak into the next face.

The major heat source in the chamber is the rotor face. So, oil cooling would
be the primary defense against detonation. Anything that increases charge
temperature adds to the problem. So intercooler effiecency, ambient air temp,
rotor temp, incorrect ignition timing, (limiting timing based on RPM) spark plug
heat range too high, ignition energy too low, and so on.

The street racers inject water passing through a certain boost pressure. Also
going way rich at high boost, and running the richer (my idea) of the 4
injectors on the rear housing. The water removes heat, slows flame front speed and
mimics a higher octane fuel.

For take off power I would tune for 150 degrees (or more) rich of peak EGT.
Once at cruise I would lean to lean misfire then enrichen back up 50 degrees of
EGT. The over lean mixture is slower burning and also mimics a higher octane
fuel.

Sudden throttle opening should be met instantly with retarded timing.

Best power is just rich of peak EGT (and the most heat in the charge) so stay
away from that location.

The NA engines are just about imune to detonation. Not enough heat of
compression. It is common in turbo engines, where the effective compression ratio
goes up with boost pressure.

Put the knock sensor in the rear housing.

Lynn E. Hanover

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