Classic Mustangs List Archive

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Mail From: Peterson, Keith (email redacted)

If the majority of the pressure from the burning fuel does not or cannot
coincide with the piston's downward direction of travel the pressure will
increase to a point that "self" ignition will occur in the unburned fuel -
thus creating PING and KNOCK.

The faster a fuel can burn the higher the likelihood of creating a second
ignition point within the cylinder _because_ the pressure will increase
during the fuel burn. Initially the spark ignites one point of the fuel and
a hot piece of carbon, valve tip or heat/pressure alone ignites another
point in the unburned fuel.

The "ping" we hear is (usually) the two flame fronts meeting/colliding. This
meeting is very hard on everything. Engines are designed to have a
controlled burn, not a "Slam/Bang". Hopefully that ping sound was not the
piston receiving a hole in it or your head gasket shifting sideways - well,
that last one might be more like a whoosh. Either way, Piston or Gasket,
your engine could quickly become an extremely good "engine brake" - causing
all motion to stop in the drive line. Further causing your drive wheels to
lock up (long skid marks?) or break some other part of the car...

Here is something different to help make it really simple: two examples
--------------------
Given the same Fuel/Air mixture - 14:1
Given the same compression ratio - 9:1
Given the same RPM and load - 3000, level ground
Given the same volume of charge (bore, stroke, head volume) in the same
engine...

very hypothetically - (this is NOT accurate, only for example)
- High explosive material will "Burn" completely in 0.01 milli-seconds.*
- Regular Octane will "Burn" completely in 1 milli-second.*
- High Octane will "Burn" completely in 2 milli-seconds.*
- Diesel Fuel will "Burn" completely in 10 milli-seconds.*

*only one of these time sequences is correct for the engine in this example!
one milli-second! Anything under a 0.9 milli-second burn will cause Ping
(remember this is hypothetical). Anything over 1.5 milli-second is too slow.
---------------------
OKOKOK! now let us look at a higher compression engine...

Given the same Fuel/Air mixture - 14:1
Given the new compression ratio - 11:1
Given the same RPM and load - 3000, level ground
Given the same volume of charge (bore, stroke, head volume) in the same
engine...

very hypothetically - (this is NOT accurate, only for example)
- High explosive material will "Burn" completely in 0.005 milli-seconds.**
- Regular Octane will "Burn" completely in 0.5 milli-second.**
- High Octane will "Burn" completely in 1 milli-seconds.**
- Diesel Fuel will "Burn" completely in 5 milli-seconds.*

**only one of these time sequences is correct for the engine in this
example! one milli-second! Anything under a 0.9 burn will cause Ping
(remember this is hypothetical). Anything over 1.5 milli-second is too slow.

-----------------------
The higher the compression, more squeeze friction is created, the "Hotter"
the mix the... the blah... the yak... etc.


KPeterson,den,co,'71 r-top
- very limited amount of editing of original post - -
-----Original Message----- deleted - too many other posts since - -

Well. Walt, it seems that I could not leave it alone...

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