<VV> Plug questions - Pre-ignition and pinging

[Sethracer at aol.com]

In a message dated 1/13/2009 12:00:26 P.M. Pacific Standard Time,  
dave.thompson at verizon.net writes:

"The hot  tip can also promote pinging."  I have a set of new
AC42F's in stock  (listed as a cold plug). If I installed them, could I
advance my timing a  bit and still not have pinging? Or are there a number of
other issues to  contend with? 





There may be several issues at work. This is my opinion -  (two and  one-half 
cents worth)
I think the hot tip promotes pre-ignition, not an accelerated flame front  
(pinging). Although the symptoms are similar, pre-ignition is caused by a hot  
area remaining after the burn, and the incoming charge is ignited early. It may 
 still burn, as opposed to explode - which it what pinging is. As an example, 
if  the ignition is fired off early, the cylinder pressure pushes down on the 
piston  as it is still rising up on the compression stroke, holding down the 
power  input. If the flame front speeds up from burn to explosion, that too 
can press  down on the piston top - hard - that is the sound you hear, the 
explosion, and  that will cause loss of power as well. But pinging can take place 
even after the  normal ignition point, and can still cause loss of power, with 
the explosive  hammer blow on the piston expending the expansion energy of the 
gases, then  there is only a small increase in pressure to keep pushing down 
the piston. Of  course, pre-ignition can lead to pinging, if the flame front 
burn hits the major  portion of the fuel, just as the piston has reached full 
compression - the rest  is often going to light off with an explosion. So the 
cooler plug may  prevent pre-ignition, giving you back some power. It might aid 
any pinging  problems, too. But the cooler plug may be more prone to fouling, 
if it is  running too cool. A hotter after-market ignition might be a help 
for this.
 
Seth Emerson  - Opinions are like belly buttons
 


Seth Emerson

C's the Day! -  Corvair, Camaro, Corvette




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