<VV> Sparkplugs was "Pre-Detonation" (sic)

[Jim Burkhard]

Lloyd -

You must have missed my help of a couple days ago...

Again, there's no such thing as pre-detonation!  You are mixing 2 
terms that mean different things...  I'm not trying to pick nits -- 
understanding the difference would be helpful to solving your problem.

1. If your problem is occurring at low engine speed and high low, it 
is probably not caused by the spark plug choice, but is a "spark 
knock" (sometimes called "detonation") problem.  You either are:
	a. running too low an octane fuel. What is the actual PUMP octane? 
91? 93?
	b. have too high a compression ratio (did the problem start after a 
rebuild?  Did some "expert" rebuild the engine prior to you buying it?)
	c. have excessive ignition advance.  Now, I am talking TOTAL 
advance... that is the static advance you set during a tuneup PLUS the 
mechanical (centrifugal) advance built into the distributor PLUS the 
vacuum advance controlled by the vacuum advance assembly on the side 
of the distributor.  If some "expert" monkeyed with the distributor 
such that the mechanical advance weights/springs or the vacuum advance 
assembly is wrong, it may very well knock like mad because the actual 
advance delivered at a given speed/load point is suboptimal.

2. In the event that you had a true pre-ignition problem, it would 
*generally* occur at higher engine speeds.
	a. Again, what sort of engine speeds does this occur?
	b. In the event that you did have a pre-ignition problem caused by 
plug heat range, it would be caused by plugs that were too HOT, not 
too cold!  I don't know what your Autolite plugs cross-reference to, 
or if they are even appropriate for Corvairs (maybe they are a decent 
choice -- I dunno).  You may wish to try something more "tried and 
proven" like AC44FF, AC44FFS, or Bosch W8AC (not the platinum ones 
which some folks have troubles with).
	
3. Plugs that are "awful (sic) white" as you describe are unlikely too 
cold. More likely they are either too hot (which could cause 
pre-ignition) OR your A/F mixture is too lean. An over-lean mixture 
could exasperate a spark knock problem and could certainly increase 
tendency for pre-ignition because a lean charge burns slower, allowing 
more heat to transfer to the piston, and to the head via the 
combustion chamber and exhaust ports.  Again though, pre-ignition is 
more a problem on a HOT engine being driven hard at high revs, not 
toodling around town at low engine speed.
	a.  Does your engine ever "run-on" after you shut off the ignition? 
This is caused by chamber hot spots that would also cause running 
pre-ignition.  If you have run-on, the liklihood that pre-ignition is 
the culprit gets much higher.

4.  How well do those headers seal? Leaking exhaust ports can cause 
all sorts of issues.

5.  How did you jet the carbs after the headers? Still stock?

let us know some more details....

Jim Burkhard
CORSA


lloyd biggerstaff wrote:
> I am currently running Autolite 275 sparkplugs in my 102 h.p. engine that I have been having problems with predetonantion 
 >when the engine is warm and subjected to a load at low r.p.m.'s. 
Could this plug be too cold for the engine? I pulled a couple
 >of plugs and they seem awful white at the electrode. What are others 
running as far as heat range is concerned?The only mod
 >that I am running are headers.Any help would be appreciated.