<VV> (no subject)

[Mikeamauro at aol.com]

"...I'm going to reduce the timing advance further later today. but  what's 
your advice on the best timing range for this situation?..."
 
Jeff...
 
Reducing timing meets a point of  diminishing returns: moving much away 
from factory recommendations reduces fuel  economy. And, taking too much timing 
out can actually make the engine run hotter  (read: and make it more prone 
to pinging and detonation... the thing you are  trying to get rid of). Low 
octane fuel, hot spots in the combustion chamber, and  excessive engine heat 
all contribute to pinging (as does too much timing and a  few other more 
esoteric things ). Assuming you have a basically stock  engine, following are a 
few things to try:  have you removed the lower  engine shrouds and tried 
the cup of water down the cabs while running "trick" to  de-carbon the 
combustion chambers (don't try this unless you understand the  concept/method, 
completely)? I live in Florida; one of my Vairs is a 110, PG  with A/C (a 
combination very prone to produce ping). I run 18-degrees of  advance year round; 
however, lower shrouds are off April thru November.  This reduces engine 
operating temps by about 15-20 degrees, and is just  enough to get me through a 
typical Florida summer. If, after de-  carbonizing the combustion chambers, 
and removing the lower shrouds you still  get ping, more drastic measure 
are in order (not necessarily in this  order): check and deflash the cylinder 
head cooling fins; reduce the  combustion chamber quench space (.032 is 
optimum); verify carbs are not running  too lean; try different vacuum advance 
units (or modify internal spring  action of yours) for later application of 
vacuum advance. Corvairs were  designed for higher octane than is presently 
available from the corner gas pump;  hence, extra care must be taken in other 
aspects of engine  operation.    
 
Mike Mauro  


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