[AMC-List] response to Spark Plug question

["Dan Curtis" <d.curtis@xxxxxxx>]

Interesting question about the spark plugs. Back in the early 90s I used the 
original style Bosch Platinum plugs that were essentially a center fire type 
of plug.  They were completely overwhelmed by the big squirt when my 780 
Holley kicked in the secondaries.  At about 4500 RPM the car would start 
missing and backfiring until I took my foot off the throttle.  It only 
happened two or three times before I determined that the plugs were the 
problem and replaced them with an appropriate set of N12YC Champion plugs 
which resulted in the car running fine again.  Clearly these original Bosch 
platinum plugs were designed for the relatively low and very controlled fuel 
spray from modern fuel injection rather than a high CFM four barrel.

Now to your question regarding the Bosch 4 tip plugs, you need to keep in 
mind that an electrode can only arc to any one of the four prongs on a given 
cycle from the ignition.  Theoretically, because there are four prongs and 
only one of them can be the recipient of the arc at a time, they should last 
four times as long although there are so many other factors that affect the 
longevity of the plug I doubt that you would ever realize a four fold 
increase in the life of those very expensive plugs. The real benefit of 
today's modern plugs is the addition of platinum in the electrode due to its 
better conduction capacity than the other metals that were previously used 
in plugs of the past.

With today's unleaded fuels, the advent of readily available, low cost 
electronic upgrade kits to replace distributor points, almost any plug will 
last much longer than when your car's 343 engine was new.  I am sure the 
expensive Bosch plugs will work fine in your car.  I am just not sure you 
will effectively get any better results than everyday $1.99 plugs from 
Champion or Autolite.

Rather than go for the over price plugs, spend your extra money on the 
electronic ignition upgrade kit for your distributor, a new vacuum advance 
and new bearing and bushings for the distributor if you have not done so 
already.  By getting rid of the points, which do indeed start to run poorly 
within a year or 7,500 or 10,000 miles, and rebuilding the distributor you 
will eliminate a whole bunch of issue surrounding how your car runs both hot 
and cold (another old street racer trick is to get lighter weight springs so 
you will get faster centrifugal advance from the distributor at lower RPM). 
Also, if again you also have not done so already, be sure to get a good set 
of 7 or 8MM high energy spark plug wires with silicone rather than rubber 
insulator around the core.  The silicone based plug wires are not prone to 
insulator breakdown from heat and never have arcing problems in the rain 
like the old rubber based plug wires did.

One other thing to be on the lookout for is the coil tower being cracked 
which will also cause arcing to the distributor side of the coil and create 
a very poor running engine if any moisture is on the top of the coil.  A new 
coil cost about $25-30 for a standard replacement.  You can also go for a 
higher output coil if you have the electronic distributor upgrade and the 
newer silicone based wires and increase your spark by nearly 50%.  The high 
output blaster coil from MSD can be found on the net for about $45.00.

With these few low cost and easy to do steps, you will be amazed at how much 
better your car will run with regular old spark plugs rather than the Bosch 
which are way over priced.  If it were my car, I would do all the other 
things long before spending money on plugs that may not provide much 
benefit.  My new 390 motor which recently turned a whisker under 460 HP on 
the dyno did it with plain old Autolite platinum plugs for $1.99 each and 
that was the cost that the machine shop charged me for them.  I'll bet I 
could have found them on sale somewhere for $1.29 each.

My advice is to go for all the other things first and then after you have 
upgraded your ignition you still want to try the Bosch, give it shot and see 
if you can tell the difference.  I am betting the car will run and feel 
exactly the same as it did without them.

Regards,
Dan Curtis
d.curtis@xxxxxxx
602-317-2018 

_______________________________________________
AMC-List mailing list
AMC-List@xxxxxxxxxxxx
http://www.amc-list.com/mailman/listinfo/amc-list

or go to http://www.amc-list.com