Fire in the Hole Spark Plugs Part 3

FEat

When we last left, we talked about how a high powered ignition system can alter the way you read plugs. There are ways around it, but first, do yourself a favor and try this:

Pick up a copy of a spark plug tuning guide (all of the major plug manufacturers offer a high-performance pocket tuning guide booklet). Examine the correct color and appearance of your spark plugs and compare them to the guide. This should give you some insight into things like detonation, overheating, coloration and the like. Our “Fire In The Hole” article series is not intended to replace the spark plug manufacturer’s guide — but rather to supplement it.

There are several different (some expensive) spark plug "viewers" or magnifiers available on today's market, but one of the least expensive is a simple photographer's "loupe".  In essence, this is a simple plastic magnifier which is available in a number of different magnification powers.  The example shown is a 8X version.  By the way, these are available at any camera shop and are extremely inexpensive.
There are several different (some expensive) spark plug “viewers” or magnifiers available on today’s market, but one of the least expensive is a simple photographer’s “loupe”. In essence, this is a simple plastic magnifier which is available in a number of different magnification powers. The example shown is an 8X version. By the way, these are available at any camera shop and are extremely inexpensive.

 

There are several different methods to prepare for reading spark plugs, but in the case of a modified engine, there is only one right way to accomplish it. The engine must be shut off “clean”. By this, you should accelerate the car for approximately 1/8 mile and click off the engine, allowing the car to coast to a stop at a safe location. The idea is to remove the plugs and inspect them. Obviously, this type of clean shut off will be easier with manual transmission cars than it is with automatics.

I know it sounds elementary, but when you’re searching for the the ring on the spark plug, look in here (not the outside!).  Evidence is found on the insulator of the plug.  See the text for details.
I know it sounds elementary, but when you’re searching for the ring on the spark plug, look in here (not the outside!). An evidence is found on the insulator of the plug. See the text for details.

 

When it “fires”, the spark plug insulator transfers heat from the tip to the threads. If you look closely at a spark plug, you’ll see the point of effective heat transfer, which generates a ring on the spark plug insulator nose. The ring almost looks like a shadow and is more easily observed with a spark plug inspection light. The ring will form very quickly and is an indication of burning in the combustion chamber. The closer to the tip the ring forms, the richer the fuel mixture. The closer to the spark plug shell, the leaner the mixture. If there is no ring and the spark plug insulator tip is bone white, the fuel mixture is too lean (this information only applies to gasoline-fueled applications). The total range from rich to lean (ring near the tip to ring near the shell) may only take a change of seven to ten percent in the air-fuel mixture.

:  Ignition systems do not have an effect upon jetting and cannot change the air fuel ratio.  Jets do that.  But when a modern high powered ignition system is installed on an early automobile, the jetting will almost always appear lean.  Why?  Simple.  Today’s ignition controls offer much superior burning properties.  And because of this, changes may  be required in the air fuel ratio.
: Ignition systems do not have an effect upon jetting and cannot change the air fuel ratio. Jets do that. But when a modern high powered ignition system is installed on an early automobile, the jetting will almost always appear lean. Why? Simple. Today’s ignition controls offer many superior burning properties. And because of this, changes may be required in the air-fuel ratio.

 

When making the switch to a high powered ignition system, you may find that the actual fuel curve will have to be enriched by five to ten percent — the reason being that the ignition system is now burning more efficiently. In addition, the total spark timing might have to be reduced by approximately three degrees.

As you might have guessed, reading the spark plugs isn’t exactly a black art, but it isn’t an exact science either. You have a number of variables open to you — air fuel mixture, spark plug heat range, ignition timing, fuel type and a host of other things that are not in your control (ambient temperature, barometric readings, etc.). The idea is to make the most of your situation, and tune from there.

Next issue, we’ll discuss gaps and plug indexing. Stay tuned:

Email us - Support@RacingJunk.com
Call us - 867.326.9227
Copyright © 2005-2017 RacingJunk.com All Rights Reserved.

Designated trademarks and brands are the property of their respective owners. Use of this Web site constitutes acceptance of the RacingJunk.com
Terms of Use, Classifieds Disclaimer, Privacy Policy, and Cookie Policy