Many times someone has said, "learn how to read plugs". Easier said than done- right? Well I've done some research and found a pretty good link. It's at;

http://www.4secondsflat.com/Spark_plug_reading.html

If anyone has additional information/links, please post them.

Here's another

http://www.dragstuff.com/techarticle...ead-plugs.html

 

Good page

 

In my opinion, The most useful thing about plug reading is getting the heat range under the limit. The porcelain will bubble and erode, and the electrodes can melt or erode if too hot (although there isn't much time between that condition and engine damage)(can retard timing and add fuel to cover up, but should go colder plugs).

Knock specs/peppering are useful too, but a knock sensor should be used, along with semi-conservative timing.

Mixture should be set with a wideband and engine dyno. EGT should be carefully monitored to make sure the result is rich enough to keep the engine safe. Power be damned EGT is too high, add fuel or pay the consequences.

If the plugs are too hot, your engine will not survive. Pre-ignition can set in easily and quickly wipe things out. Seized rings (if the body of the piston has enough mass to avoid melting a hole in the middle), damaged pins and rods, and even broken exhaust valves (chunks of melting plugs trapped in the seat at high RPM can hammer pieces of the valve off pretty quickly).

Also, even if you can get things set up on drag strip, don't expect it to be safe on say a mile long or other top speed blast. The stuff I work on has to pass a 300 hour, full throttle, 6000 RPM (6200 rev limit) test. We are doing a methanol (octane 115-130) application on a 1.5 and 1.8L, and found the plugs melting and causing pre-ignition after several minutes of WOT abuse (thus leading to the engine damages that I listed above), even with only 28 degrees timing and lambda .85 ish. EGT did NOT indicate a problem, though, and the advance was MBT and not over advanced. With methanol, EGT is easily lower than gas. 26 degrees and lambda .78 seems to work, although it reduced power and increased EGT. Max power was easily achieved with cooler plugs and leaner, but we needed to keep it safe enough so that fools who buy just any ole plug can keep the engine alive.

Happy tuning!