Plug Reading For Power

The following is from a piece posted by Tom Rix on www.V8Buick.com 8/15/2006.

This is an article one of the SS racers shared. It's food for thought and I can attest that "most" people run the car too rich for max power! I use this religiously with good quality race gas in my cars. Also do not store race gas in your gas tank, it only "lasts" a matter of hours when vented. Don't mix brands either!

Plugs are best viewed with 10x power illumintated magnifying glass.

Heat range= Ground Strap: the ground strap indicates the heat range of the sparkplug. If the color of the groundstrap "changes" too close to the ground strap's end (which is above the center of the electrode) then the heat range is "too cold", meaning that the strap is losing heat too quickly to the base ring, and is not able to burn off deposits until near its end.

If the "color" of the strap changes near where it attaches to the base ring (last threaded ring), then it means that the plug range is "too hot" because heat is not transfered/cooled from the strap to the base ring quickly enough!! The strap might begin to act like a "glow plug", eventually causing preignition or detonation.

Proper heat range is when the "color" is at the halfway point on the strap, neither too hot or too cold.

(Color = meaning the evidence of heat/or lack of heat by the appearance of dark vs. lightened color of metal)

Jetting= the air/fuel mixture ratio : Shows up on the base ring (last threaded ring that has ground strap welded to it). You want a full turn of light-soot color on the base ring!! If you want to tune for max power, then you you want 3/4 to 7/8ths of a full turn of light soot color to turn up on the base ring. This is on the ragged edge of too lean but makes max power!

If the base ring has a full-turn of color, but there are "spots" of heavy build-up of "dry-soot" on top of color, then jetting is too rich.

Note: If the base ring has a full turn of color with some spots of heavy dry-soot, then jetting is too rich, REGARDLESS, if porcelin may be "BONE-WHITE", jetting is TOO RICH!!! Do not look at the porcelin to read jetting!!!

Porcelin=preignition/detonation: the porcelin will not accurately reveal jetting/airfuel ratios. To look for the first signs of detonation, search the white porcelin for tiny black specs or shiny specks of aluminum that have fused to the porcelin.

When detonation occurs, part of the air fuel mixture explodes instead of burning, the explosion heard as a "metallic knock". This audible knock is the result of a shock wave, this shock wave travels back and forth across the clearance volume "disrupting" the cooler boundary layer gases that cover the entire area, this disruptionallows more "heat" to be transferred into parts especially piston domes!! TROUBLE! with early signs of detonation, the shock wave will also rattle rings causing the tiny black specs. One step beyond the black specs will be tiny specs of aluminum coming off the piston tops. Then the porcelin cracks and etc.

center electrode = the very thin sharply defined porcelin ditch that encircles the center electrode will also show early signs of preignition, detonation or wrong heat range. look for signs of the ditch being filled with melted porcelin, you need a 10X magnifying glass.

The "ground strap" = heat range
The "plug's base ring" = jetting
The "porcelin" = signs of preignition/detonation

Thanks to Meaux Racing-maxRace Software

Tom Rix
Top Stock Buick 5433