The Stovebolt Site Forums The Shop Area Engine Shop Spark Plug Problem

Running a 250ci with GM HEI plugs gapped at 45 also have tried a 40 and 35 gap and always same problem, electrode worn at about 6000 miles, is this normal or do I need a colder or hotter plug?
No fouling and plugs have a light tan on the ceramic!

Are you using resistance-type plug wires? It sounds like the spark is a little too hot, and the gap is widening because of too high a current flow across the plug. I've seen this, and also burnung of the carbon center button in the cap when stranded metal wire was used, instead of the graphite-filled string core resistor wire.
Jerry

Jerry I am using 8mm high energy suppression wire is this the wrong ones to be using?

That sounds OK. It's the metal-core racing wire that seems to cause the problems with plug erosion. You might check the resistance of the wires with an ohmmeter. There should be at least 3 or 4 thousand ohms on a proper resistance wire. The longer the wire, the higher the resistance. A maximum of 1,000 ohms per inch is acceptable, but considerably less is OK.
Jerry

Also, shouldn't the gap be wider? When I installed the HEI in the 235, Tom Langdon recommended the gap be (if my memory serves me) 75 thousandths.

Anybody else have input on recomended plug gap with HEI?

You can try a wider gap, GM and Ford both had gaps of up to 80 the first year or two. GM ran into problems with internal cross-firing with the distributor cap, determined .042-.045 to be the "proper" gap. I found a reference on the MSD website saying to try .055-.060.

The reason for the wide gap settings in the early 80's was because of the extremely lean mixtures they were running back then. It was hoped there would be at least a little combustible mixture in the gap area if it was wide enough. It worked; I could set gaps in the 35-45 thousandths range and get a miss, and go up to 60 to 80, and run smooth! With normal mixtures, 45 thousandths is about right.
Jerry

Good sugestions. Also you might try copper core plugs. They handle high heat better.

Thanks for the input I will try gapping at 55 thousandths and see if it helps, as always there is so much knowledge on the bolt
thanks
jim

What do you mean by "worn"? You put them in at .035" and 6000 miles later they're at .070" or what is it that you mean?
I'm not reading that you actually have a problem. "No fouling and plugs have a light tan on the ceramic!"
What kind of plug and heat range are you using?
I'm using AC R44TS and have had a stock GM HEI in the 292 for about 15 years. I usually change the plugs every five years whether I need to or not.

.035"

Update, put new plugs in and gapped at 55 thousandths not only does it have a little more throttle response but it will idle down the road in 5th gear which it would not do before, thanks for all advice.
jim