Spark plug cross

notjustair · Jun 26, 2013

I'm looking for the folks who know something about plugs:

I bought new plugs for the grain truck. It had AC R43 in it so that's what I wanted to go with. I think the R means high heat range doesn't it? The truck doesn't burn any oil. It does run rich at idle but I have never had it foul any plugs.

Anyway, I got home from town and the guy at Auto Zone gave me AC 303. I didn't notice until now.

What is the difference between these two? They are gapped correctly - will they work? The truck is a 1958 GMC with the 270 straight 6. I really don't want to have to spend an hour in the car tomorrow to get the other plugs.

wisbaker · Jun 26, 2013

R means resistor. Numbers have changed, there are websites that can cross it for you. As far as heat range the numbers used to indicate the heat range. One of my previous employers had a not so old GMC one ton we plowed snow with. IIRC the recommended plug was a RY14, but they fouled out after one or two snow events. Put RY 16's in it they'd go a year between changes.

Dave Sherburne NY · Jun 26, 2013

Try this one. I think the R means resistor
SPARK_PLUG_CROSS_REFERENCE

notjustair · Jun 26, 2013

I had no idea there was such a thing! When I put in the old plug number it said the 303 was equivalent. Here is a link to the site:
Spark Plug Cross Reference

Revredneck · Jun 27, 2013

R - resistor
4 - 14 mm threads
3 - heat range
The old AC plug numbers were so easy to interpret. Sadly, they no longer use this system.
Good Luck and God Bless

Spark plug cross

notjustair

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wisbaker

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Dave Sherburne NY

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notjustair

Well-known Member

Revredneck

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