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How to select spark plugs

2299 Views 4 Replies 4 Participants Last post by  echristie

After searching the archives, I have not found the answers to the questions. I have a '70 454, automatic, 3.42 gears, 180 t-stat, dual plane intake, Edelbrock AVS 800 cfm carb, Accel HEI, 8 mm wires.

There are Accel plugs in the car, but I found one has a cracked external insulators and there are some light brown colored carbon build up, so it isn't running to bad.

I want to know:
How you know what heat range to use?
What things influence spark plug choice?
Do you always run the recommended gap?
If not, what affect does opening or closing the gap do?
Is there a better brand than Accel? I grew up using Champions for everything, but I know there are other options.

Thanks in advance,

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AC's in my chevy's, nothing fancy. I've tried Motorcraft and Champions but AC seem to work the best.

I run the manufactures recommended plug, heat range and gap for the particular engine. I have only been able to get resistor type, maybe non-resistor can be special ordered.

If I convert to an HEI from points I use the same plug but gap it for the distributor. Non-computer GM HEI's use a .045" plug gap. AC plugs can be purchased with .045" gap already set but I check each one before installing them.

If the heads have been changed I make sure the plugs are correct for the new head. Some heads use a tapered seat plug and some use a washer type. I also the check the plug thread depth.

I think the heat range is a trial and error deal. If you run it hard, mainly drag racing, try a colder plug. I believe the recommended heat range is for general useage.

I use to think a tighter gap gave more RPM's but I haven't heard that lately.

My 2 cents!
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