Magnum heads...what spark plug?

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dusterdoug

dusterdoug

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First question: Do the magnum plugs have 2 different reaches? 1/2" and 3/4"?
Projection tip or no??

I'm looking for a plug for an early 340 with EQ aftermarket heads, most likely a couple of heat ranges colder than the stock 340 application, but will start with the OE heat range first if needed.

Your input is appreciated!
 
I would look the casting number up to see what they came off of and get plugs for that application. You can fine tune them from there for your particular combo, but that will get you real close.
 
I always used Autolite 3924

Seemed to be just about right. Had a nice burn. I even use them on my edelbrock heads now.
 
Magnum heads (EQ's included) only use a 3/4 reach plug. I have a set on my 408 and am using NGK BKR6E. My engine is 9.8 to 1 compression. Depending on your compression ratio you may need to go up to a higher #. With NGK the higher the # the colder the plug

BTW: I hope you have adequate piston to head clearance. Early 340's had pistons that stuck up out of the hole and EQ's are closed chamber heads.
 
I ran NGK ZFR6F in my magnum. I personally prefer NGK plugs because I find them easier to read. Magnum engines used two different heat range plugs over the years. Earlier engines used a hotter plug (Autolite 3924, NGK FR4, Champion RC12YC, etc) but switched to a colder plug in around 97-98 (Autolite 5224, NGK ZFR6F, Champion RC12LC4, etc). For a while I actually just split the difference and ran NGK FR5 plugs, but they're a little harder to find so I just stuck with the ZFR6F since you can pretty much get it anywhere. Ultimately any of the plugs will work though, so pick your poison.
 
What plugs do you all run in a magnum motor replacing your LA? The LA plug or the magnum plug? Or will they both work.... just a personal preference
 
318willrun said:
What plugs do you all run in a magnum motor replacing your LA? The LA plug or the magnum plug? Or will they both work.... just a personal preference
Click to expand...

LA plugs that use the larger 13/16" socket don't fit magnum heads.
 
318willrun said:
What plugs do you all run in a magnum motor replacing your LA? The LA plug or the magnum plug? Or will they both work.... just a personal preference
Click to expand...

You should always use the plug that was designed for the engine your using, not something designed for another engine.
 
Trying the NGK FR5 plugs,as a baseline. Will adjust,as needed.
 
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