Need to identify correct spark plugs

callbald

callbald

Senior Member
I bought a 64 galaxie 500 with a 289 engine that runs rough at high idle and under load. So far I found:
Motorcraft APP3923 spark plugs that are not standard
aluminum heads and intake manifold (maker unkn)
Edelbrock 1406 carburetor
MDS distributor
Compression tests showed 165-170 pounds across all cylinders.

I know there is a miss so I am checking plugs and wires and timing. If I need plugs, what should I buy.
 
Aftermarket aluminum heads from different makers had different plug lengths. Best to replace plugs with the same ones. Maybe you can pull a plug and measure the thread depth to find a plug with the same length thread. Maybe the head brand is under a valve cover.
Several US companies had cheap copies of Edelbrock, etc. heads and intakes made offshore and sold them on ebay, etc.
 
Plug/thread length does not necessarily determine heat range of spark plug. They will need to be driven a while and "read" to dial them in if starting from scratch. A good starting point may be the present 7 that are firing. Any pictures of firing plugs available?
 
streetdreams said:
Plug/thread length does not necessarily determine heat range of spark plug. They will need to be driven a while and "read" to dial them in if starting from scratch. A good starting point may be the present 7 that are firing. Any pictures of firing plugs available?
Click to expand...

True, but the proper reach needs to be determined first when dealing with unknown heads. The former owner may or may not have used the right plugs.
To read plugs properly, you need to install a fresh set, then immediately do a full throttle acceleration run, shut off ignition while still full throttle, shifting into neutral at the same time and coasting to a stop. Pull the plugs and read before restarting the engine. Otherwise you're just reading idle or low RPM/light throttle conditions, which doesn't tell you much.
 
callbald said:
I bought a 64 galaxie 500 with a 289 engine that runs rough at high idle and under load. So far I found:
Motorcraft APP3923 spark plugs that are not standard
aluminum heads and intake manifold (maker unkn)
Edelbrock 1406 carburetor
MDS distributor
Compression tests showed 165-170 pounds across all cylinders.

I know there is a miss so I am checking plugs and wires and timing. If I need plugs, what should I buy.
Click to expand...
You might want to check in here for possible info on those heads www.spftech.com
 
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