Big Block Spark Plugs

[79ramp]

Trying to figure out a part number here. I have a 454 which came out of my '79 C30. The spark plugs I took out (which I did not save because I am a moron) were sized for a 13/16" socket. When I pick-up new plugs, they are sized for a 5/8" socket and the threads don't even reach the hole before the 'shoulder' of the plug hits the head.

I am going to hazard a guess that the heads are not original so I am planning to check the date code, etc. on the head when I get home. In the meantime I was hoping maybe someone here might have an idea as to what # plug I need. I typically run Champion copper plugs in all of my engines but I am not going to be picky here as I am not keeping this one (it is the old motor going back in the donor truck which gave up a fresh motor to my ramp truck).

The 5/8" plugs did fit in the motor I took out of the donor truck so I don't think it was a case of just the wrong plug.

 

[WFO]

Newer heads use the small plug with a tapered seat, and older heads use the big plugs with a crush washer.

 

[79ramp]

Must be older heads or an older motor. Any idea when that cut-off happened? Pre-'76 as far as I can tell, 95% sure the motor from the donor truck is original.

 

[nvrenuf]

I'd pull a valve cover and get the head cast number so narrow down what they came off of. It's the only real way to be sure.

 

[MikeB]

I'd worry more about using plugs with the proper "reach". Too long and they stick out into the combustion chamber and maybe even hit a piston. Too short and they foul easily, and the threads get clogged up with carbon deposits.

 

[WFO]

I'm pretty sure it takes a Delco R44 or equivalent.