Do I really need a non-projected spark plug with this combo?
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 9,429
Likes: 44
From: Macon, GA
Do I really need a non-projected spark plug with this combo?
327ci. I'm running the .125 TRW dome piston, 64cc Edlebrock aluminum heads with a standard head gasket (.040) I think?
My machinists estimated the compression to be 10.3:1. I've been told by others here on the forum that it's so tight in the cylinder that I need a non-projected plug?
Here's what I know I need per Edelbrock:
Spark Plug Thread Size: 14mm
Spark Plug Reach: 0.750 in.
Spark Plug Seat Style: Gasket
Wrench Diameter: 5/8 in.
Anyone have any direct experience with this?
My machinists estimated the compression to be 10.3:1. I've been told by others here on the forum that it's so tight in the cylinder that I need a non-projected plug?
Here's what I know I need per Edelbrock:
Spark Plug Thread Size: 14mm
Spark Plug Reach: 0.750 in.
Spark Plug Seat Style: Gasket
Wrench Diameter: 5/8 in.
Anyone have any direct experience with this?
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
In case no one chimes who has BTDT, there's always clay. If it's so tight, I'd take the time to index a test plug where the strap isn't angled down towards the piston and then check by cycling the stroke. Of course, should the engine be assembled and installed at this point, there's the risk of the clay coming off the plug and/or sticking to the piston, so it's going to take some care. (I'd oil the portion that may contact the piston.) When you see where you are, you may end up indexing them all. Hope that helps if you don't get the direct feedback you're looking for.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I have 12.5:1 compression on an open chamber BB and use the same dimension plugs. If the heads use a 3//4 reach plug, the threads on the plug and the threads in the head should come out exactly together. If the threads don't match, you get a hot spot that will cause pre-ignition. My theory is that combustion chamber is gonna' have to be really, really full to get to the plug.. And very possibly way over your compression ratio now.
My next plug change is going to be a projected tip plug. I want to get the electrode out in the swirl a little more.
My next plug change is going to be a projected tip plug. I want to get the electrode out in the swirl a little more.
