Thanks, Dale. I've got .750" extended reach 4's & 6's coming in. I'll start with the 6's and see how they do.
Spark Plug Protrusion into Head?
- Thread starter AnthonyG
- Start date
Thanks, Dale. I've got .750" extended reach 4's & 6's coming in. I'll start with the 6's and see how they do.
Bored&Stroked
Well-known member
Yeah, there were not many heads made before WWII. I have a set of Eddie Meyers, but I just didn't want to work the Hell out of the combustion chambers to handle the big-*** cam that I'm running . . . so I put a set of my Navarro's on instead (not pre-war). Sometimes one has to compromise!
Pete
BANNED
Finding the right spark plugs for a new engine combination can be time consuming and a bit costly but it needs to be absolutely right if the engine is to run up to it's capability.
Before anything, they have to be the correct reach. That means the plug should have the same reach as the threads in the head minus the washer thickness so when installed there are no threads showing either on the plug or the head and the electrodes should not be exposed so much as to be touched by the valves or the piston in the case of an OHV engine.
If in a preliminary test the plug is short of the head surface,
you will need a longer reach plug.
If the plug threads go past the head surface, you either need a shorter reach plug or a SOLID copper washer of correct thickness.
The washer that comes with the plug usually is a compression type and is adequate for stock applications only.
If you want a bit more than stock, solid copper washers will give a closer "reading" and work better longer. It has to do with heat transfer. A plug is designed to be installed with all of the threads in contact with the head so stacking washers is not recommended. Most of the heat transfer is through the washer seat, not the threads.
In some cases if the correct reach plug is not available, one thread in the head can be chamfered away so it doesn't show.
After the engine is installed and running it can be driven as it is intended to be and the correct heat range can be determined. This is the expensive part of the project. Sometimes it takes 2 or 3 sets of plugs to find what is correct.
Before anything, they have to be the correct reach. That means the plug should have the same reach as the threads in the head minus the washer thickness so when installed there are no threads showing either on the plug or the head and the electrodes should not be exposed so much as to be touched by the valves or the piston in the case of an OHV engine.
If in a preliminary test the plug is short of the head surface,
you will need a longer reach plug.
If the plug threads go past the head surface, you either need a shorter reach plug or a SOLID copper washer of correct thickness.
The washer that comes with the plug usually is a compression type and is adequate for stock applications only.
If you want a bit more than stock, solid copper washers will give a closer "reading" and work better longer. It has to do with heat transfer. A plug is designed to be installed with all of the threads in contact with the head so stacking washers is not recommended. Most of the heat transfer is through the washer seat, not the threads.
In some cases if the correct reach plug is not available, one thread in the head can be chamfered away so it doesn't show.
After the engine is installed and running it can be driven as it is intended to be and the correct heat range can be determined. This is the expensive part of the project. Sometimes it takes 2 or 3 sets of plugs to find what is correct.
Pete
BANNED
I would not run it without a gasket. There would be a good chance of galling the seat, especially on an aluminum head.
Bored&Stroked
Well-known member
Good luck Tim, you'll figure it out!
I hear you. If these don't work, I've got Navarro's and Edelbrock's to choose from.
Thanks, Dale. Like Ronnie says, "It's all part of back yard hot rodding!"