- City
- Rock Hill
- State
- SC
Hey guys, so I am rebuilding my heads and when I was putting one of them back together I was testing whether the valves were closing completely where I put the spark plugs in the head for the test. As I was eyeballing the valve fit I realized my spark plug electrodes were wwwaaaaayyyyyy up inside the threads of the head and not anywhere near the actual cylinder ceiling.
I will need to get another set of plus, and will take my calipers to the auto parts store and get spark plugs that have a thread length or "reach" that is as close to or just under 3/4 an inch as that is how long the threaded portion of the heads spark plug hole is. I may take the whole head with me!
The plugs I have been using are too short, which can cause detonation due to the spark being buried way up in the thread well. The spark isn't near enough to the chamber to get it all ignited quickly so the spark is super delayed and the timing is really off the mark.
What is spark plug reach? A spark plugs reach is calculated by the length of the threads. It is measured from the seat of the plug to the end of the threads; it does not include the electrodes, or any extended metal shell. (from the NGK site)
Here are some links about Spark Plug Reach in case you were wondering what this is all about.
Motor Trend article on Spark Plug Reach
Summit Racing page on Spark Plug Reach
Here is where the plugs I have today sit back in the head:
So, my heads are Chevrolet Performance Vortec heads that I bought off of Summit. While Summit and Chevrolet spec sheets that were on the Summit site did not say what spark plug to use, in the Q/A section, a few folks had asked what spark plug fit the heads and a few folks / Summit responded that an AC Delco 41-993 fit the heads. Here is what that looks like: (click on it to blow it up)
That is a perfect fit!!!! I am looking forward to seeing what a difference this makes as I've likely never used the correct plugs. Live and learn!
If you have in-person friends who are also car nuts who will sit around the shop/garage/parking pad and help with your projects or at least BS about them, hold on to them! I don't know anyone locally who knows jack squat about cars other than the old dudes in the local car club. I'm about to join said car club and become an old dude so I hope to BS about cars at least once a month each summer going forward.
I will need to get another set of plus, and will take my calipers to the auto parts store and get spark plugs that have a thread length or "reach" that is as close to or just under 3/4 an inch as that is how long the threaded portion of the heads spark plug hole is. I may take the whole head with me!
The plugs I have been using are too short, which can cause detonation due to the spark being buried way up in the thread well. The spark isn't near enough to the chamber to get it all ignited quickly so the spark is super delayed and the timing is really off the mark.
What is spark plug reach? A spark plugs reach is calculated by the length of the threads. It is measured from the seat of the plug to the end of the threads; it does not include the electrodes, or any extended metal shell. (from the NGK site)
Here are some links about Spark Plug Reach in case you were wondering what this is all about.
Motor Trend article on Spark Plug Reach
Summit Racing page on Spark Plug Reach
Here is where the plugs I have today sit back in the head:
So, my heads are Chevrolet Performance Vortec heads that I bought off of Summit. While Summit and Chevrolet spec sheets that were on the Summit site did not say what spark plug to use, in the Q/A section, a few folks had asked what spark plug fit the heads and a few folks / Summit responded that an AC Delco 41-993 fit the heads. Here is what that looks like: (click on it to blow it up)
That is a perfect fit!!!! I am looking forward to seeing what a difference this makes as I've likely never used the correct plugs. Live and learn!
If you have in-person friends who are also car nuts who will sit around the shop/garage/parking pad and help with your projects or at least BS about them, hold on to them! I don't know anyone locally who knows jack squat about cars other than the old dudes in the local car club. I'm about to join said car club and become an old dude so I hope to BS about cars at least once a month each summer going forward.
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