Friday, July 17, 2015

Some time ago, I came into a stash of spark plugs. I must have over a hundred NGK, Champion and Bosch plugs. All new in their little boxes just waiting their turn to ignite some fuel and burn it down the track.

In preparing to take this car to a rolling road or dyno as it's also know as, I started sorting out some different plugs I'd like to try, mostly various heat ranges as well as brands. When I got the car, it had NGK B6HS plugs in it. I've learned more about spark plugs in the last week than I had my entire life. 
Everything from heat range and why it matters to materials, indexing and reach. 

And reach is what this blog entry is to be about. Reach and why it matters. When I first pulled the plugs out, I must admit I thought they looked short. This being a full blown race car, I thought there must be some reason have yet to learn. I looked through my stash of spark plugs and saw I had quite a few NGK B7H, B8H and B9H plugs. Quick search of NGK's website and I found B means 14mm / 13/16” hex size, 7, 8, 9 is the heat range and H is the 12.7mm (1/2”) thread reach and S is Standard Type (2.5mm Center Electrode) Great, I thought. I have a few "colder" plugs I could try out on the dyno.

Then I began to think about REACH. The 1/2" reach just seemed too short. I took three different plugs and put them in a Spitfire head I had on the shelf. You can see in the photo, examples of REACH.

In the #1 cylinder is a NGK B-7H with the same reach as a B-6HS which is what was in the engine when I got it.

In #2 is a NGK BP6HS which means it is a Projecting Insulator Type thus the P and the S at the end means it is one unit hotter than a 6 but not a 5. A bit confusing but more on that later. 

Next, in #3 is a NGK BPR6ES - So B=13/16” hex, P = Projecting Insulator, R = Resistor Type, 6 = heat range, E =  3/4” thread reach, S = a bit hotter than a 6 but not as hot as a five. 

And #4 cylinder is empty. 

Here is a pic of the three different plugs

And here is the head that came with the car as well as the plugs.

Seems I need to change to the "E" 3/4" reach plugs as from the Factory.

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