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Sep 4, 2020

What are the best spark plugs for an RB26 engine?

R7436-8 double fine wire iridium spark plugs

What are the best spark plugs for a RB26? 

Best is a tough word, because the best for me, the best for the engine, may not be the best for you based on a number of factors.  There may be a money thing, there may be a brain blockage due to old school thinking. Its cool, we have seen it all. 

As far as spark plugs go, their job is to provide a place for an arc, or a spark to occur, to light off an air/fuel mixture in the combustion chamber of an engine. A spark plug that does that, may be the BEST spark plug for you. It does its job, it lights the mixture. 

However when it comes to a boosted, doubled and tripled horsepower engine, you may need a different spark plug to fire that mixture. You probably want a cooler than stock heat range, you may want a different type of material. 

Electricity looks for the path of least resistance. If its easier for the spark to arc anywhere other than the combustion chamber, it will. Electricity also likes sharp edges (think lightning rods). From my discussions with spark plug engineers, they say it takes 5,000 less volts to arc an iridium fine wire plug, than a conventional electrode plug. 

In a turbo car, you can turn the spark plug into a bit of a hot spot, or even glow plug like, where it is hot enough to spontaneously cause the air/fuel mixture to ignite.  You don't want that. 

The non projector, double fine wire NGK plugs, are the best plugs I know of, and have used for over 15 years. When price is no object, these are the plugs I use.  The heat range I use depends on the car use and horsepower.  Normally its a -8 to -10.  The 10's being the coldest, and running those on the road courses on a hot day. 

So whats the best plug for an RB26dett?  I say its the :

You are welcome to run old school copper plugs. Make sure you get the right length (The K's are shorter than the C's so anyone telling you to run a shorter plug, check and make sure they know what they are talking about) , make sure you change them often. Learn how to read them. Keep the rest of your ignition system in top shape, to make up for a harder to fire spark plug. 

Mark showing spring location in an R35 plug. Top plug is a K, bottom a C. 

Mark showing spring location in an R35 plug. Top plug is a K, bottom a C. 

Imagine making the spark have to arc across a gap you create, because you use a plug that is too short, then it has to arc in the combustion chamber. Electricity takes the path of least resistance. This gap you have created, if the spring isn't in contact with the top of the plug is high resistance. 

Breakdown of NGK spark plug numbering system.  Each letter and number means something

"Although the NGK factory will set the gap to a preselected setting, this may not be the right gap for your particular engine. The incorrect plug gap for your engine can contribute to a high rate of misfires, loss of power, plug fouling, poor fuel economy and accelerated plug wear. It is always best to check the gap against the manufacturer's specifications. If adjusting the gap on fine wire or precious metal plugs such as platinum or iridium, be very careful not to apply any pressure or prying force to the fine wire center electrode or insulator as they can be damaged. The gap should be adjusted by only moving the ground electrode. 

Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology) you can open the gap from .002-.005"."

The Great Spark Plug Debate: Separating Fact From Opinion - Engine Labs

"One of the most contentious areas of disagreements surrounds fine-wire spark plugs. It seems that everyone has an opinion about platinum and iridium plugs compared to the standard copper-core version. We’ll just start by saying that there’s a good chance that whatever you’ve read or been told about fine-wire plugs is probably incorrect." Read more

Spark Plug heat range chart
Spark Plug heat range chart NGK, Pulstar, Denso, Champion, Bosch

Project Farm did some testing on a few different spark plugs. With some results that I didn't expect. As he is, I am pretty skeptical of claims. 

E3, Pulstar, Autolite Racing, NGK Iridium, and NGK Copper spark plugs tested for fuel efficiency performance and visually observed for burn characteristics.

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