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If this is a NA engine, you have a lot more choices. A non resistor plug will give a little more energy at the firing end but could induce some electrical inference to sensitive electronics. Most race plugs are non resistor.
Can you use a street plug in a racing engine. Of course, you can. The only person to stop you is yourself. If it survives, and the plug appears to “work”, go for it.
In most club racing 911 NA engines where a street plug is used, the engine probably does not make enough cylinder pressure to affect the street plug. In many cases the Ignition type limits the cylinder pressure developed and saves the street plug from destroying itself.
The simplest differences between the two plugs is construction and heat range. The construction has more effect on the plugs heat range. Race plugs typically use a thicker center electrode made from material that will withstand the abuse a race engine demands of the plug. Detonation, cylinder temp and pressures all work against a finer precious metal wire plug. Although it takes more energy to fire a thicker electrode. Most race engines have Ignition systems that can do this, more so that street engines.
Race plugs will typically have a shorter electrode, or less of it outside of the plug chassis. Shorter ceramic insulator as well. Often this is to shield the plug from the in-cylinder stress and in some cases also to give piston clearance.
Today, race plugs have taken on a whole new construction at both ends of the plug. Smaller chassis sizes are common now, 10.00mm and 12.00mm are standard sizes now. Finding 14.00mm plugs today is getting harder and harder.
We are using 10.00mm plugs exclusively now as there are more choices for different applications. I am seeing a convergence between plug construction for normally aspirated and turbo engines. What we use for either is more about the electrode position in the chamber. Now we are seeing extended firing ends into the chambers for Turbo engines. The DI engines have driven this technology with swirl “pots” built into the piston crowns trapping a small amount of mixture that the plug ignites. This technology is more about pressure and temperature-initiated ignition than spark ignition. It has opened the ability to produce more torque with leaner mixtures.
Looking at a 14.00mm race plug from any manufacturer you choose to use, it will have the appearance of an older style plug. However, it will last longer, give less trouble and will be easier to read the Ignition advance and fueling.
If you use a street plug with a fine wire, it can be read the same but typically the race plug will be cooler and will not show any boiling happening. Sadly, in many cases the plugs are never “read” and unfortunately some do not know how to.
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