Because they have different expansion rates, whether you’re running aluminum or cast iron
This style also has a second advantage. Because the electrode doesn't extend all the way over the tip of the plug, it's also shorter. Now, plug designers can extend the plug so that the tip extends farther into the combustion chamber which also helps improve combustion and—you guessed it—power.
But continued advancement in stock car racing engines has uncovered a flaw in traditional plugs with a J-strap electrode. In NASCAR's top touring series—Cup, Nationwide, and Truck—engine builders have been experiencing problems with the J-strap, which is welded on to the thread metal case, cracking and breaking off.
Some believe it's a product of the vibrations set up by very intense valvetrain movements and high rpm levels maintained lap after lap. Others think it's a product of very efficient combustion causing damaging pressure waves that can literally shake the J-strap loose.
Either way, it's not specifically a matter of horsepower because unlimited Dirt Late Model motors that produce equivalent power don't seem to have the same problems.
The E3 spark plug uses a unique electrode design that provides multiple points for the spa
As a result, plug manufacturers, like Champion, have produced what they call "surface gap" plugs. These don't have a single electrode at all and instead produce a spark that arcs from the tip of the plug to the metal casing. This design doesn't typically produce more power than traditional plugs using a J-strap design, so they are only recommended for applications where strap failure is a problem. But as engine designs in the lower levels of stock car racing continue to evolve, these plugs may become more prevalent by necessity.
The New Kid on the Block
At the other end of the spectrum from the surface gap plug design are the plug designs from a relatively new manufacturer, E3. Instead of a traditional J-strap, E3 plugs feature a three-pronged structure that serves as the electrode.
The design serves a couple of purposes, according to E3. First, E3's engineers say that their research shows a traditional plug loses some power relatively quickly as the electrode wears down from near constant electrical current.
Electricity flows most easily across a gap from one sharp edge to another. The E3 design creates multiple sharp edges in a complex electrode design so that the spark plug operates at premium efficiency for a longer amount of time. The electrode structure also has an opening directly above the plug, so even though there appears to be a lot of material for the electrode, it's still easy for the flame kernel to propagate throughout the rest of the combustion chamber.
We also suspect that the extra mass of the E3 electrode will be more resistant to breakage than traditional J-strap designs, and may provide a good option in applications where broken plugs are a problem. This is something we'll definitely have to look into further in another issue.