Why do spark plugs have different tip shapes and what are the differences? – Jalopnik

If you’re like us, you’ve been thinking a lot lately about the different shapes and lengths of spark plug tips. But chances are you’re nothing like us (good for you), and you haven’t thought at all about why the tips on some spark plugs are different than others. Maybe you’ve had more pressing things to think about, like, oh, we don’t know, literally any other topic. But that’s why we’re here, to answer the questions you’ve never asked.

However, keep in mind that there are important reasons why spark plug tips have different lengths and widths, and learning about these different reasons can help you better understand how spark plugs work. Alternatively, you can decide to excoriate us in the comments for the things you think we got wrong. Anyway, welcome! While you’re at it, check out these common myths about spark plugs.

The main reason spark plug points have different shapes has to do with the different needs of performance engines compared to your regular car or SUV. The cylinders in racing engines and turbo engines get hot with a lot of pressure and need cold spark plugs that do not extend very far into the cylinder. Regular consumer vehicles run better with hot plugs that fire close to the piston. That’s why many modern plugs have a longer threaded section and center electrodes that extend beyond the threads. The ceramic part of the tips differs for hot and cold spark plugs, and the shorter ones are used for performance engines because they dissipate heat better. Then for similar reasons you have single ground electrodes, multiple ground electrodes and surface hole plugs without ground electrodes.

What are excellent spark plugs? No, it does not refer to spark plugs attributing their own negative qualities and thoughts to other spark plugs. With protruding spark plugs, the center electrode protrudes from the center of the thread. With non-protruding spark plugs, which almost all spark plugs once were, the center electrode is flush with the thread. With both types of spark plugs, there is normally a ground strap or electrode that extends from the end of the wire and curves over the center electrode. That ground band is the small part that you adjust when you hold the spark plugs at a distance. Yes, we know that spark plugs are already gapped, but you should at least check the gap against your car’s manufacturer’s recommendations. The other way spark plugs are lengthened is by increasing the length of the threaded section, also called thread span.

Shorter, non-protruding spark plugs are still used on high-performance and racing engines. In powerful engines, longer spark plugs can ignite the air/fuel mixture too quickly, causing piston damage. Additionally, the forces in the cylinders of these engines are quite rough on the small ground strap, so plugs that don’t stick as far into the cylinder tend to last longer.

Why the change? That’s because premium spark plugs use precious metals, such as iridium and platinum, instead of nickel or chromium for the center electrode tips. Non-precious metals used in traditional copper spark plugs are softer and require larger points than iridium. Spark plugs sold today as “copper” spark plugs actually have center electrode tips made of a nickel and chromium alloy. Iridium is six times harder than copper. Its melting point is 4,435 degrees Fahrenheit (2,446 degrees Celsius), which is almost 1,800 degrees hotter than the melting point of nickel (2,651 degrees Fahrenheit, 1,453 degrees Celsius).

That means it takes much longer for iridium to erode. It also means that an iridium tip can be much smaller and still do its job. It’s true that iridium doesn’t conduct electricity as well as copper, but believe it or not, that’s not as important as ionizing the orifice with as little current as possible, which the smaller size of the iridium tip does. That doesn’t mean smaller is always better. WeaponX has released a whitepaper showing that the performance of a 0.4mm tip is actually worse than that of a 0.5 or 0.6mm tip, which seems to be the sweet spot. That said, high-performance and racing engines still often use copper center electrode plugs, as the smaller points don’t handle heat as well and can form hot spots.

But you don’t want a plug that gets too cold. Most consumer vehicles have hot plugs that operate at the higher end. The cylinders in these engines do not get as hot as high-performance engines. If your spark plug gets too cold, it can become fouled much more easily. Obviously, you want plugs that are specifically in the right heat range for your specific vehicle.

How can you tell if a spark plug is hot or cold? One way is to look for a number printed on the side of the plug. The problem with that is that each manufacturer has their own numbering system, so you’ll have to look it up to know what the number means. Another way you can see this, and the reason we’re talking about this in this article, is to look at the ceramic tip of the insulator that holds the electrode. If you look down into the plug (or at the cross-sectional image above), there is a gap between the insulator and the housing. The deeper the opening, the hotter the plug, because it dissipates the heat deeper into the plug, rather than dispersing it close to the end.

You probably already knew that. But did you know that some spark plugs come with as many as four grounding straps? This configuration should ensure that the plug lasts longer. You see, even if there are four ground straps, there will still only be one spark when the plug ignites. And the spark will follow the path of least resistance. So if one belt is dirty, dirty or worn, the spark goes to one of the other three belts, reducing plug failures and extending plug life. And even if all four belts are good, the wear can spread across them since no one plug will necessarily be hit by the spark all the time. Do four-strap plugs perform better than one-strap plugs? No, but that’s not the point. The point is that they should last longer.

Is it worth upgrading to a plug with multiple ground electrodes? They do last longer, but since single-belt iridium plugs are expected to last 100,000 miles anyway, is this really a problem? Some drivers never even replace their spark plugs. We obviously do not recommend that. The longer the plugs are in, the more likely they are to break off or damage the cylinder threads when you try to remove them.

Wondering if you should upgrade to one of the other types of plugs we mentioned? Automakers have already made most of these decisions for you. The decisions most customers have to make have nothing to do with tip shape, but rather whether they should buy the cheaper chrome/nickel plugs or the more durable iridium or platinum plugs. So take a look at our handy guide to the different types of spark plug materials.

Spark plugs look pretty simple on the outside, but don’t let that fool you. There’s a lot to be said about spark plug design – more than we have room for here. We could probably write a whole book about it. However, nothing stops you from sharing your knowledge in the comments. Are there things about the shape of the spark plug tips that you think we missed? Let us know below.