How to Select Spark Plugs for Your Engine

selecting the correct spark plugs for your engine has a lot to do with the build specs and the type of racing that you'll be doing choosing the incorrect spark plug type or running the wrong heat range can cause poor performance shorten the life of your plugs or possibly damage your engine but with some basic knowledge and some good information you'll be firing on all cylinders in no time at all the first choice you're going to have to make when selecting a spark plug is the type of electrode material there are three materials commonly used for electrode materials copper iridium and platinum copper plugs are the cheapest and most common option they feature a copper core electrode that's coated by a nickel alloy coating copper plugs are the best choice for performance and high compression applications since they tend to run the coolest but the downfall is is that they have the shortest lifespan and typically need to be replaced every 20 to 25 000 miles longevity is the primary benefit when selecting a platinum plug platinum is harder and has a higher melting point than the nickel alloy that's found on conventional copper plugs this allows them to burn at a much higher temperature burning off deposits and preventing fouling they are more expensive than the copper plugs but their lifespan can easily reach 100 000 miles or more iridium plugs are the top of the line and they service the same engines as our platinum plugs do but iridium can be as much as six times harder and eight times stronger and has a higher melting point than platinum does this allows the use of a fine wire center electrode that conducts electrical energy better and increases firing efficiency the lifespan of iridium plugs can be as much as 125 000 miles or better selecting the correct heat range for your plugs is also critical this is especially true in high performance applications heat range is a rating for the speed at which a spark plug can transfer the heat from the electrode to the plug to the cylinder head where it can be cooled by the cooling system the ceramic insert found on a hotter plug will have less contact area between the ceramic and the metal portion of the plug and allows less heat transfer most spark plug manufacturers recommend that you keep the electrode temperatures between 900 and 1500 degrees fahrenheit finding the correct heat range can be a little tricky since not all manufacturers use the same heat range scale some plugs get hotter as the numbers increase while others do just the opposite so be sure to check with the manufacturer before you purchase if the heat range you select is too cold the spark plug won't be able to burn off the carbon deposits causing a loss of spark energy select one that's too hot and your engine could experience knocking pre-detonation power loss or even engine damage hotter isn't always better and engines with high compression or that use forced induction see higher cylinder pressures and temperatures which can lead to pre-detonation quickly these scenarios require less heat from the spark plug to burn the air fuel mixture completely so selecting a spark plug with a colder rating will speed up the transfer of heat from the electrode tip to the cylinder head adding nitrous also increases cylinder temperatures and usually warrants the use of colder plugs to help counteract the higher temperatures running methanol while methanol may help cool the air fuel mixture in the intake it also creates a more complete combustion process in the cylinder which increases temperatures and will require the use of a spark plug with a colder heat range advancing your timing can also raise combustion temperatures estimates claim that cylinder temperatures can increase 70 to 100 degrees for every 10 degrees of timing advancement so to prevent knocking and pre-ignition you may need to select a colder plug the opposite also holds true here if your engine's compression is low the spark plug needs to provide higher temperatures in order to completely burn the air fuel mixture if complete combustion doesn't occur the unburned air fuel mixture will form deposits on the spark plug and throughout the combustion chamber since they tend to run a little hotter and last longer platinum and iridium plugs are the best choice for these applications ultimately to achieve the best combustion the heat range of your plugs needs to meet the demands of your application what's the best gap for my spark plugs that's a good question and ultimately it comes down to trial and error to find the largest gap you can get away with in your engine almost all forced induction and high compression engines will require a plug gap that's tighter than stock the increase in cylinder pressures and the denser air fuel mixture can actually blow out the spark if the gap is too large too small of a gap can cause the engine to run rough create inconsistent rpms and worst of all power loss re-gapping your plugs concentrates the spark for a more complete burn that resists blow out for applications with less than 15 pounds of boost gap your plugs between 26 and 32 000 for engines with over 15 pounds of boost you may need to gap your plugs as tight as 18 000 to prevent breakup a good rule of thumb is to decrease the spark plug gap in 5 000 increments until you obtain a stable idle rpm and you don't experience any breakup under full boost ignition systems that provide a hotter than stock spark can benefit from a larger plug gap plug gaps should be increased slowly in 5 000 increments until you have a nice smooth running engine with a tannish color porcelain tapered versus washered seats this topic is pretty straightforward but it's very critical that you don't interchange the two designs heads that accept the crush washer style spark plugs have a flat surface for the washer to seal on and typically require a torque spec around 25 foot-pounds heads that take the tapered style spark plugs have a tapered seat that's machined into the cylinder head this style plug should be installed hand tight then rotated an additional 1 16 to 1 8 turn depending on the manufacturer's specs it can be hard to tell the difference between the two seat styles on the cylinder heads but looking at the spark plugs makes it more obvious but when in doubt consult the engine manufacturer for the correct spark plug style required for your application another design difference can be found in the plug's terminal stud most modern plugs use a nut style terminal but there are some exceptions to this most small engines and off-road vehicles use the threaded design so be sure to confirm before you purchase and make sure that your spark plug boot is compatible with your spark plug terminal design some manufacturers offer spark plugs with a screw-on nut that can be used with both designs one final tip for someone that's looking to get every ounce of power out of their engine racers have been indexing spark plugs for a long time but it's a practice that's commonly overlooked by most people ensuring that your plugs are correctly gapped and you're using the correct heat range is top priority but going the extra mile and indexing each spark plug can increase its ability to obtain a complete burn and may even result in a power increase indexing your spark plugs is a simple procedure and can be done with just basic hand tools and an indexing washer kit by aiming the plug's electro gap towards the incoming air fuel charge prevents the spark from having to travel around the electrode this allows the spark to ignite the air fuel mixture slightly faster and more efficiently to index your plugs draw a reference mark on a visible portion of the spark plug ceramic body to indicate the position of the electro gap opening screw the spark plug into the cylinder head ideally you want the electrical gap to face the intake valve if the electrode opening faces away from the intake valve you can use indexing washers to change the plug's position now through trial and error you'll have to determine which thickness of indexing washer is needed to get the plug positioned correctly repeat the process for the remaining plugs and torque them to spec indexing the spark plugs on your engine can be one of the cheapest horsepower modifications you can do another factor to take into consideration is what type of ignition system you're using msd was the first to offer a multiple spark capacitive discharge ignition system and we actually recommend using standard copper electrode spark plugs with our capacitive ignitions we based our recommendations on the fact that specialty plugs tend to burn hotter the heat generated by iridium and platinum plugs combined with the multiple spark created by the msd box doesn't leave enough time for the plugs to cool off between firings eventually the spark plug begins to glow and the excess heat from the plug can cause the air fuel mixture to ignite prematurely causing detonation issues with our msd boxes we recommend using plugs that are one to two heat ranges colder than the factory recommended heat range ignition timing is yet another factor that you'll have to take into consideration when choosing spark plugs anytime you increase cylinder pressures with forced induction or nitrous you'll need to pull timing to prevent pre-detonation a good rule of thumb is to the timing two degrees for every 50 horsepower with a nitrous used and pull one degree timing for every one psi increase in boost pressure and as always make sure that your ignition system is up to par and functioning properly dielectric grease can solve a lot of ignition problems and can even help protect against radial noise a must have for your toolbox is msd spark guard it aids in spark plug boot removal and i use it when i'm assembling custom spark plug wires applying a fine layer inside the spark plug boot helps prevent moisture build up and help stop voltage leaks between the boot and spark plug as you can see selecting a spark plug is a lot like most any other engine modification and requires a lot of research take the time to do it right now and you'll thank yourself later to see our full lineup of ignition components visit us at holley.com

Channel: Holley

Views: 104,623

Keywords: accel, msd, spark plug, spark plugs, ignition, supercharging, turbocharging, timing, methanol, boosted, gapped, plugs, indexing

Id: HYJZ8Crek8Q

Length: 10min 26sec (626 seconds)

Published: Sat Mar 12 2022