How much can you really tell by looking at a set of spark plugs? This is a subject that’s always controversial, and judging by the online debates we’ve seen, there’s a lot of misinformation and misconceptions floating around. Let’s see if we can sort some fact from fiction.
First of all, yes the spark plugs can tell us a lot about the state of tune of your engine and back when we didn’t have access to the tuning equipment we have now, the spark plug was the tuners best friend. These days we have access to quality wideband air fuel ratio meters, and sensitive dynos, so the reliance on reading spark plugs has greatly reduced.
So do spark plugs matter? Well yes and no but the key is understanding what information you can expect to gain.
It seems most people expect to be able to pull a 100,000 km old set of plugs out of their engine back in the pits and gain some useful insight into the state of tune of the engine at 8500 rpm and wide open throttle down the back straight on their last lap. If that’s your expectation then we’ve got bad news!
On the other hand spark plugs can back up the information that we’re seeing from the dyno and they can be useful in indicating a cylinder to cylinder imbalance. If you want truly useful information from the plugs though, you’re going to need to start with a fresh set too!