Ok, read carefully...

Better spark plugs do not increase horsepower. Crappy sparkplugs can cause ignition trouble which can decrease power. Do you think Mercedes would factory equip their cars with spark plugs that caused ignition problems?


The only time a different sparkplug could help is when you have moved the operating environment beyond the OEM plug's operating range (increase compression, swtich to ethanol, add forced induction, etc.).


That said... Denso iridiums are one of the most reliable and durable spark plug designs in the industry. I ran a set of them in my Spirit R/T for over 75,000 miles under high boost on pump gas. They worked like a charm.