Spark plugs will improve the horsepower of your vehicle by a miniscule amount.
Before you start booking an appointment with your local mechanic or registering your vehicle for the next drag race, keep in mind that we're just talking about power increases of one to two percent, so you won't be setting any record-breaking milestones simply by replacing your spark plugs.
When you replace very old and worn spark plugs with new ones, these improvements (1-2%) are likely to be reached.
In this instance, you're simply restoring your vehicle to maximum performance.
The concept behind spark plugs are that they will (and do) burn more fuel by providing more spark at the firing tip of the spark plug.
It is not essential to change to a different kind of spark plug if your vehicle is classified as 'high-performance' from the factory since the manufacturer will have already installed the most suitable type. If your basic car's engine has been upgraded, this will result in a different overall compression ratio. You will need to upgrade from stock spark plugs.
On the other hand, modern vehicles are so efficient and economical that they already ensure that they burn every last bit of fuel available.
This is due to the smart in-car computers and strong ignition systems that today's vehicles come equipped with.
