Choosing The Right Spark Plugs For Your Custom Engine

Autolite, Bosch, Champion, NGK, and others offer race plugs that are generally much colder than production plugs, otherwise they offer little in the way of increased power. These are Bosch race plugs.

Any engine with high cylinder pressures will generally demand a shorter ground strap, which precludes the use of long-nose-reach spark plugs. The longer ground strap can turn into a heat sink, which can cause serious pre-ignition problems. This is especially true with nitrous.

Here's what happens when you run a too-hot plug in an E85-fueled engine at 12.5:1 compression. E85 is a very pre-ignition-sensitive fuel, and this plug literally melted. On E85, Champion recommends plugs three steps colder than a comparable gasoline heat-range.

On the left is a standard copper-core Bosch spark plug. In the middle is the Bosch Platinum, while on the right is the Bosch Platinum +4 plug, with four separate ground straps to increase durability. All three are offered in the same heat range, giving you a wide array of choices just within the Bosch lineup.

A common problem is interference between header tubes and spark-plug boots. Often, shorter plugs, such as ACCEL's shorty spark plugs, will minimize the difficulties. Other manufacturers also offer shorter plugs, but they are not necessarily called out as such.

ZEX (left) has specialty nitrous plugs that offer two different length ground straps. The longer, primary ground strap employs a copper core, while the three shorter-side-gap electrodes keep the tip clean. On the right is the E3, the latest entry into the specialty plug market. E3 claims its diamond-shaped opening around the copper center electrode offers improvements in emissions and mileage.