Gearheads - best spark plugs?

The auto parts store has about 10 different options for plugs ranging from about $9.00 each down to $1.00 each for the bosch. Is there really a big difference? And what about the split-fires? There was a lot of hype about them a few years back, didn't even know they were still around but they are. My engine is a Mercruiser 315 MPI. I'll get the expensive ones if they are really worth it. Thanks.

I would go with resistor AC Delco plugs. Never had a problem with them.

Split-fires do not have the cooling rings in the ceramic, so they burn really hot. Some cases it burns the prong off damaging the motor.

Maybe in a four cylinder I would run Bosch Platniums but no need in your V8.


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You don't need any special plugs if your ignition system is in good working order.

If they can cross reference your stock plugs with NGK equivalents I would buy them. They are probably the best plug out there and are widely used in racing due to their good performance and excellent reliability.

And they shouldn't cost more than $3 each.

A/C Delco makes the proper plugs for your boat in marine application (stainless), or regualr spark plugs which is what I always used. NGK, Nippendenso, and Bosch make good plugs, but I would stick with Delco. Stay far away from Champion and Autolite.

Now leaves another question which is how often do plugs need changing. My opinion is not nearly as often as you might think in a boat, unless there is a running problem which with EFI there shouldn't be. I changed my plugs once in 900 hours, and everytime I checked them they had no noticable wear.

if they are platnium,they should last for a long time. i dont know about 900 hrs. though. i run ac delco platniums and change them every season,probobly dont need to, just somthing to do.