I got a 98 f150 with a 4.2 in it and the plugs in it are autolite #764 witch is a short reach plug. There are a lot of plugs for this truck that are long reach. Why the difference and what's the best plug for it.

 

Motorcraft.

 

Motorcraft SP-479, sorry, SP-504, forgot you had the 4.2.

 

Are they short or long reach though

 

Are they short or long reach though

 

When in doubt, go with motor craft

 

The SP-504 is OEM, so whatever OEM is is what these are.

 

K thanks. Wonder why they would have long and short listed for same motor

 

Motorcraft and here is a picture of the exact plug you need for a 98 4.2. SP504

 

Because aftermarket makes plugs to fit multiple applications, OEM are designed with the specific engine in mind.

Just for an example, a Champion plug for your engine might also fit a Chevy and BMW (they don't, just for instance) and they all have slightly different specs, but the Champion is "close enough" to work. I know the 4.6/5.4 can be very picky with plugs, not sure about the 4.2, but OEM is pretty cheap compared to others, so just get them.

When you get into aftermarket/performance heads and pistons, then the short and long version of a plug really comes into play (as well as the heat ranges, but that is another topic).