SPark Plug Difference
 

What is the difference between a Motorcraft SP450 ans a SP450a? both are listed for my F150 the difference in price on rockauto is like $.30 a pice and I just was wondering is one hotter than the other? and which would be best for my old truck.
She is an '93 F150 5.0 with 215K miles on her that I have barely ever done a thing to. Recently she has started a loss of power issue so I decided id start with a tune up since I cant even remember when I did the last one but Its been Ages thats for sure.

EFIs don't need tune-ups; that's only for carburetors. But all vehicles need maintenance, and sometimes repairs. Get a Haynes manual, read it (at least once cover-to-cover), and catch up all the recommended maintenance.

https://www.supermotors.net/getfile/...l/hayneses.jpg
(phone app link)

Using the highest-quality parts you can find & afford (instead of the cheapest, like most people do) and using the proper techniques pays off.

Doesn't the site you're shopping say what the difference is? Post the link that shows both plugs.

Really EFIs don't need a tune up? So I never have to change my Plugs, Wires, Cap & Rotor, Air Filter? I never have to check/adjust my timing? I'm sorry but that's just not true. Maybe you define all that as maintenance but for 30 years I have knows it as a "tune up" If you define a tune up as adjusting the air fuel mixture on the carburetor then yes, that's true EFIs don't need to do that.
No the site I am shopping on does not list the difference, if it did I would not have asked here, And A Haynes manual is your ultimate suggestion? I admit they are handy, and have their uses but they often glaze over important details and sometimes miss information all together. Such as the distinction between these two spark plugs. Both will work for my truck but I want to know if one is specified for a specific high heat application, or some other specific detail. I have since bought plugs so it no longer really matters.

That's a weird one. They show as either is proper for a whole list of cars. And the 450 is shown as a cross-ref for the 450a, but not vice-versa. Seems like the "a" would be some minor change, maybe for manufacturing or for improved design. Worthy enough for an "a" but not for a complete new number.

Also possible that the "a" is an economy, or lower quality designation, like Standard products T series.

https://www.rockauto.com/en/parts/mo...park+plug,7212