who is wrong?

[lucky bagels]

So go to Walmart buy Autolite plugs size 25, just like there little computer tells me. get home take my old plugs out and they are the same plugs just size 26. does anyone no the correct size spark plugs for a 1989/302 (25 or 26)

 

[95GTAODE]

The number describes the heat range, not necessarily the size. 26's are one heat range warmer than 25's... Depending on the year, 302/5.0 engines did use different heat ranges... For '87-'95 Mustangs, 25's are correct.

 

[skunk21]

just like 95GTAODE stated the # is the heat range. The stock plug is #25 though so walmarts computer was correct.

 

[lucky bagels]

thanks guys.. but wouldn't you want your plugs colder? or not

 

[skunk21]

thanks guys.. but wouldn't you want your plugs colder? or not

If you have a power adder. even then 1 step and maybe 2 steps. If you are changing your heat ranges and on a N/A engine you should be well versed in reading spark plugs and figuring out how to correct the problem, ie air/fuel. there are different reasons for changing the ranges and I don't know them all but anything from carbon foul to detonation problems.

 

[myslo50]

isnt autolite #24 the stock heat range for a 5.0

 

[HISSIN50]

isnt autolite #24 the stock heat range for a 5.0

As said, 24's are one range colder than stock. I run them in my cars without incident but 25's are indeed stock.

 

[Fast63]

you generally want a colder spark plug for an increased compression ratio or adding a power adder, so just increased compression in general. Might want to if your cam changes your cylinder compression enough.

 

[fford]

would you want to change heat ranges with alum. heads? I just bought a set and they are on the way. I already run the 24's.

 

[Fast63]

would you want to change heat ranges with alum. heads? I just bought a set and they are on the way. I already run the 24's.

I would use whatever spark plug the cylinder head manufacturer recommends. It should be listed in the instructions somewhere, and will likely not be autolite 24-26.

 

[HISSIN50]

would you want to change heat ranges with alum. heads? I just bought a set and they are on the way. I already run the 24's.

The alum heads will call for their own series of plugs.