Spark plug numbers...

[39portlander]

I pulled these out of the head on my 26 Fordor the first one (RH) has the longer porcelain and #25, the middle two are 407 and the last one 517.

I plan on just cleaning them up and reusing them but wondering if those different numbered plugs are different temps and I should get four that are all the same. Any input would be great.

 

[Royce P]

They are different heat ranges. I think the A25 would be the hottest, the one on the right the coldest. I would put the A25 in #1 and then keep them in order with the coldest plug at the rear.