22 May 2013 //////Does anyone know what spark plugs go in the 1955 Studebaker Commander V8./////// Hey, now you're bringing up a subject I can relate to. I was in the small engine business and had the good fortune of having a Champion OEM rep for a friend and customer. He supplied me with a considerable amount of information thru the years. It was in utmost secrecy that he gave me a "heat range chart." With that you can pick different plug styles and still stay within the suggested range. It can also of course allow finding one with higher or lower range if so desired. When I purchased my 1960 6 cyl I discovered that the head threads appeared to be considerably longer than for the suggested J8. With blue print copy in hand I determined that an "L" length plug would use all the thread available. Comparing the heat ranges, I found that the L89 plug would work. I had those in stock as an L89CM (moped.) They have been in the engine since 1985! Wish they would wear out so I could use RL89. I have solid wires and the radio goes "ticky, ticky." But who needs a radio? So, It might be suggested to check the thread length in the 259 head. A plug thread longer than the head thread would of course be a NO,NO! But the main suggestion here is t\hat in 1955 the Champion plug called for was H11 (H12 for slow driving or oil fouling.) In 1960 the plug called for was H14Y Note that yes, now they call for a H18YC. The company (or companies) has assumed that by this time the engines are worn out. They don't take into account that some might be in excellent restored condition, or even modified to run hotter. So, if the thread length is proper for the "H" length plug, the H10 and H12 are still available. At this point I believe the H18YC may not. BUT, according to that secret heat range chart the H12 and H18YC are about the same. I have been out of business for 7 years, so I don't really know if there is an RH10 or RH12. Resistor plugs are nice but absolutely unnecessary. Just be certain that the end of the plug doesn't hit the top of the piston!! Hope this helps. ...It confused me. . Larry Blyly