I have a 65 lesabre 300 4bl and a 65 skylark 300 2bl. are the heads different. The parts store is telling me the plugs are? Why is this?
Heads are the same. Plugs maybe different heat range. Probably 4 barrel motor has one step colder range due to higher compression pistons.
Let’s get the details right about this. 1) Both motors use the exact same head. 2) the 2bbl motor uses a dished piston for a reduced compression ratio. 3) it’s not the compression change up or down in and of itself that makes for the need for a different plug to be run, but it’s the HP made. Any heat range plug has about a 600 degree temperature range that it will work in. The cylinder temp can therefore be 300 degrees hotter then the middle range of the plug, or 300 degrees colder and where good. The 4 bbl motor with its higher compression and increased air flow will be making more power then the 2 bbl motor and as such needs a different plug. This could be just a colder heat range, or a plug that does not have a extended tip maybe. I do recall what a plug looks like for both motors so can’t be any more definitive then this.
