Dont use nova plugs in os based engines, just don’t do it. U cause the threads to get sloppy as cause air leaks, the deck hieghts are different it’s like using a metric screw when the car uses standard, no different.

If u need a plug that is perfect in a novarossi go get some O’Donnell plugs, they follow a more nova design.

In os engines u can use the p3 pretty much anytime anywhere and get the best results, if u can’t get them then use a #4 or #5 or even #6 if they still make them by the rebrand Kings LM (you know them as werks or the Orion engines) or formerly known as sirio #5 plugs. They rock and the 4 I would assume is even better. I actually really like these plugs and have as much confidence in a new sirio plug as a os p3 but I think the p3 longevity wins out.

U can pretty much categorize engines in two categorize, you have your os type engines and your nova type engines. A lot follow each, some say the alpha engines and arrow engines are there own catagory but if I am right didn’t arrow basically copy a vspec down to the point u could use a arrow rebuild kit in an os vspec? To me that puts them in the os catagory. Picco I used last 10 years ago used an nova style plug (I blewa lot of rods so I may have been wrong but not sure)