No offense to anyones input on this thread or the one I have in post above but why do we have so much conflicting info on what plugs to use? Im not saying anyone is wrong, im just trying to understand it all better so I can make a more educated decision on which plugs to run.
Ok, so for the IT plugs, the higher the number, the colder the plug and the more heat the plug can channel out of the combustion chamber and to the cylinder head where it is handled by the cooling system. While that is a desirable effect, we cant ignore that we need the plug to get hot enough that it burns off fuel and stays clean.
Now, Denso recomends that for every 75-100hp added to stock you can go one step colder. If a stock car runs 380rwhp and the stock plug is an IT 16 that would mean we want to switch to an IT 20 (their next coldest plug) when we hit 450-475rwhp or so and then to IT 22's when we hit 530rwhp or so and then to IT 24's at around 600rwhp. Now, most people report 575+ rwhp at 17psi so you would be on the boarderline between IT22's and IT24's by my estimation.
The Lightning is different but many have been going too cold. Do not go too cold for your application as this will hurt you on the bottom end. The thing with the Denso's are they are not a very strong plug so if you are going to run at 110mph or more for long periods of time, run the colder plug.