NGK (7397) TR5IX Iridium IX Spark Plug, Pack of 1

Comment: These replace the former NGK part TR55 iridium spark plugs. Not sure of what the difference is, but I suspect it is slight. Installed 8 of these gapped at 0.040" on a 2004 Pontiac GTO, along with 8.5mm MSD wires (generic LS1 kit) and K&N Cold Air Intake kit (57-3044). The car was formerly throwing engine codes of right and left banks running lean/rich. New plugs and wires cleared that code. I've read on forums that the TR5IX plugs show a 5HP gain over stock plugs if your car is already modded, but may be only as good as stock plugs if the car is stock otherwise. Car is perhaps a slight bit more responsive, but I think that is due to clearing the engine code and letting the engine relearn itself. Removing stock wires on an LS1 is a ridiculous job (you just have to rip them out), so that added time to the whole job. Plugs and wires took 3 hours (yes, I know, that is retarded long), but the new MSD wires have a much longer boot on them which will facilitate easy extraction - the stock boots are nearly buried in the LS1's plug head shields, so there's not much to grab. Changed mine at 80K miles. Seems to have helped the car overall, however no improvement in MPG. Worth the money if you're going to mod the car further, or just want to be able to say you have NGK iridium plugs (stocker AC Delco plugs are iridium as well). Overall, installing the plugs is easy as long as you have a spark plug socket with a universal joint. Recommended for every LS1 Goat.