I have noticed numeris post's about plug gapping. The sticker under my hood says to gap at .50 why are some people gapping at .42 .45 .40 ect. What affects does using a smaller or larger gap do? And should I stick to what is recommended, .50? I am pretty much stock, except for MSD Coil pack and 8.5 mm wires, K&N drop-in. Iridium plugs by NGK.

 

The bigger the gap, the better the ignition system ignites the fuel. However there is a limit. The coil can only provide so much energy to the spark plugs, the wider the gap and the higher the cylinder pressures, the more energy it takes to light the spark plugs. I would stick with the recommended plug gap as long as you are stock, unless you start experiencing "spark blowout" when under boost (You'll feel some hesitation under boost, particularly in the higher RPMS).

As you modify your car and increase boost, the spark gaps need to come down to prevent spark blowout. I'm running a gap of .030" on my SRT-4, but I have a big turbo pushing 20psi +. When I was running ~19-20psi on the stock turbo I gapped the plugs at .038"

 

I do have a hesitation under acceleration. I just figured I might have a boost leak, but, I am spiking to 15 and holding 12.5-13.5 stock. What do you think I should gap these NGK iridiums at?

 

start at .045 and adjust from there