WETTE VETTE

I know a little about plug heat ranges and their effect on performance. For example too hot will lead to detonation and pre ignition. Too cold will cause plugs to foul out sooner and the idle will not be as clean. I normally use NGK R5671A-8 and I just tried a set of R5671A-9 plugs which are colder than the 8's. The performance seemed to be a little off with the -9's. It idled OK, but the 38 degrees locked in MSD ignition will probably idle the coldest plugs on the planet! Does anyone know if to cold of plug could cause a loss in performance? The -8's worked well and there were no signs of detonation. I wanted to try the -9's because it was my thought that the coldest possible plug that still works should be used. Maybe my thought process is a little off here. Thanks for your thoughts and experiences on this subject.

WETTE VETTE

From the NGK website I found a statement that says going one step colder within the same series of plug will reduce combustion chamber temperatures by 70 to 100 degrees C. Combustion chamber heat is critical to combustion efficiency as long as pre ignition and detonation are not encountered. Higher compression ratios make more heat due to the higher pressures and that is part of the reason higher compression motors are more efficient than lower compression motors. Now aluminum heads need more compression than iron ones on otherwise indetical motors to create the same amount of heat and therefore pressure because of the good heat dissapitation characteristics of aluminum. So if colder plugs are run and combustion chamber temps are lowered it will act like a slight drop in compression which will lower HP. How much?????? Probably not a lot. It blows my theory about running the coldest plugs you can run without fouling. I ran -8's and had no detonation or preignition probs and they idled cleanly. Going to the -9's is probably a bad idea. These plugs will foul out before the dash 8's and will cost me some HP. Here is one more interesting finding. When leaning out a motor in search of max HP you must cater to the leanest cylinders so as to keep them out of detonation right. Well some drag racers will identify the leanest cyls through spark plug reading and will install colder plugs in those cylinders. Then they run the motor and can normally lean the motor out a few more jet sizes. Basically the colder plugs make the lean cyls less efficient and they now match the rest and more fuel can be pulled which will add up some more HP. This was a trick commonly done in small block chevys before intake manifold design made nearly all cyls receive equal A/F. Pretty cool. Just a note NGK recommends -8 plugs for the 800SC, 600SC, and 575SC and -9's for the 900SC. I think I will go back to the -8's.