Another Spark Plug Question

[Glenn B.]

I've searched previous posts and believe that an R45XLS is the optimal plug for my stock 67 427-290. I am however running R42XLS at present.

I understand that the 45 is a hotter plug that resists fouling better. I am not seeing any fouling issues at this point.

Would my engine be expected to behave/run any differently with a 45 plug Vs the current 42 plug?

Thanks

[Duke W.]

Re: Another Spark Plug Question

As long as heat range 2, which is one range colder than OE (and most even consider OE heat range 3 too cold for normal driving) don't misfire from fouling, heat range 5 will not result in different operational characteristics.

But the next time you change plugs, consider a hotter heat range, especially if the existing plugs have a lot of deposit buildup on the insulator, even if there is no misfire.

The plugs could be fouled right now and you don't even know it. A fouled plug can work fine until you go to WOT and high revs where it can misfire.

Duke

[Glenn B.]

Re: Another Spark Plug Question

Hi Duke, I could not see any near term benefity from swapping out the current plugs.

I sampled 2 plkugs, and they show only a very modest amount of tan colored deposit - which I believe is considered normal. But I will put in R45's when current set is ready for retirement.

Thanks again for your advice on the distributor. - now have all mechanical advance in (30 deg) by 3500RPM - performance is improved.