NGK R5671a-8

-8 heat range is what I use for a 300 shot of nitrous. As said above; too cold.

NGK heat range scale is oppoaite of Champion and Autolite. A typical pump gas streeter uses a 4 or 5 heat range plug. If it was mine and the compression was marginal for pump 91 I would start with a NGK projected tip in the -6 range. If you need a pn let us know.

As a point of reference, stock NGK heat range is 5, projected tip.

I run a 7 non projected tip on a 175hp shot of nitrous and 28-29 deg total advance

I have had faulty Autolites and Champion plugs OOTB. So far I have yet to see a NGK plug DOA.