I did not think this too advanced put got no response in LT1 tech. I cross referenced the AFR plug number for my heads to a NGK part # R5672A-9. I ordered the plugs thinking I was all set. The plugs turned out to be non-resistor type plugs and I am worried I should not use them with the stock ECM. I can match the sizing spec in a resistor type plug but I am confused about the heat range. I thought the -9 meant this part was heat range 9 which I thought cold but matched AFR spec. If I look in the NGK catalog for anything colder then heat range 7 the prices get very high and the choices very slim. To make matters worse I am planning on spraying nitrous by the end of summer. Intake fuel rail is being modified for the NOS noszles and I thought to spray 175 to get a handle on things. Eventually either last thing this summer or next spring I will spray 300. I was hoping to only go one range colder at the 300 or not change at all. This car is not used on the street. Can anyone help or recommend a specific plug?

 

I had the same question last year and got ahold of an NGK rep. I have a supercharged afr head TA with 500 plus rwhp and have been using non resistor plugs for a year no problems, what I was told is as long as I used resistor wires it was ok to use non resistor plugs.

John Carpico