spark plug selection

Looking for spark plug suggestions I now run ngk R5671A-7 plugs. Engine is 557 tfs streets flat tops .738 lift cam 34* timing block decked to 0. Am I in the correct range ? go hotter? go colder? car runs on c-12 race gas.

I suspect that a "8" would be better per your application.
"""""""""""""""""" "9" would not be an issue.

Thanks Lem the 7's seem want to foul easily. EGT's are around 1380*, tryed to jet up to 94's but engine would not want to rev. Went to 90's car picked up but egts also went close to 1400.

The "7" is warm for your application.......they should not be fouling. Maybe the idle circuit is rich or weak ignition?

I had my numbers crossed up I thought a 7 was on the cold end on an ngk. The plugs could have gotten fouled when the carb had powervalves and overjetted. I was having so many other issues with the car that I never took the time to change the plugs after some major carb tuning and going from c-16 fuel to c-12. I have two new sets of autolite ar3933 that I found in one of the cabinets in the shop. They were for a friends 427 small block that I built a while back. They are two steps colder then the ngk 7. Any suggestion on optimum gap?

The side gaped AR3933 do not require a lot of gap...... .025"ish will work.

BUZZ BUZZARD wrote:I had my numbers crossed up I thought a 7 was on the cold end on an ngk. The plugs could have gotten fouled when the carb had powervalves and overjetted. I was having so many other issues with the car that I never took the time to change the plugs after some major carb tuning and going from c-16 fuel to c-12. I have two new sets of autolite ar3933 that I found in one of the cabinets in the shop. They were for a friends 427 small block that I built a while back. They are two steps colder then the ngk 7. Any suggestion on optimum gap?

The Jap plugs are backwards.......bigger # = colder.

Champion and Autolite.....bigger # = hotter.

Thanks for the info.