Alright guy's 528 indy headed what heat range plug would y'all use with a ngk plug naturally aspirated. We are getting stingy, so far we 1.36 60 ft. I'am going to start shock setting changes this weekend to see if sixty foot will improve. WE are still foot braking at 2800 rpm, at 2911lbs. Any help will be appreciated. Thanks Brian W.

Depends on your compression. Mine is 11.5 and I run Autolite AR3911's.

I use to run champion c-59's in -1's Now run NGK's 5671-11's In 13.1 flattop motor.

Mancini Racing has a chart on their website and Indy has a chart in their catalog. Indy recommends the Champion racing plugs with the super short ground strap. That is what I started to use and they seem to work just fine.

AR 3933 for a 13:1+ on alky, and AR3934 for milder 11-12:1 engine on race fuel.

5671-8 on alcohol works great

Compression is 11.5 to 1 flat top piston and using 110 race fuel.Thanks for the help. Brian W.

I have run the NGK R5672A-8's for a long time now and I can get them at advance for 2bucks a piece.
I am 12.8:1.

Autolite racing AR3934 I get several seasons out of a set, and I change them out..But to be honest there is probably not much wrong with them.

Most of you guys must not be able to read. He ask for NGK numbers not Autolite not Champion. NGK 5671A-8
I get so sick of the guys that want to tell you about everything but what you ask about. Maybe there is a reason he ask about NGK. If you can't input anything about the asked question don't input anything. If you don't like my responce tuff shi$.