I talked to NGK last week about the what spark plugs to run on a b/blk chevy with 200 shot, they told me donot go colder than 9's. he told me that top fuelers run 11's. Also we're running 36 degrees inital, with 8 degrees retard down to 28* on the bottle and that's on a pump gas 468" motor 10.2 comp. I certainly would not run the 598 more than 34*'s inital.
JMO
Zip.