Need help with spark plug #'s

[DAVZKAR]

I have a 91 ZR1 and I need help with spark plug #'s. I need the #'s for AC rapid fire plugs one or two heat ranges colder than stock. Can anyone help with this problem.

 

[Hib Halverson]

AC only has them one range colder than stock...but that's bit confusing because up until just before the ZR1 was released for sale in late 1989, the engine had always used the AC 1 heat range. Because of concerns with pre-delivery fouling, at the last minute, the plug was changed to an AC 2 heat range.

I believe the AC Rapid Fires for LT5 are the 8s. It is unknown what heat range plug that is.

When I used RFs, I used the 9 but appearently, the Rapid Fire line has changed much since then.

Today, I use the Denso IT-22 which is one heat range colder than stock. I have tried the IT-24 in chassis dyno tests and it works very well for that so it would be a good plug to race on, I think.

 

[DAVZKAR]

Plug#s

Hib,
Thank you for the plug #'s. I just posted on the ZR1 net. I now have new issue's altogether with rough idle and loss of power.