Spark Plugs

What brand and heat range plugs are you guys using for High boost over 25 psi.

I have an early set of the original GN1 race heads which had some of the worst threads. So I had the spark plugs holes heli- coiled. Now I have to run the gasketed spark plugs and not the tapered seat plugs.

Here is what I have found for the gasketed plugs.

FR2LS stock AC Delco
FR1LS 1 colder AC delco


Autolite
3922 1colder
3923 stock
AR 3933 2 colders big boost clip gapped

Anybody using NGK's have the correct number for the gasketed spark plugs.

Thanks
Steve C

[The Radius Kid]

I'm curious as to why Champion spec's tapered seat plugs in the first place?I was up getting my GN-1's flowed after porting and the head porter said he thought they should be gasketed.Every aluminum head I've seen uses gasketed plugs.What gives?

[STG2LTD]

Hi Steve, Glad you brought this topic up.

I have an early set of 14bolt GN1's that were cut for a gasket (washer) type plug. All the other GN1's i've seen accept the tapered plug ala (autolight 103's).

The plug's i'm currently running are autolight 3924's.
Currently i'm having misfiring problems under higher boost 22-26psi.

Hopefully we'll get some more insight from other board members.

Thanks for posting the other plug #'s. I think i'll give the 3922's a try.

I'm hoping Cal Hartline will jump in here, he might have some insight on the early version of these heads, and what works best.

Jason Hall

[EightSecV6]

I had a set of the early GN1's as well, I believe they were stamped 006, They took tapered seat plugs as well as all stage 2 heads (with the exception of the 10 mm Indy heads). The 3922(washer seat) is an exc. plug for high boost race applications but it will not live long in a street engine because it is too cold and eventually begin to misfire(fouls).Run the gap at a tight .030.

[The Radius Kid]

So,could you not sub in a hotter range plug for the street?Maybe something equivalent to a Autolite 104 with a gasket?

[EightSecV6]

That would be the 3924