Hey Guys,

Just wondering how to determine the correct plugs (mainly focussed on temperature range) for the Wagon.. I'd imagine that compression may factor into the decision making process.

I'm thinking about going back to some XR6 spec plugs. The plugs I have now are extremely cold, and I dont think I'm in the correct operating temp range.

considering the work you have had done by jmm surely they would recommend some to you. no doubt they would prolly just try to sell you their autolite product though. thats not a bad compression ratio you have there i noticed. much more and youll start dieselling..

OK, here's a rule of thumb i picked up on when doing the blower install...

The world according to Americans:

Reduce the gap by 0.004" for every 6.25hp increase per cylinder....

So, for a V8, reduce the gap by 0.004" for every (6.25*8) 50hp increase and for a 6 cylinder, reduce the gap by 0.004" for every 37.5hp increase.

Of course this gets thrown out the window with aftermarket spark, if running MSD or similar, open up calculated gap by 0.002" - 0.005"

No idea what the theories are based on - I only knows whats I hears...

JMM doesnt ship their gear out with compression ratio's as high as mine.. so I'm not sure whether I should be looking at plugs in a different way due to the high compression.

I should pop it up to 20:1 and see if it will run on diesel ey

fuel injected cars don't 'diesel' . when you trun the key off you turn the fuel off too. if your injected car does do it you have injector problems.


back to the plugs. the rule of themb is the 'hotter' (more modded) the engine the colder the plug.
but it also comes down to what works for you.
for your engine i'd start with the XR6 plug, and try colder and colder plugs untill you run into problem like fouling and missing.

my XR6 is almost stock and i use denso 20 heat range. that is 2 colder than stock falcon and that fixed the miss fire and detonation at high revs in 3rd.

just buy some and see what work.