tuning questiion

[XfireZ51]

Paul,

Its 41-602. BTW, here's a really cool site for plug x-reference.

http://www.sparkplug-crossreference.com/ Converts the numbers for you.

The 41-602 crosses to an NGK 6 or 7. I tried the 7 and found them a bit too cold for my motor. The 6 works very well. Another alternative is the Autolite 3923. I use the NGKs because of their heat range bracketing. I MAY get some KR at torque peak (4500-5000rpm)but it usually lasts for 1-2 frames(17frames/sec) of the datalog. I had WOT timing up around 34d at 7000rpm on the dyno and got no detonation w them. In any case I would rather foul a plug than hole a piston. Give those shot.

[mike100]

I have never deviated more than one heat range from 'stock' (if known) for any particular engine incl mild street supercharged applications.

The one time I got some free plugs that were 3 or 4 heat ranges colder that I threw into a tpi 305 camaro, it immediately failed to meet the max allowed hydrocarbons on the two speed idle emissions test that we used to use here. (I worked at a shop and we had the 4-gas bar-90 machine). It idled fine, ran fine, ...just ran dirty at idle loads.

if you don't run catalysts, I suppose it doesn't much matter.