Contour Enthusiasts Group Archives Forums Modifications Duratec Performance NGK Iridium plugs

You already know you are!!!

NGK made a nice difference in my Impulse!

I wish I had 35 degrees the other day. It was 10 degrees and the wind was blowing. Dumba$$ me though for waiting until it got cold to change them.

The ground on the Denso Iridium plug is nickel and will only bee good for 12kk miles on three of our cylinders. What's the ground material in the NGK?

It seems that the Bosch +4's are hit or miss. I have them in mine. When i installed them, I had single electrode FMS plugs with about 20+k on them so naturally they felt better. One thing that has not really been discussed is hot or cold plugs for different burns. Anyone care to comment of advantages or disadvantages to running a hotter or colder plug vs. stock.

Get the same plugs I told Timmay to get. Autolite Platinum Pro APP764. Double plats are the way to go with our ignition system. Something like $4 a piece. Gap is .054

Thanks, any thoughts on different plug temps. Love the sig.


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How can you guys make the determination that the plugs are bad? (other than they look worn/eroded).
My wife's 96 Duratec has about 35K on the Bosch +4s. The engine idles so smoothly, that you can't even tell that its running. Accelerates well too.
I've read a lot of Bosch bashing here, but have had an OK experience w/mine.
I changed the original plugs at 50K. All still looked fairly good, except for the front ones from each bank, which were eroded much worse than the others.
On a similar subject, I believe Hot Rod magazine dyno'd plug wires and found all were pretty much the same too.

At 25k miles on my SVT now, it misfires at idle. Performance is down just slightly. I haven't pulled a plug, but I planned to change them in the Spring. If you don't notice a performance or fuel economy issue, then don't bother checking the plugs. Most issues with new plugs is the gap. Since +4's come pre gapped, no one bothers to check them (and they are hard to adjust anyway). No one can talk away your experience so use what works for you.

I've been looking around for colder plugs for our application. Dyno guy turned me on to that overlooked detail in my 11.2:1 compression motor as a possible fix for my knock/timing problems.

Here's what I've learned about heat ranges: a colder plug will cool faster, thus preventing pre-ignition caused by an overheated plug at high throttle. However, its operating temp will be lower, and if this goes too low it will tend to foul as it will not clean deposits from the air/fuel charge and combustion at low throttle settings. Unless you are bumping compression or chasing a knock problem (like some people have seen on the +4's), there should be no need for a colder plug in our motors.

The specs on our plugs (from autolite.com for APP764): 14mm thread dia, .708" reach, 5/8" hex head, tapered seat, power tip, D14 heat range (dunno if D14 is some sort of standard or and Autolite reference).

OK, so I looked around and found a big Excel cross reference sheet for all spark plug mfg'ers. a little old, but it did have the AP764 listed. As far as I can tell, the plug spec'ed on the Duratech (both 2.5 and 3.0) is the coldest standard part offered by the plug companies in that form factor.

NGK appears to offer a racing plug (called a street/strip use plug) that may be colder, but it is not platinum, it is a nickel electrode plug. I'd have to change them every 12k or so. Not sure if I want to get into that or not.

Another thing I've learned is that higher compression requires smaller gap, so I'm going to try something a little smaller than .054". Any suggestions?

I emailed NGK and Autolite looking for a colder plug than what they call out for the Duratech, but no answers yet. Any spark plug/engine gurus have some help for me?