[Dajerseyrat]

I have a 302 equipped with SVO Aluminum heads (GT40X) and I installed a set of stock replacement mustang 5.0 plugs gapped to .052 The car runs ok but idles like crap. It does sound like it has a slight misfire at idle at times and just does not seem to have the power it should. The plugs are clean when I take them out,very clean...All of them..So its not fouling out.

Then I come to find out that there is a completely different part number and plug for the aluminum GT40 heads. do you think failure to use the correct plugs is my issue?

I also suspect the wires being the culprit, cause it was the first set of wires I crimped myself and was unsure of myself...

[DanielC]

Put the correct plugs in the engine.

Go buy an OEM spark plug wire set, and put it on.
Then if you still have problems, report back.

[Irelands child]

What ignition system are you running? While the stock gap .052-.054 may be fine for a computer controlled car, not necessarily will it be right for a conventional distributor (Dura Spark, MSD or similar) I just took mine down to .045 from the .054 and it does run smoother. Also - the stock plug if it's still pure white after a number of miles may denote either a way too lean carb, timing too far advanced or that the stock, possibly an AWSF32 or similar, plug range is too hot for aluminum heads. Then there is the plug brand - I'm using NSK now instead of the original Motorcraft/Autolites and are doing well but Champions no longer seem to work well nor do Accel's in most Fords.

Plug wires - unless you broke the inner core, they should be fine if you followed the "directions" we gave you a while back.

[cobalt327]

Originally Posted by Dajerseyrat

I have a 302 equipped with SVO Aluminum heads (GT40X) and I installed a set of stock replacement mustang 5.0 plugs gapped to .052 The car runs ok but idles like crap. It does sound like it has a slight misfire at idle at times and just does not seem to have the power it should. The plugs are clean when I take them out,very clean...All of them..So its not fouling out.

Then I come to find out that there is a completely different part number and plug for the aluminum GT40 heads. do you think failure to use the correct plugs is my issue?

I also suspect the wires being the culprit, cause it was the first set of wires I crimped myself and was unsure of myself...

The stock iron head plugs like 25's are 1/4" too short- so yes they could be causing the bad idle. Do not run them any more than absolutely necessary, the exposed threads of the head will be filling up w/carbon and could- given enough time- make installing the longer 764's (or whatever you end up choosing) hard to install.

Do not forget to use antiseize on the threads and remove the plugs w/the engine cooled off, not hot.

[Dajerseyrat]

I put the correct (longer plugs) in just now..Problem solved....I am truely a *********...PS gapped to .052 idles nice even with the cam. Now just a few bugs to work out in the tune.