I've been searching and reading and found all recommendations for all kinds of plugs, but really no reviews on what performs good or what doesn't. On a N/A GT with basic bolt ons and diablo tuned, is it worth going -1 colder than stock? What is the benefit/s of doing this? What gap? Let's say it's time to do the plugs (50,000 miles) so we are not just wasting money for fun. Any benefit in doing new wires? I've heard of the autolite 103, the ngk's... Really, what is the benefit of going colder and re-gaping to other over stock in a N/A 99-04 GT?
Now, my friend used one of those "engine" cleaners, the one you pour before doing the oil change, and it's supposed to loosen all kinds of crap inside the engine to flush with the oil... Is it safe in our engines? If so, how often should it be done?
Thanks for all your input, I'm still learning on the Mustangs...

 

If you have a 2004 GT, you don't have any plug wires. Instead, you have coils which sit right on top of your plugs. Leave those alone....the stock ones are fine. Wires went away in 1999 on a Mustang GT.

As for plugs, one-stage colder is better then stock. A plug heat range is determined by the insulator. Colder plugs will decreaes the temperature in your combustion chamber which will improve performce a tad and prevent detonation. If you go too cold, you won't burn-off all the carbon and get deposits. Ford runs the hotter plugs for emissions reasons.

Keep the gap at stock setting which I think is 54 (but I am not sure) unless you have nitrous, turbo, or a super charger. You should not increase the gap unless you have ignition upgrades which are pointless on a stock Mustang.

As far as agressive engine cleaners.....do you have carbon build-up? Probably not especially with stock heat range plugs. I think people just like to spend their money on voodo. Something sounds good, so they do it.

I can guarentee you that you won't find one experienced drag racer with a fast Mustang using this stuff.

 

Thanks, I meant coils... So one step colder it's better on these engines. I will go out now and by either of the ones available at my local shop. Prob the autolite 103. Just checked my plugs and they need to go.

 

Advanced auto gave me autolite 5245 saying that these replace the 103. Before I start working on the car, is this right?

 

I am not sure about that. I use the 103's and were nopt aware that they changed. The 103's are copper BTW.

 

I called autolite and they told me that the ones advanced gave me are 2 stages hotter than my stock 104! I went back to the store and gave them hell about it. The excuse was that the guy that sold me the stuff is a weekend part-time. I finally got 103 from autozone. Thanks.

 

That's what you get for $8/hr.

This is why it is always best to come to a place like this to ask these questions and then tell the parts guy what you want.

That would have sucked had you installed those plugs.

 

I got them installed. Now I'm going back to return the torque wrench and extension, just to **** them off a little more....
My old plugs look like crap compared to the new ones. It was time! Thanks.

 

How many miles on them?

 

49,000. They have no core in comparison to the new ones. The old ones are stock motorcraft.

 

the platinum tipped stockers have a very small electrode. Mine crapped out suddenly and vigorously at 65k. copper plugs may not last near as long but they're sure a helluva lot cheaper and changing them about every 15K miles gives you some insight into what's happening inside your motor as time goes on.

The dumbest thing car makers ever did was increase time-between-maintenance all over the place. That's the kind of thing that turns little problems into giant motor-blowing catastrophies.

EDIT: Good job coming back and confirming those plugs. You might have had a bad time otherwise.

 

It was just too odd for me that the "cross reference" was the "exact" plug. When I went to autolite's website, the 103's are used for 03-04 Cobras as stated in their application guide along with a bunch of GM cars. The 5245 were for the same cars except any Ford! That's when I decided to call them and ask directly. The tech confirmed that those are 2 steps hotter than my 104 stock! I explained to him that it was recommended by the Advanced guy since his computer told him to and he asked me the store # because he believes their system is not working properly, although I knew he felt it was the guy's mistake. Imagine if I was running NOS and I had installed these as instructed by Advanced? WOW. Thanks heaven for these forums and guys like you!!!

 

In the future bro, another one step colder plug is AWSF-22C Motorcraft and Accel U groove P0514 are to steps if you go boosted. A colder plug is a blessing in a N/A mustang. I was running the autolite 103's in my 96 GT after I had the motor rebuilt and it went to an 11:8-1 compression. I am currently two stages colder and I am going to buy from Randy hopefully next payday the motorcraft plugs two steps colder. Copper plugs have more spark energy and wear out quicker, platinum is just for longevity.

 

I think my tuner has me running 103's on my car with a blower.