New Spark plug recommendation

[BamSHO]

Well since FMC discontinued the SP542 plugs, I thought the SP578 was the correct one, since the number supercedes the SP542. Come to find out that I should running M-12405-35T. Which is basically the plugs for the FORD GT with the EcoBoost motor. From what I was told that the 542s where fouling out.

I'll see how the 578s working for now, then switch over. The 578s are colder than the 534s I was running.

Oh here are the 534s I pulled out, I put new plugs in when I switched tuners. I had some gap growth of .007. Plugs where gapped at .026. I had the same growth when running Livernois tunes.

First pic is cylinders 1, 2, 3. Second is cylinders 4, 5, 6.


Yes I was told I didn't drive my car very angrily. Haha

 

[Zpak]

I believe if the past couple minutes of reading are correct, the 578’s are a heat range hotter than the 542’s.

 

[BamSHO]

Yes, but colder than the 534s. From what was related to me, the GT plug and 578 have a more narrower tip than the 542s. This was related to me from Matt at GH.

 

[Zpak]

Oh right on. Cool

 

[Raging Bull]

So we should run the 578’s Gap .027 ? Or ?

 

[yaycandy]

I see alot of growth with 534s so i just check and adjust gap at every oil change.

 

[BamSHO]

So we should run the 578’s Gap .027 ? Or ?

Yes keep the same gap. I always change plugs in the spring, no matter the mileage. Cheap insurance.

 

[FiveLeeter918]

We utilize the M-12405-35T gapped to 0.026" for all of our power packs. I personally wasn't happy with the results for the SP-578 for it to be considered a replacement for the SP542...

 

[SM105K]

We utilize the M-12405-35T gapped to 0.026" for all of our power packs. I personally wasn't happy with the results for the SP-578 for it to be considered a replacement for the SP542...

I concur. I was not a fan.

 

[15SHOPP]

I concur. I was not a fan.

How so? What didn’t you like about them?

 

[FiveLeeter918]

How so? What didn’t you like about them?

Car couldn't sustain the same spark and boost that we did on the SP-542, led to KR which reduced power output. The plugs aren't cold enough to prevent detonation.

 

[Zpak]

I wonder if plugs wearing is why I’m seeing some KR lately. Only about 16K on 542’s but...

 

[luigisho]

I wonder if plugs wearing is why I’m seeing some KR lately. Only about 16K on 542’s but...

Not alot of miles but if they don't perform as needed..

 

[SM105K]

Car couldn't sustain the same spark and boost that we did on the SP-542, led to KR which reduced power output. The plugs aren't cold enough to prevent detonation.

I even noticed that in the my logs too. Same tank of fuel and similar weather and temp conditions.

 

[15SHOPP]

Thanks for sharing!

 

[Knight]

SP-542s are still available on eBay if you look around, although they are getting progressively more difficult to find.

Hope to keep this car for some time and stocked up on a few sets. Nothing against the 578s but I'd rather stick to something with a track record.

 

[FiveLeeter918]

SP-542s are still available on eBay if you look around, although they are getting progressively more difficult to find.

Hope to keep this car for some time and stocked up on a few sets. Nothing against the 578s but I'd rather stick to something with a track record.

The M-12405-35T is working very well and they are actually cheaper than the 542s were/are

 

[Zpak]

Just be cautious about eBay and Amazon motorcraft stuff. Lots of fakes out there.

 

[Knight]

The M-12405-35T is working very well and they are actually cheaper than the 542s were/are

Nice option. Price is roughly the same to what I paid for the 542s. I would run these over the 578s.

Would you still gap them down to 0.28" or keep things the way they come (0.31")?

Just be cautious about eBay and Amazon motorcraft stuff. Lots of fakes out there.

Good point and great video. I purchased from AutoZone, Rock Auto and eBay. Every plug is checked out to make sure everything matches.

 

[FiveLeeter918]

Nice option. Price is roughly the same to what I paid for the 542s. I would run these over the 578s.

Would you still gap them down to 0.28" or keep things the way they come (0.31")?



Good point and great video. I purchased from AutoZone, Rock Auto and eBay. Every plug is checked out to make sure everything matches.

I run mine at 0.026" but will all depend on your tuner's recommendations.