Spark Plugs - PI H/C/I swap

sk8erord · Oct 28, 2018

Hi guys. I did some searching and found a few different threads from several years ago, but I wanted to get some fresh(er) opinions. When I bought my car, it had Autolite 104s in it. They were brand new because the owner had been trying to diagnose a misfire. Turned out to be a bent valve, so it went away when I did the headswap.

Anyways, after I finished the swap and ran it a few times, I bought the Motorcraft SP432 plugs for it since I didn't really know how new his plugs were and a lot of people recommended them. However, the car seems to run worse with them than the autolite 104s. Maybe it's gap, I don't know, but it definitely takes longer to start, and feels a little more sluggish (but that could be imagination - the starting however, is definite).

So... thoughts? Go back to Autolite 104s? Get something a step colder? I know the compression is higher now that I've done the PI headswap, so would a colder plug benefit me? Should I get a more "premium" plug like NGK?

01yellercobra · Oct 28, 2018

What gap are you running? Has it been acting like this since the swap?

sk8erord · Oct 29, 2018

01yellercobra said:
What gap are you running? Has it been acting like this since the swap?

Stock gap - .054. It started immediately after swapping to the Motorcraft plugs. I initially started up the engine after the headswap and ran it for a bit with the autolites that were in there. I did not verify the gap on those as I had planned to swap them.

01yellercobra · Oct 29, 2018

I'd say all signs point towards the plugs then. Its possible to get bad plugs out of the box. I'd throw the Autolites back in and see what happens.

sk8erord · Oct 30, 2018

Yeah, I kind of figured that - I guess what I'm fishing for is if anyone has noticed a benefit from going away from the stock temp plug at my level of mods. I know on my turbo'd vehicles, my tuners have me put in 1 step colder plugs when they turn up the boost, so I was curious if higher compression in this engine would warrant the same response, along with a gapping change.

07GtS197 · Oct 30, 2018

Youre compression ratio is only about 1 point higher than stock so I doubt having the stock heat range plugs is causing this. I know they say usually the last thing you did is what is the problem but I find it hard to believe plugs will cause hard starting. Now what 01yellercobra could be onto something. I once bought oem plugs for my 07 gt and installed them only to have it run like shit and miss. I pulled the plugs and noticed the porcelain insulator was loose. Maybe it was just a bad batch but it left a bad taste in my mouth so I dont use their plugs in that car anymore.

Edid: I just did some research and it looks like the 104s are copper, I doubt that going from copper to platinum would be a huge difference but I speculate that is the issue. You could always try them and see how it runs. Theyre easy enough to change.

sk8erord · Oct 30, 2018

I apologize, I could have worded this better - I basically have 2 questions:

1. Has anyone seen this with the motorcraft plugs. Clearly the car likes the autolites better for whatever reason. It was the only change I made, and the difference in time it took the car to turn over was obvious on the first startup after the plug swap. (And I have a brand new starter, I changed it during the headswap). So I'm going to likely go back to Autolites unless...

2. Since I'm going to change plugs anyways, is there a benefit to a colder temp range. I don't believe the temp range is the issue, since it ran fine on the 104s, which are a stock temp range, but I'm asking IF anyone has seen any benefits or has any good reasons to go colder and/or a different gap. If not, I'll go back to just 104s.