Spark Plug Gap GENERAL questions

[valkyr]

The 2010 Mazdaspeed3 manual states that the preferred gap is 0.024 -> 0.027:

2010 Mazda Speed3 Manual on page 10-4.

Question 1:
I'm curious what the history of coming up with 0.026 -> 0.028 was if anyone remembers?

I'm running mostly stock parts except for an air intake and a [apparently] a short shift plate.

Question 2:
Why do spark plug replacements come gapped so large at 0.044 when you buy replacements? Are the autoparts stores selling us the same plug that goes in the Stock Mazda 3 (non-speed 3)?

[CosmicArkie]

If you're going into the store and asking the counterman to look something up, you're taking your chances.

Know what you want and ask for it by number. Last set I got were gapped .028.

[valkyr]

Originally Posted by CosmicArkie If you're going into the store and asking the counterman to look something up, you're taking your chances.

I think most of us know that

Did you get the NGKs? They were out of the NGKs but I see on Napa those are gapped at 0.027 (damn it). I regapped mine to 0.030.

Anyone know why the Densos and autolites come gapped so large then?

[SternRitteR]

You americans with your imperial decimal places . So much easier and more accurate to say 0.7mm if your mods allow it .

[Johnasaurus]

Originally Posted by SternRitteR You americans with your imperial decimal places . So much easier and more accurate to say 0.7mm if your mods allow it .

Murcia!

If you buy stock heat range plugs gap them to stock. There's a reason they are that way. I'm no expert in the history of spark plug gap but I've never had a problem gaping them to stock specs.

[hitmeagaintubesock]

I figured out the hard way in my gen one that every thing the parts places sells is gapped wrong. I replaced plugs and I was told to gap at.051 then I had spark blow out like crazy. Done a little reading and saw that was way off. I work for a part store and sent an email to our programmers to fix the incorrect gap info. They didn't.

[DVM17]

They come gapped so large as they aren't just to cater to mazdaspeed's needs.

and .026 is the preferred gap seeing as when you go larger, boost tends to blow the spark out. hell, I'm gapped to .024 right now on stock heat range plugs and I have full bolt-ons (except for mani) and it runs great.

Now if I were getting knock, I would definitely switch out for the colder plugs I have sitting in my garage. But I saw spark blowout last time I used them.

This has been covered many times. I don't see the need for another thread about just wondering why the gap is like that. You want the gap as wide as possible to make the most power (optimized amount of spark), but there's a finite line between widest gap allowed and spark blowout. It takes a while to find the sweet spot. (at least for me)