[usc335]

UPDATE (4/2/10): I tried the HKS plugs but they resulted in cold start misfires (and I live in Southern California). The car would start, but would misfire. It took 3 to 4 starts before the misfires cleared up. After that, the car ran great and didn't recur until after the car was shut off for several hours (over 4 hours). I switched back to new stock plugs and the misfires went away. It appears, at least on my car, that 2 steps colder plugs are too cold.
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UPDATE (2/20/10): Added ceramic insulator diameter comparison to Stock (item 1a) -- they are the same diameter. I just got a set of XL heat range 8 plugs (two step colder than stock) and I am going to try them out after modifying a 16mm or 5/8in socket.
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I contacted HKS USA about their Iridium spark plugs and here is what they had to say:

(1) According to HKS Japan, the "XL" series (50003-M40XL, heat range 8 & 50003-M45XL, heat range 9) are compatible with the 07+ 335i & 135i (N54 engine). HKS Japan's website lists the "XL" for the 335:
http://www.hks-power.co.jp/products/...st/pdf/bmw.pdf
"XL" requires a 16mm socket (the ceramic insulator diameter is 10.4mm)
=> It looks like a custom spark plug wrench needs to be fabricated to use the "XL" Plugs...

(1a) HKS XL vs. STOCK (Note: the ceramic insulator diameters are the same):







(2) Below is a link to someone’s blog (in Japanese) showing an "XL" spark plug being installed on a 335i (too bad I can't read Japanese!).
http://cayman01.exblog.jp/tags/HKS%E...R+FIRE+RACING/

(3) The "XL" spark plugs are also used for the EVO X & Genesis Coupe 3.8L V6.
http://www.hksusa.com/products/?id=3115

(4) The "HL" series (50003-M40HL, heat range 8 & 50003-M45HL, heat range 9) can be physically installed, but it may leak due to the ceramic insulator diameter being smaller than the stock & "XL" insulator. Please see the attached picture comparing the "HL" and "XL" insulator size. Because of this, it is not recommended to use "HL" series plugs on a N54 engine.
"HL" requires a 14mm socket (the ceramic insulator diameter is 9mm)

Let me make myself clear, the GTR plugs are "HL Series" and are NOT recommended for the N54. However, the "XL Series" ARE compatible.

(5) You can purchase them from any authorized HKS dealer or directly from the HKS USA website.
http://www.hksusa.com/products/?id=3115

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The latest thread on the HKS Plugs is here:
http://www.e90post.com/forums/showthread.php?t=350416
Here are some more:
http://www.e90post.com/forums/showthread.php?t=272511
http://www.e90post.com/forums/showthread.php?t=332543
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No, I haven't tried these on my car... yet.

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Stock Spark Plug Data Courtesy of Former Boosted IS:

ZGR6STE2 Bosch Super Plus Spark Plug
12mm Thread Size, 26.5mm (1.04") Reach, 9/16" (14.3mm) Bi-Hex Size, Gasket Seat, Interference Suppression Resistor, Surface Gap Plug, 3 Binary Ground Electrodes, Nickel-Yttrium Center Electrode, Solid Terminal Nut, 0.027" (0.7mm) Gap, Heat Range 6

[BuLoOoSki]

here is a translation of the page in Japanese, used google translation so its not perfect.

http://translate.google.com.kw/trans...ial%26hs%3DTdz

[enrita]

great info ! thanks!

[KWY91]

Nice find, thanks!

[dlbrooks18]

Originally Posted by M3_Kidracer

Nice find, thanks!

+1.. subscribed for your testing results

[hun77777]

so what's the stock spark plug heat range? is 9 better than 8?

[Former_Boosted_IS]

Can we VERIFY what heat range our stock plugs are? Second, can we verify that these are 14mm so we can use the stock thin wall socket to install them.

[KWY91]

Just want to add a slightly OT question, when is the best time to consider a spark plug upgrade? Currently almost hitting 10,000 km on my car

Cheers!

[enrita]

Originally Posted by Former_Boosted_IS

Can we VERIFY what heat range our stock plugs are? Second, can we verify that these are 14mm so we can use the stock thin wall socket to install them.

those are not 14mm. probably 16mm. One guy is running them from n54tech and he had to modify them to fit 14mm. Stock are the plugs 6 grade.
found this with specs: http://www.hks-power.co.jp/db/produc...LN=EN&N_ID=326

[Former_Boosted_IS]

I did verify the heat range on our plugs 6.

ZGR6STE2 Bosch Super Plus Spark Plug
12mm Thread Size, 26.5mm (1.04") Reach, 9/16" (14.3mm) Bi-Hex Size, Gasket Seat, Interference Suppression Resistor, Surface Gap Plug, 3 Binary Ground Electrodes, Nickel-Yttrium Center Electrode, Solid Terminal Nut, .027" (0.7mm) Gap, Heat Range 6

[Former_Boosted_IS]

Originally Posted by enrita

those are not 14mm. probably 16mm. One guy is running them from n54tech and he had to modify them to fit 14mm. Stock are the plugs 6 grade.
found this with specs: http://www.hks-power.co.jp/db/produc...LN=EN&N_ID=326

Ah great. So that is the plug we need, but the wrong size socket?

[Former_Boosted_IS]

USC, can you please see if HKS can make the 50003-M40XL and 50003-M45XL in a 14mm size?

[enrita]

Originally Posted by Former_Boosted_IS

Ah great. So that is the plug we need, but the wrong size socket?

yeah apparently. Will see. I think i will give the GTR a go anyway. I got leakage on the stock ones as well so i guess it wont harm.

[enrita]

for the insulator is it meant the white part with 3 black stripes? if yes i can say that both Stock and HL / GTR ones have the exact same size of that.

[hun77777]

so the one with heat range 8 is two step colder and one with heat range 9 is three step colder? that seems quite a difference to me...

[usc335]

I just added the following to the first post:
Wrench Sizes:
"XL" requires a 16mm socket (the ceramic insulator diameter is 10.5mm)
"HL" requires a 14mm socket (the ceramic insulator diameter is 9mm)
=> It looks like a custom spark plug wrench needs to be fabricated to use the "XL" Plugs...

and HKS Japan's website lists the "XL"for the 335:
http://www.hks-power.co.jp/products/...st/pdf/bmw.pdf

[dlbrooks18]

so now I'm confused, so do we have colder plugs that fit or not? this seems like a worthy mod, but very risky

[hun77777]

so if i were to put XL series on my car, since its heat range is 9 will there be any significant risk factor at all? it's not one step, not two, it's 3 step colder than stock range of 6...

[enrita]

Best is to use the one with heat range 8 , not 9 . 2 step colder is enough .

[Htown09]

Originally Posted by enrita

Best is to use the one with heat range 8 , not 9 . 2 step colder is enough .

[B]The GTR is a 8, which is two steps colder and if you have mods the one you need.

50003-M40HL NISSAN Skyline GT-R 2009 ; R35 8

It is the 6th one from the bottom. One member already has these installed and he says it works fine. If I can find a wrench I will order these and get them installed. There will be no modifying the hex on these just get a 14mm wrench. /B]

[Htown09]

Originally Posted by dlbrooks18

so now I'm confused, so do we have colder plugs that fit or not? this seems like a worthy mod, but very risky

Just order 50003-M40HL NISSAN Skyline GT-R 2009 ; R35 8 and find a 14mm wrench and install them. You might have to regap them.

Is anyone else having trouble ordering from the website? I get to checkout and the bottom part has an error.

[Htown09]

Originally Posted by Former_Boosted_IS

USC, can you please see if HKS can make the 50003-M40XL and 50003-M45XL in a 14mm size?

Why? HL's already have the 14mm .

edit: the guy that is running them successfully in his N54 is running the XL plugs but he had to grind the hex housing from 16mm to 14mm in order to get them to fit.

HOWEVER, the HL plugs are already 14mm. So the only question is if the ceramic coating is too thin. We need a pic of stock plug and HL plug next to each other...