Topic: Vex Denso Sparkplugs and Gap

[Nick1234]

This question has been beat to death, but I'm getting work done Monday at Vex, and was wondering what exact plugs you guys use in WRX's. As with NGK's website, the plugs Denso recommend show as having a .044 gap, which in overwhelming agreement on the forums is wrong. Can you confirm the gap size and plug you guys find to work the best to put this cat to rest? (and mind at ease).

-Nick

[LilDrunkenSmurf]

0.029 - 0.031 for the STi. I can only assume the WRX is similar. And yes, NGK for some reason sells 0.044 gapped plugs for Subaru.

http://forums.nasioc.com/forums/showthread.php?t=518633

Gap: Gap has a lot to do with igniteability. The bigger the gap, the better combustion. HOWEVER, this comes at a cost. The bigger gap requires MORE voltage to spark, puting a much higher strain on your ignition system. With a turbo charged motor, the gap is usually smaller. This is due to the fact that higher cylinder pressures make it harder for the plug to fire, therby increasing voltage requirments (this is why 2.5L NA is 0.044" gap and the 2.5L turbo is 0.030" gap). Can your ignition system handle the increased load?? Good question.

[Nick1234]

0.029 - 0.031 for the STi. I can only assume the WRX is similar. And yes, NGK for some reason sells 0.044 gapped plugs for Subaru.

http://forums.nasioc.com/forums/showthread.php?t=518633

Not sure if and why it makes a difference, but the plugs I pulled out initially AND the plugs Chris at Touge stock are "L" prefix type, meaning more threads and longer plug, sits deeper into the combustion chamber. Would this add compression? My brain tells me yes, according to physics. I have short plugs in now, and they sit flush with the combustion chamber. I noticed a power drop since, and its depressing. The power drop could also be because it's a Bosch plug. I don't know. I guess the reason I'm trying to find out the exact plug is to not only find out the gap Vex uses, but also the plug length. I have a spark plug complex since the last time I changed plugs.


-Nick

[LilDrunkenSmurf]

Check the second post in that thread. The 2.5L uses the longer plug. The 2L does not (it looks like).

[Nick1234]

Check the second post in that thread. The 2.5L uses the longer plug. The 2L does not (it looks like).

Nice find. Makes total sense now!

[LilDrunkenSmurf]

I know that the 2.5L coilpacks are shorter than the 2L (or vice versa, I can't be bothered to remember this morning), so that might be relevant as well.

[RWDragoon]

Yes the 2.5 and 2.0 use different plugs.  It's not the coil packs but the actual length of the plug.

The Denso's run a 0.4mm electrode and gap depends on which plug you use, very consistent out of the box.  We have had great success with these plugs.  The Racing plugs we stock are amazing quality as well.

[Nick1234]

Yes the 2.5 and 2.0 use different plugs.  It's not the coil packs but the actual length of the plug.

The Denso's run a 0.4mm Gap, very consistent out of the box.  We have had great success with these plugs.  The Racing plugs we stock are amazing quality as well.

I'm confused. So, the Denso plugs work with a .044 gap in turbo 2.5's, but the NGK's work best with a .032 gap in turbo 2.5's?

[LilDrunkenSmurf]

0.029"-0.031", not mm. Not sure why the denso would be so tiny @ 0.4mm (0.015")

[Nick1234]

0.029"-0.031", not mm. Not sure why the denso would be so tiny @ 0.4mm (0.015")

Ahh ok, so .015 Densos. Hmmm.

[Nick1234]

Did some research:


NGK vs. Denso

FACTS:
- Denso (1949) is a newer company than NGK (1936)
- “24” on Denso’s heat range scale is the equivalent of “8” on NGK’s scale
- Construction of NGK and Denso plugs is similar
- Denso plugs have a smaller center electrode (0.4 mm – claimed to be the smallest in the world) than NGK plugs (0.6 mm)
- The narrower the center electrode, the lower the potential difference (voltage) that is required to jump the gap between center and ground electrodes
- Denso plugs require a lower ‘spark jump’ voltage than NGK plugs
- The smaller diameter of the Denso center electrode means that less wear can take place before the plug’s optimum service life is exceeded

All from this nice thread:

http://www.wrxtuners.com/forums/f103/man-show-s-spark-plug-info-27782/

[RWDragoon]

This is what Denso recommends and what we use and stock. 

EJ20 Turbo Engines:
IK20 1.1mm gap
IK22 0.8mm gap (one range colder)
IK24 0.8mm gap (two ranges colder)

EJ25 Turbo Engines
IKH20 1.1mm Gap
IKH22 0.8mm Gap (one range colder)
IK01-24 0.8mm Racing Spark Plug 2 ranges colder

Disregard my first post the electrode is 0.4mm tip, not the gap! 

[Zaider]

1.1mm = 0.043" --> bigger than what Subaru recommends.
0.8mm = 0.031" --> just right.


Nick, based on your mods in your project thread, I wouldn't worry about 2 steps colder plugs as that's too far. If I were you, i'd probably end up with the IKH22 or the NGK equivalent (I think the iridiums are LFR7AIX)

[Nick1234]

1.1mm = 0.043" --> bigger than what Subaru recommends.
0.8mm = 0.031" --> just right.


Nick, based on your mods in your project thread, I wouldn't worry about 2 steps colder plugs as that's too far. If I were you, i'd probably end up with the IKH22 or the NGK equivalent (I think the iridiums are LFR7AIX)

Ok, now it all makes sense. Thanks all!