What are the best spark plugs for the XU9J4/Z overall?

I can never see the benefit of uprated plugs on a standard engine. Plus Race plugs are stupidly expensive. Im unsure what the best ones are but id just say use standard ones and spend your cash elsewhere

spark plugs simply can't give you more power, you can actually loose power or damage the engine
if you use the wrong grade of plugs!

i've got Splitfire ones in my Mi16 and they run fine for a veeeery long time now (only adjusted once)
but i think that's their main advantage over standard ones.

just go with the standard (and correct!) ones and replace them when required .

I know they're not going to make power. Like I've heard some cars don't run well with platinums. I had Bosch +4's and i didn't like them very much.

Same, try ngk's, seems to run better.

Cooper or platinum or are iridiums worth the extra money?

Beru.

Yeah Beru. I get them from euro car parts for the BX16 valve, really cheap and they last as long as the f-ing Tosch super 4 ever did.

OE brand (at least for T16) is Eyequem.

I work at ECP and we used to sell these Denso IK20 Iridium plugs, which I put in the BX. Not a performance upgrade as such, but it starts easier, pulls smoother and the economy is actually better on motorway runs. They last for a long time too, I'm told.

Sounds interesting. IK20 is also the plug for my VR6...

Pretty sure they were IK20. May have been IK22.....I will need to check now!

Maybe Denso Iridium Power (IK22) will be best choice.
$80 for 4 plugs in Korea.
Almost same with genuine parts.
runs smoothly and last about 60,000 ~ 70,000 km. (MFG. suggest)

http://www.globaldenso.com/PLUG/search/index.html

My best mate had to spend £5000 rebuilding the engine in his 200SX because a Denso Iriduim plug disintegrated at high revs! I also know of 2 other people who have had them break apart, luckily without damage.

I wouldn't touch them with a barge pole!

I swear by Bosch super 4's.....i have them on mine and only replaced them last year after having the old super 4's on there for 4 years