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2009 451 Rally Red, Pennzoil Platinum Euro 5W-40, Wix XP 51356, 185/55R15 tires, 44 psl
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Discussion Starter · #1 ·
Nearing 30,000 miles, time for new spark plugs.

OEM plugs are Denso
XU22HDR9 = Mitsubishi P/N : 1822A009,
Iridium = SXU22HDR8 = Mitsubishi P/N : 1822A010
(NGK ILKR7B8)

I am planning to go one heat range colder, NGK ILKR8E6 (Mitsubishi P/N = 1822A021)

Anyone use this plug?

I will have to re-gap it, it comes set at .024, (.6mm), I will go to .032, (.8mm)
 

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Make sure they match with the ones you takeout. I got a set that were quite a bit shorter in length of the threaded part.. I would stick to the stock heat range. I did go with the longer life plugs, then you don't have to change them as often.
 

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2009 451 Rally Red, Pennzoil Platinum Euro 5W-40, Wix XP 51356, 185/55R15 tires, 44 psl
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1,106 Posts
Discussion Starter · #4 ·
Actually fuel efficiency is determined by the gap, not the heat range...

OEM setting is .035, I am using .032..

Wider is more efficient, narrower is more horsepower....

Colder plugs just have less insulation, and run cooler...
 

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Like most spark plug upgrades, unless you're running some serious hardware on that engine or you have some bad misfiring going on, it's not going to make much (if any) difference.

https://www.ngk.com/learning-center/article/207/i-have-slightly-modified-my-motor---do-i-need

It appears the best you can do to a stock or mostly stock smart are long life iridium plugs. I've had a trio of those for over 60,000 miles until my engine coated them in oil.

I've gone back to the factory spec plugs after my 451's engine became healthy again. The high performance plugs I had installed after the fire did great at keeping the engine from misfiring... Though that could have just been a placebo since the issue with my engine oil fouled spark plugs and the oil fouling stopped not long after dropping in some MMO. Either way, the engine purrs like a kitten now and it's wearing factory spec plugs. :shrug:
 
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...if you are changing the air fuel mixture go colder...
...if you are changing the compression ration go colder...
...if you are driving for prolonged times at or above highway speeds go colder...
...if you are using methanol go colder...
...if you are running a turbo go colder...
...if you are changing the timing go colder...
...if not...let it be...you can always index and side gap for better flame propagation...

Jetfuel...horse power is not easy to find...
 
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