Spark plug DPR8Z----DPR9Z???

[ewalker302]

In my manual it calls for the (NKG)DPR8Z, then says for extended high speed riding use DPR9Z.

My question: Is the 9Z better for trail riding in a modded 400 (pipe, filter, dedree key), or is the 9Z just for racing??

Also plug gap, the manual calls for .024" - .028" gap.

Has anybody played around with the gap on a bike modded like above?

I know bigger gap/bigger spark, just wondering if those mods would be enough to justify using the 9Z or increasing the gap??

Or if it will harm the 400 to trail ride with the 9Z??

Just wondering, never seen this brought up before.

:bandit:

[ridesa02400EX]

i dont think it really matters. ive used both and saw no noticeable difference.

[Guy400]

The "8" and the "9" are heat ranges, with 8 being the hotter of the two. The 8 offers the hottest burn but raises combustion chamber temps by 70-120 degrees F (claimed by Autolite). The 9 will reduce temps, be a little more resistant to detonation/preignition but you run the risk of fouling plugs a little more often. You won't see any power increases/decreases.

[ewalker302]

OK??

The combustion chamber temp? Wouldnt that affect the engine operating temp not just the combustion chamber.

DPR8Z is stock.

70-120 degrees cooler with the 9?!

How can that not affect performance?

I knew the 8-9 was colder/hotter plug.

But im confused.

Seems like cooling the 400 is on the top of everybodys list.

People are buying air scoops, bigger oil tanks, bigger/alternative oil coolers every day, expensive stuff too & you get 70-120 degrees cooler by switching from the stock plug to a DPR9Z!?

I never fouled the plug with the stock one.
But I may if I run a cooler plug? That part I can see sorta.
I never really fouled a plug on a 4 stroke.
Flooded em, sure.

Not trying to dispute, just dosen't make any sense.

:bandit:

[Guy400]

Originally posted by ewalker302
OK??

The combustion chamber temp? Wouldnt that affect the engine operating temp not just the combustion chamber.

DPR8Z is stock.

70-120 degrees cooler with the 9?!

How can that not affect performance?

I knew the 8-9 was colder/hotter plug.

But im confused.

Seems like cooling the 400 is on the top of everybodys list.

People are buying air scoops, bigger oil tanks, bigger/alternative oil coolers every day, expensive stuff too & you get 70-120 degrees cooler by switching from the stock plug to a DPR9Z!?

I never fouled the plug with the stock one.
But I may if I run a cooler plug? That part I can see sorta.
I never really fouled a plug on a 4 stroke.
Flooded em, sure.

Not trying to dispute, just dosen't make any sense.

:bandit: Yes, combustion chamber temperatures would increase overall operating temperatures. I just assumed the two would be equated.

As I stated, Autolite reported the 70-120 degree heat difference between the two heat ranges but that was in a single cylinder of a passenger car engine of unspecified size. I don't know how it would specifically affect the 400EX.

When I owned my Cannondale the common thing to do was switch to hotter plugs to reduce plug fouling. No increase in performance was gained and no noticeable affect was made to how often or how long the cooling fan came on.

[stupid driver]

Ive run both of them, and the only thing different about them was there was a little less engine heat w/ the dpr9z. 4 degrees. This is on an 11.1 425 piston.

[cals400ex]

i think dusty noticed almost a 50 degree drop in oil temp when she switched from the stock plug to the colder one. however, she also added air scoops at the same time. je and ross says that the dpr9z is highly recommended when running one of their higher compression pistons. i run the colder one in all but the winter month.

[quadmxracer]

SHIFT
K&K

[Holeshot36]

Uh there fuel injected yes and they also have spark plugs. Every combustion engine has spark plugs fuel injected or not.

[ewalker302]

Originally posted by Holeshot36
Uh there fuel injected yes and they also have spark plugs. Every combustion engine has spark plugs fuel injected or not.

What the hell are you babbling about??

[cals400ex]

Originally posted by ewalker302
What the hell are you babbling about??


lmao he kind of through me off too with that reply.

[Guy400]

I'm as lost as the next guy:confused:

[400ex#18]

all i can say is that i ran both, and in the cooler weather run a hotter plug, and in the hotter weather, run a cooler plug..also, if you are buying these plugs from ngk, it could make a difference from running like a slitfire plug or honda. i don't know what difference, but i just run ngk dpr8z in the winter, the the 9z in the summer.

[Holeshot36]

Originally posted by ewalker302
What the hell are you babbling about??
Hey man thats messed up quadmxracer changed his post where is say k&k and shift, he said "arn't dales fuel injected so they don't have spart plugs" he must have realised what he said and changed it lol.:huh

[cals400ex]

Originally posted by Holeshot36
Hey man thats messed up quadmxracer changed his post where is say k&k and shift, he said "arn't dales fuel injected so they don't have spart plugs" he must have realised what he said and changed it lol.:huh


that makes a little more sense now