Spark plugs?

[corksil]

Hey guys -- I ordered some spark plugs from bike bandit and they showed up yesterday. Today is maintenance day and upon inspecting the plugs, they are [NGK] CR7E. I pulled the plugs out of my bike to inspect/replace, and the ones in the bike were CR8E's.. one colder heat range.

I called the local bike shop, then another -- and verified that the OEM spec for the plugs were 8's.. One person even went as far to explain that he had a sportbike and he had overheating problems with 8's as well. He recommended that I run heat-range 9 plugs for extra protection.

I went ahead and bought some CR8E's, as recommended by (apparently) the manufacturer.

Does anyone have experience with this? Am I going to be good with the 8's or should I try running something colder? I would consider myself a _hard_ rider as the bike is only a 250.

Without an AFR or EGT gauge, there's really no way of telling what's going on inside the combustion chamber and I'm not going to get that deep with this bike. I suppose I could borrow an infrared thermometer and monitor the temp of the primary manifold runners, but that still wouldn't tell me anything about the AFR or how the mixture was burning.

Where I live, ambient temperatures are 70-80*F all year long.

[Motofool]

Originally Posted by corksil

...........Without an AFR or EGT gauge, there's really no way of telling what's going on inside the combustion chamber and I'm not going to get that deep with this bike.........

Don't sweat it, the recommended plugs are NGK CR8HSA:
http://faq.ninja250.org/wiki/Changin...rands_to_avoid

[corksil]

Does anyone run a heat range up or down from the 8's?

I've got a set of sevens and nines I can try out, but I'm not sure how I could quantify the change -- if any. Shooting in the dark unless someone has information on this.

[cuong-nutz]

Originally Posted by corksil

Does anyone run a heat range up or down from the 8's?

I've got a set of sevens and nines I can try out, but I'm not sure how I could quantify the change -- if any. Shooting in the dark unless someone has information on this.

Only if your are running a heavy modded engine that requires it. Otherwise, stick to stock.

Ngk all the way!
http://www.ngksparkplugs.com/tech_su...k_plugs/p2.asp

[Motofool]

Originally Posted by corksil

've got a set of sevens and nines I can try out, but I'm not sure how I could quantify the change -- if any. Shooting in the dark unless someone has information on this.

Being an aggressive street rider, you could try the 9's.
If too much carbon builds up, then you will know that 8's will be better.

I don't know how much difference the 7's would do, but I would not use them, since the temperature in the combustion chamber would increase, maybe to the point of inducing destructive pre-ignition.
It is not uncommon to see melted pistons in these bikes, mainly from using Champion plugs of equivalent heat rate.

The reason for these engines to use liquid cooling is to keep a narrow range of chamber temperatures and tighter tolerance between the metal parts.
Introducing changes in the heat rate of plugs would move the engine's parts out of their comfort zone.

[quarterliter]

I'm debating running a set of 7s in my ninja. Do the any of the racers out there run 7s because of the consistent high RPMS?

[DaBlue1]

Originally Posted by corksil

Does anyone run a heat range up or down from the 8's?

I've got a set of sevens and nines I can try out, but I'm not sure how I could quantify the change -- if any. Shooting in the dark unless someone has information on this.

Given the ambient temps you ride in, you will be fine with the CR8E's, unless you're running a heavily modified engine like Racer X (who runs 9's)

[quarterliter]

Can someone explain why a heavily modded engine would need a hotter spark plug?

[DaBlue1]

Originally Posted by quarterliter

Can someone explain why a heavily modded engine would need a hotter spark plug?

The lower the number the hotter the plug. The higher the number the colder the plug. The differences is the length of the insulator nose. The insulator nose of a hotter spark plug has a longer distance between the firing tip of the insulator, and the point where insulator meets the metal shell. Therefore, the path for the dissipation of heat from the insulator nose to the cylinder head is longer and the firing end stays hotter. The insulator nose of a hotter spark plug also has a greater surface area that is exposed to more of the ignited gases and is easily heated to higher temperatures. ( this is why some use 7's in the extreme cold of winter-easier cold starts) A colder spark plug functions in an opposite manner. A heavily modified engine (nitrous, etc..) can tend to generate slightly higher combustion chamber temps.

[quarterliter]

Is there any significant power advantage to running a hotter plug?

[DaBlue1]

Originally Posted by quarterliter

Is there any significant power advantage to running a hotter plug?

Nope.

[corksil]

Originally Posted by Motofool

Being an aggressive street rider, you could try the 9's.
If too much carbon builds up, then you will know that 8's will be better.

I don't know how much difference the 7's would do, but I would not use them, since the temperature in the combustion chamber would increase, maybe to the point of inducing destructive pre-ignition.
It is not uncommon to see melted pistons in these bikes, mainly from using Champion plugs of equivalent heat rate.

The reason for these engines to use liquid cooling is to keep a narrow range of chamber temperatures and tighter tolerance between the metal parts.
Introducing changes in the heat rate of plugs would move the engine's parts out of their comfort zone.

I agree. Without an EGT or AFR gauge on the tailpipe, there wouldn't be any quantifiable changes to examine. With such a small motor, any change in "feel" would be largely psychosomatic.

The 8's didn't look bad, no evidence of detonation from a lean burn, and no evidence of major soot in the exhaust indicating a rich mixture, so I suppose there's no sense in messing with plugs.

I don't think that changing the heat range of the plugs by one number would move anything too far out of 'spec' in terms of what the engine was looking for, but after thinking at length about this -- I just don't think there's any power/performance to be gained, especially not on a stock engine.

[corksil]

Originally Posted by DaBlue1

The lower the number the hotter the plug. The higher the number the colder the plug. The differences is the length of the insulator nose. The insulator nose of a hotter spark plug has a longer distance between the firing tip of the insulator, and the point where insulator meets the metal shell. Therefore, the path for the dissipation of heat from the insulator nose to the cylinder head is longer and the firing end stays hotter. The insulator nose of a hotter spark plug also has a greater surface area that is exposed to more of the ignited gases and is easily heated to higher temperatures. ( this is why some use 7's in the extreme cold of winter-easier cold starts) A colder spark plug functions in an opposite manner. A heavily modified engine (nitrous, etc..) can tend to generate slightly higher combustion chamber temps.

Again, I agree with everything you said.

However I'd like to amend -- "heavily modified engines can generate slightly *higher* combustion chamber temps."

I'd like to add that it's not so much the higher temperatures as it is higher pressures. A higher combustion chamber pressure would require more thermal energy (spark) to ignite the mixture -- that's why people often open up the plug gap when they switch to hotter plugs.

And finally -- as per my understanding with the race motors I have built in the past -- a hotter plug also serves to help keep combustion chamber temps under control. The length of the electrode helps to wick excess heat out of the combustion chamber and into the cylinder head and subsequently the cooling system as well.

There is a very narrow temp range of where each type of fuel burns most efficiently -- too hot, and the mixture "flashes" too quickly -- and not hot enough, often results in an uneven burn and poor power production.

But now we are getting into engine theory and rod/stroke ratios and different types of fuel etc. None of which are relevant to this discussion.