Could someone explain what is meant by "hot" spark plugs ? How do they effect engine performance.

Thanks, Eric

 

I know when you jump from say a BR9ES to a BR8ES it will be a hotter burning plug. Some people try to use these as a means of correcting poor jetting, which is not the proper way to go about it. Its more or less a band-aid to the real problem. I would suggest just running what manufacturer recommends.

 

You have to read the ground strap on the plug to determine heat range. Lots of things will effect the heat range - compression, jetting, and type of fuel for example. There will be a change in color on the ground strap, if it's right at the bend, you are good to go. If the color change is toward the tip of the ground strap, the plug is too cold and will not properly burn off any fuel deposits. Changing from a DP9 to a DP8 is changing to a hotter plug, you want the plug to hold just the right amount of heat so it burns off the deposits but not so hot that it cooks the porcelain. If the color line is closer to the plug body, the plug is too hot and you need to change to a colder plug or risk cooking the porcelain and/or holding so much heat in the plug that it causes the incoming air/fuel charge to explode before the plug fires (detonation). With my Raptor running a bit rich, I can get away with a plug that's one step colder than stock. Jetted down to "almost lean", I need to run a plug that's 2 steps colder to keep the color line at the bend in the ground strap. You can't properly jet the engine until you have the right heat range reading.

 

I learn something new everyday....... [img]i/expressions/face-icon-small-wink.gif[/img] Thanks UBETRUN.

 

In adding.....each heat range generally equates too 100 degrees of temp change. With too cold of a plug, an engine may not generate enough heat too make maximum power...or vice versa. No spark plug will yield more power if the proper heat range is set correct and firing correct.

 

Ubetrun,

Thanks for the info - sounds like the heat range of the plug really only impacts things when the engine is running and warmed up - or so. Do ya think the heat range selection can effect how easily a motor initially starts - in a kick start 4-stoke for instance ?

I'm thinking probably not.

Thanks again, Eric

 

Youre right, a hotter plug wont make a cold motor start any better. The hot and cold plugs are relative temps, they dont apply to outside temperature, they apply to the combustion temperature.

 

The only thing a spark plug heat range effects is the amount of heat the spark plug retains. A motor that's running high combustion temp will deliver more heat to the spark plug and if the plug is not the right heat range, it will retain too much of that heat and cause cooked porcelain and/or detonation. If the plug doesn't retain enough heat, it won't burn off the combustion residue and the porcelain will be dark brown or black. That's why it's so important to read spark plugs by the base ring and/or down inside where the porcelain and plug body meet. Trying to read spark plugs by looking at the porcelain isn't correct although that's the way 95% of folks do it.

Fisher - The proper plug gap has some effect on cold starting, you may want to check the plug gap if you are having cold starting problems.

 

Thanks again - feels like I learned a lot today [img]i/expressions/face-icon-small-smile.gif[/img]

 

Generally the spark plug heat range is defined by the type of riding you're going to be doing. According to the Honda shop manual, a hotter plug is recommended for a combination of low speed and cold outside temperatures. Conversely, if you're going to be doing a lot of high speed riding in a hot environment, a colder plug might be in order. My Honda came used with a colder plug installed, and it was definitely darker than it should have been. I changed to the standard heat range, but haven't pulled the plug to check since.

Chilly