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Message started by Digger on 06/27/09 at 19:54:36

Title: Thoughts on Running a Hotter Plug
Post by Digger on 06/27/09 at 19:54:36

Well, the Savage is down for phase maintenance.

Going through my records, I noticed that I'm running a NGK DP7EA-9 spark plug, which is one step hotter than the standard NGK plug (DP8EA-9) used by my bike (see signature).

I remember putting the hotter plug in there because I thought the cooler plug had fouled. Turns out I was having a petcock problem (see http://suzukisavage.com/cgi-bin/YaBB.pl?num=1152108113/7#7).

My Question: Having solved the rich running problem (that was due to a bad petcock), do I now replace the hotter plug with a standard plug, or do I just leave it alone.

I live at 6500 feet of altitude. The bike is used strictly for local duty, with short (less than 10 mile) spurts of 65 mph indicated. It's running good, but I've seen holed pistons in the past, presumably from plugs that were running too hot.

FWIW, the FSM mentions that the DP7EA-9 plug is OK to run if you see that the standard plug (DP8EA-9) is blackened by carbon.

Thoughts?

Title: Re: Thoughts on Running a Hotter Plug
Post by Gort on 06/27/09 at 20:09:42

Here is a good discussion about this subject, and also explains why regular grade gas is not always the best idea for the Savage engine, under certain conditions like extended idling or stop and start traffic conditions in hot weather, due to cylinder temperatures exceeding normal parameters. Personally, I never use a higher heat range plug in my Savage, especially due to the higher cylinder combustion chamber temps due to extended idling the summer

http://www.enginebuildermag.com/Article/16073/uncovering_the_cause_of_a_burned_piston.aspx

Title: Re: Thoughts on Running a Hotter Plug
Post by Stimpy on 06/27/09 at 21:48:37

Basically:
(as is my understanding :D)

- Hot plug: For short trips & city
In theory the spark is stronger and therefore your combustion more efficient.

- Normal: For longer trips and constant high revs
"Normal" spark means engine can be used and abused w/no risk.

I have used both kinds and barely felt a difference
...however it did run kinda crappy w/iradium dont know why

** @ 6500ft just leave it be, less oxygen up there! This means
a less efficient combustion so take all the help you can get.

Title: Re: Thoughts on Running a Hotter Plug
Post by Gort on 06/27/09 at 22:26:11

I copied this from the 'net. Pay special attention to the part about computerized, emmision engines like the Savage. Stay with the heat range Suzuki recommends, unless you have a worn out, plug fouling engine.

"Heat range

The operating temperature of a spark plug is the actual physical temperature at the tip of the spark plug within the running engine. This is determined by a number of factors, but primarily the actual temperature within the combustion chamber. There is no direct relationship between the actual operating temperature of the spark plug and spark voltage. However, the level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximum temperature and pressure occurs when the engine is operating near peak torque output (torque and RPM directly determine the power output). The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber but not vice versa. If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator causing a loss of spark energy or the actual shorting-out of the spark current.

A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug. A spark plug is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug. The heat range of a spark plug is typically specified as a number, with some manufacturers using ascending numbers for hotter plugs and others doing the opposite, using ascending numbers for colder plugs.

The heat range of a spark plug (i.e. in scientific terms its thermal conductivity characteristics) is affected by the construction of the spark plug: the types of materials used, the length of insulator and the surface area of the plug exposed within the combustion chamber. For normal use, the selection of a spark plug heat range is a balance between keeping the tip hot enough at idle to prevent fouling and cold enough at maximum power to prevent pre-ignition leading to engine knocking. By examining "hotter" and "cooler" spark plugs of the same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have more substantial ceramic insulators filling the gap between the center electrode and the shell, effectively carrying off the heat, while the hotter plugs have less ceramic material, so that the tip is more isolated from the body of the plug and retains heat better.

Heat from the combustion chamber escapes through the exhaust gases, the side walls of the cylinder and the spark plug itself. The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature. A cold plug will not materially cool down an engine's running temperature. (Too hot of a plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature.) Rather, the main effect of a "hot" or "cold" plug is to affect the temperature of the tip of the spark plug.

It was common before the modern era of computerized fuel injection to specify at least a couple of different heat ranges for plugs for an automobile engine; a hotter plug for cars which were mostly driven mildly around the city, and a colder plug for sustained high speed highway use. This practice has, however, largely become obsolete now that cars' fuel/air mixtures and cylinder temperatures are maintained within a narrow range, for purposes of limiting emissions. Racing engines, however, still benefit from picking a proper plug heat range. Very old racing engines will sometimes have two sets of plugs, one just for starting and another to be installed once the engine is warmed up, for actually driving the car."

Title: Re: Thoughts on Running a Hotter Plug
Post by PTRider on 06/28/09 at 07:43:39

Quote:

If the tip of the spark plug is too hot it can cause pre-ignition leading to detonation/knocking and damage may occur.

This is the most important part of Gort's posting for me. It is this detonation that burns holes in pistons.

I'd stick with the original plug spec unless that plug shows problems...and it probably won't.