"Spark Plug heat range"

[BSNMOE]

Many of "Pelicans" have stated that when they used hotter plugs, their cars actually ran cooler. The NGK site states that if you want your car to run cooler use a colder plug. I'm wondering if air cooled cars are unique that they dissapate heat more efficiently through the exhaust rather than the air flow around cylinders? If this is the case should we all run a hotter plug?

[moneymanager]

With all due respect to fellow Pelicans, I'd take NGK's advice over them any day on a question of this kind.
But it isn't primarily a cooler running car that you'd expect from colder plugs. Rather it's lower combustion chamber temperatures which are the goal. And here the science isn't subject to much debate: a cooler plug will dissipate heat from the combustion chamber faster... that's what it is designed to do.

[snbush67]

NGK and Bosch have different numbers in regards to heat, and heat dissapation.

[lvporschepilot]

The idea is to use the *coldest* plug that will not foul. You can tell if your plug has the correct heat range if the ground strap has color to the apex and no further. Using too hot a plug will cause light detonation at upper rpm and will affect power. Plug reading now is completely different than it was 30 years ago when fuel was different. Fuel is very quick burning now and does not leave the same residue as it used to. Even NGK's chart is 30 years old so please do not pay any attention to it.

The below listed plug shows correct heat range and timing, but this plug is actually running very rich all over the rpm range.

[T77911S]

i have done a lot of seraching on the net about reading plugs. the one thing i have come to understand is that there are several thoughts on reading plugs. some say the ground strap shows timing, some say the porcelein is for heat range or the base of the plug is for heat range.

i see NGK has changed their site. here is what i copied off their site a while ago. this is their words,not mine. i will paste all i copied, you may find it helpfull.


this is from NGK's site.

Pre-ignition: is defined as the ignition of the air/fuel mixture before desired ignition timing

Detonation: is a spark plugs worst enemy. It can break insulators and ground
electrodes. Spark plug temperatures can reach in excess of 3000 °F.
Detonation, in simple terms, is a violent uncontrolled burn of the air/fuel

mixture, which occurs when excessive heat and cylinder pressure causes the air/fuel mixture to spontaneously ignite.

By examining the insulator firing nose color, an experienced engine tuner can determine a great deal about the engine's overall operating condition.
In general, a light tan/gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Dark coloring, such as heavy black wet or dry deposits can indicate an overly-rich condition, too cold a heat range spark plug, a possible vacuum leak, low compression, overly retarded timing or too large a plug gap. If the deposits are wet, it can be an indication of a breached head gasket, poor oil control from ring or valvetrain problems or an extremely rich condition - depending on the nature of the liquid present at the firing tip.




The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal
Performance", and is determined by the heat range selected. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at a high rpm for a significant period of time.

However, when compression is raised, along with the added power comes added heat.

Since spark plugs must remove heat and a modified engine makes more heat, the spark plug must remove more heat. A colder heat range spark plug must be selected and plug gaps should be adjusted smaller to ensure proper ignitability in this denser air/fuel mixture.

Typically, for every 75-100 hp you add, you should go one step colder on the spark plug's heat range. A hotter heat range is not usually recommended except when severe oil or fuel fouling is occurring.

It is a common misconception that spark plugs create heat. They don't. A heat range refers to how much heat a spark plug is capable of removing from the combustion chamber.

Selecting a spark plug with the proper heat range will insure that the tip will
maintain a temperature high enough to prevent fouling yet be cool enough to prevent pre-ignition. selecting a spark plug in the proper heat range will ensure that the spark plug itself is not a hot spot source.

ignition timing directly affects the firing end temperature of the spark plug.
Advancing the ignition timing prolongs the time to compress the burning gases. The pre-ignition temperature also elevates gradually, since the pressure and
temperature of the combustible mixture is low before ignition. Advancing your
timing elevates firing end temperatures.

the by-product of increased compression is the elevation in cylinder temperatures.

NGK Spark Plugs recommends dropping heat ranges and altering Air/Fuel mixtures and timing as needed. It is very important to dissipate the excess heat from the
combustion chamber in order to prevent pre-ignition.



Air/Fuel Mixtures seriously affect engine performance and spark plug operating
temperatures.

Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor
driveability
Lean air/fuel mixtures cause plug tip and cylinder temperature to increase,
resulting in pre-ignition, detonation, and possibly serious spark plug and engine
damage

Higher Compression Ratios/Forced Induction will elevate spark plug tip and
in-cylinder temperatures. As compression increases, a colder heat range plug,
higher fuel octane, and careful attention to ignition timing and air/fuel ratios
are necessary. Failure to select a colder spark plug can lead to spark plug/engine
damage


Setting the gap for your particular engine is important as insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Whereas too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy.
For modified motors, proper gapping is essential; gap settings are affected by increased compression, fuel type, turbos, nitrous and high output ignition system. Most experienced tuners know that opening the gap up to present a larger spark to the air/fuel mixture maximizes burn efficiency.


here is some info i got from another site, i dont remember where. a lot of this stuff comes from drag racer sites. but this contadicts the above statement about the ground strap, again, not my words, just what i found on the net.

a spark plug should be getting hot enough to keep its insulator nose completely clean, with all deposits burned away, but not so hot that its electrodes show signs of serious overheating. These are things to look for on a new plug that has been subjected to a few minutes of hard running

Ignition timing is directly responsible for the heat in the combustion chamber and therefore the color of the plug’s ground strap and the color of the first few threads on the outside of the plug.




if you want more, i have more i can post. i should really go back and clean up all the stuff i have copied.

i did do some testing with heat ranges. i put in a set of used W4 (from a 930 turbo) plugs, pretty cold plug BTW. i did not foul to the point of not starting, but the plugs were black, except when i took a 800 mile trip. as soon as i got there, i pulled a couplpe of plugs and they were grey, or clean, like when i put them in, which is what i expected. really the only need for a hotter plug is for startng, idling and low rpm driving where the mixture is richer. i then put in W5's (bosch, one step hotter), and even though it still ran fine, i enden up with the NGK BPR6, which is the same as the W5, again, one step hotter. and as for your concern of engine temps, i did see a slight increase on temp. but then, if my oil temp is up, is my combustion temp down, which is were the real damage can occur if it is too high.....in the form of detonation or even worse, pre ignition.

[BSNMOE]

I also did some testing on my 2.4S MFI, MSD and plugs gapped at .045.. I had AFR at 13.1 using NGK #8's.. The car ran fine, plugs pretty clean and tail pipe clean. I then went one click rich on the main and 2 rich on the idle and the car idled smoother, ran much better, however, the plugs were a little sooty and so was the tail pipe. I then went to #7's (hotter) which cleaned things up a little but I worry about 7,000 RPM's on a hot day! If I leave the MFI one click richer and go back to #8's, the plugs and pipe really get sooty. The plugs don't foul just look black, except the firing tip is clean.

[T77911S]

i would not have thought the plugs would have anything to do with soot in the pipe. but perhaps it is due to the combustion chamber temps (???)

if you can run the hotter plug without detanation, use it, if you are going to track the car, change the plugs to a colder plug if you are worried.

13.1 is rich. you made it more rich from this point? take a look at your timing(?)

here is another test you could do . run the car steady for a while to clean the plugs, IE, dont let it idle, shut it off and pull a plug. try it with the 8's.

do you have access to an LM?

[snbush67]

sparkplugreading

[lvporschepilot]

Optimal thermal operating range is 700C-800C. A racing engine may see temps in the 2500-3000F range. Different heat range plugs afford slight variances in ignition timing. Dyno tuning is obviously optimal, but starting at OEM specifications and moving up little by little until trace detonation is found works as well. This takes time and one who is very good at discerning when an engine has some detonation which can be very difficult to tell at high rpm. Often time people say their engine has a 'flat spot' at higher rpm which many times is nothing more than detonation which they were never able to discern. The plugs will have little shiney spots on the ceramic or ground strap. That is aluminum from the detonation.

The best rule of thumb when checking the best heat range for your engine is to bring the engine to operating temperature with new plugs and then making a WOT run in a reasonably tall gear and then shut the engine off as immediately as possible (preferrably right after the run). Pull the plug and read the ground strap and to what point before the apex (too cold) or after the apex ( too hot) there is color or a line. By racing standards, a 'perfect' mixture on street fuel is determined by reading the same plug after the above test and inspecting the soot ring around the base of the ceramic insulator. The ring should be about 2mm thick (varies by engine). Do not be alarmed by a clean white insulator as this is perfectly natural with modern quick burning fuel.

[RoninLB]

my routine is to find optimal EGT for my routine then pick the coldest NGK that doesn't foul

if oil or CHT temps are to hot fix it

it may be safer to run rich A/F readings than hot but all's a waste of safe performance

[BSNMOE]

When I do my testing I get the car hot, install new plugs, drive off for 1/2 hour run at 3 to 6,000RPM. As I stated along with MSD my 2.4S has complete engine rebuild, new pump, new distributor. Even at 13.1 AFR my plugs read "rich" whether I use #7 or #8's.. I wonder when I had the AFR set up that the probe(sniffer) was not attached far enough up the exhaust pipe so some fresh air was mixed with the exhaust and I got a 13.1 reading. It may be richer than that. I no longer have access to a LM-1 to recheck but the car sure runs better one click rich from the 13.1 reading, but, the plugs are a little sooty. The hotter plugs clean things up a bit.

[RoninLB]

one of our local popes say best gap is .040" w/MSD

[T77911S]

NGK says to go by the insulator color, not the ground strap. other sites i have found say the ground strap "aneeling point" is the sign of timing. the test i did followed this. the cold plug had a black insulator, grey when i did a long trip, the next higher was not as black, more grey but not as clean as i wanted, the W6 had a clean insulator. so a either W5 or 6 would be good in my car.

13.1, is that idle or steady driving? that is very rich for 3k RPM. i average around 15 or so at that RPM. 13.1 is around what you might see at WOT.

8 is probably too cold, that is = to W4, which is what a 930 would run. W4/8 (bosch/NGK) was very black in my car. the W5/7 was ok. i may go back and try the W5/7 again.

[tobluforu]

You should see the plugs on my mfi car, very sooty and it has been like this since I rebuilt the fraken motor 15 years ago, but the car runs like a top and they do not foul (I have since gone to a hotter plug). You should see the plugs on my 2002 viggen that is pretty well built with over 300whp, plugs are off white as trionic has a plug cleaning cycle it goes through whenever you shut the engine off. The plugs on the old sc viper were the same way, but that 600whp beast had a great a\f ratio as well. Plugs are just one way to get your car to perform and they are not the tell tale sign. Back in the day, it was pretty much all we had to go by as there were no lm1's for 60-70's muscle cars and no one had money to go to dyno's so we read plugs, adjusted the carbs, set timing and off we went.
MFI cars like to run rich.

[T77911S]

Originally Posted by snbush67

sparkplugreading

i have seen this site. i find more that go against it than with it.

lots of info here.
How you can read spark plugs and select them - by Gordon Jennings.

Century Performance Center, Inc. :: Spark Plug Tech

Spark Plug Reading 101 by Mike Canter

Spark plug reading

Spark Plug Tuning Pro Stock Style- Car Craft Magazine

lots of pics
Spark Plugs

this one goes against the grain
How to read Racing Spark Plugs

my conclusion on this? since timing does effect heat, select the heat range based on the insulator, fine tune the ground strap with timing. but start with a cold plug and work your way hotter.

do i really look at any of this? no, i connect the LM and check the mixture, the plugs look, at a glance, clean, and it runs fine. i just thought reading plugs was interesting. besides, you have to do all this with fresh plugs and after a "drag" run.

[BSNMOE]

Reading my plugs idicates that I have a very rich idle and somewhat rich part load or main rack.. Idle AFR is 12.6 the main after 3,000RPM is 13.1. My timing is set at 3 deg. ATDC which is a little advanced but, this makes a better off idle transition. If I go leaner on the idle I get a little off idle hesitation. Also, if I go one click lean on the main , I feel the car does not perform as well. However, the plugs look much better. Now 12.6 to 13.1 AFR does not seem that rich, especially with the gas of today, and I said before , If I go one click more rich, use a hotter plug, the car performs much better.

[911pcars]

Spark plug heat range creates the operating temperature of the insulator to burn off deposits that would ordinarily cling to it. If it doesn't conduct heat fast enough (heat range too high), it may cause pre-ignition. If the plug conducts heat away from the insulator too rapidly (i.e. "colder plug"), deposits will build and perhaps short out the gap and prevent a spark (combustion).

Combustion temperature/pressure is a function of A/F mixture, altitude, engine load, timing and other factors, not the spark plug.

Sherwood

[RoninLB]

Originally Posted by BSNMOE

, and I said before , If I go one click more rich, use a hotter plug, the car performs much better.

I agree

tune the car 1st and adjust the plug range 2nd