hotter plug or colder plug

[silvia lover]

i have couple bolt on for my 95' 240, such as header, exchaust, and intake. should i use the hotter spark plug for it or the colder one. I checked the denso website, but it just confused me. any help will counts.
P.S. the denso site said the plug we use for our 240sx heat range is 20. can i use a hotter plug llike 16 or colder plug llike 21~24(which one is better, btw, 16 is the hottest plug denso had and 24 and up is colder plugs)

[240sx2Nur]

Just go with the stock heat range. Unless you go forced induction or have a heavily modded N/A setup, other heat ranges are pointless.

[Jeff240sx]

From Centuryperformance.com
   A spark plug's heat range has no relationship on the actual voltage transferred through the spark plug. Rather, the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber. The heat range measurement is determined by several factors:

The length of the ceramic center insulator nose
The insulator nose's ability to absorb and transfer combustion heat
The material composition of the insulator
The material composition of the center electrode
   The longer the insulator nose gives you a larger surface area exposed to combustion gasses and heat is dissipated slowly. This also means the firing end heats up more quickly. We are talking about exposed ceramic length, not extended tip length.

   The insulator nose length is the distance from the firing tip of the insulator to the point where the insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. No matter what the plugs are installed in, be it a lawnmower, a boat, your daily driver or your race car, the spark plug tip temperature must remain between 450°C to 850°C. If the tip temperature is lower than 450°C, the insulator area surrounding the center electrode will not be hot enough to deter fouling and carbon deposit build-ups, thus causing misfires. If the tip temperature exceeds 850°C, the spark plug will overheat which can cause the ceramic around the the center electrode to blister as well as the electrodes will begin to melt. This may lead to pre-ignition/detonation and expensive engine damage. (see the plug pictures that are part of this article)

   In identical spark plugs, the differences from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing temperature is increased by 10°C to 20°C.

   The firing end appearance also depends on the spark plug tip temperature. There are three basic diagnostic criteria for spark plugs: good, fouled, and overheated. The borderline between the fouling and optimum operating regions (450°C) is called the spark plug self-cleaning temperature. This is the temperature point where the accumulated carbon and combustion deposits are burned off automatically.

   Bearing in mind that the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water journals. This means that the plug has a higher internal temperature, and is said to be a "Hot" plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.

   Conversely, a "Cold" spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range can be necessary when an engine is modified for performance, subjected to heavy loads, or it is run at high RPMs for significant periods of time. The higher cylinder pressures developed by high compression, large camshafts, blowers and nitrous oxide, not to mention the RPM ranges we run our engines at while racing, make colder plugs mandatory to eliminate plug overheating and engine damage. The colder type plug removes heat more quickly, and will reduce the chance of pre-ignition/detonation and burn-out of the firing end. (Engine temperatures can affect the spark plug's operating temperature, but not the spark plug's heat range).

Basically, you don't need to mess with the temperature of the plugs unless you do some heavy modifying, or have an ignition system.  Gapping the plugs correctly will give you the best power possible from the plugs.
-Jeff

[DarkRaptor42]

Jeff, what spark plugs do you use ie type and heat level.

[silvia lover]

thanks jeff and 240sxNur for the advise, because i order the denso spark plugs from a guy who host a groupbuy on groupbuycenter for a good deal <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'> (I only pay for $40 for 4 when i order it from him, i think that's cheaper than we use to pay for the same plug tho.) and he sent me the hotter plugs instead of the stock heat range. And i have found the exact same thing that you said on denso website. But it doesn't say anything about change it to the either hotter or colder plug will have wat kind a effect or anything similar to it, or the temperature inside the hotter plugs(just confused me by looking at the picture and the text). It just drive me nuts to figure will it be ok to fit a hotter plugs with minor bolt on.

[FSPtwo4d]

Basically, you can run the hotter plugs and get maybee a quarter of a horsepower with a higher risk of detonation, or you can run stock or slightly lower heat range plugs and not get that quarter of a horsepower, but you will keep the probability of detonation down. &nbsp;That's about it

Late

[silvia lover]

thanks FSPtwo4d, it clear the whole thing for me &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/cool.gif" border="0" valign="absmiddle" alt=':cool:'> &nbsp;I think i go for the NGK iridium IX plugs than, anyone know which model i should get for the 95' 240sx se? Because they have a bunch of different model and i'm not sure about it.