Lore has it that w see these goofy screw-on end caps for plugs because some ancient cars actually had metal "o" rings on the end of the plug wires that screwed on.

The caps were added to accommodate the vast majority of "normal" cars that use snap-in end connectors....

Crazy, huh ?...especially since these guys love to get loose and come off...and at the wrong time too !

- Wil

Voltage / Spark Intensity
The lower the voltage requirement of a plug, the less intense the spark will be.

On high compression engines, you need a more intense spark than on a lower compression engine.

The air gap between the center elecrode and the ground electrode is the highest point of resistance. If you reduce the gap, you reduce the voltage necesarry for a spark to jump the gap. If you increase the gap, you increase the voltage requirement.

Heat Range
Selecting the proper heat range for your plug is also very important, as a plug performs best in the range it was designed for. It is also one of the harder balancing acts.

Many people think the plug is only there to ignite the F/A mix, and do not understand that the plug is designed to also help remove heat from the combustion chamber. The "heat range" noted on plugs is not the operating environment they are designed for (IE: do not use HOT plugs in a HOT engine) but are instead a statement of their ability to remove heat from the engine.

So if you have a hot-rodded engine that is developing hotter head temps than stock, you will need to go to a slightly colder plug. Similarly, if your engine will be run at high RPM for long periods of time, you will need a slightly colder plug.

Also, a spark plug's heat range has no relationship to the actual voltage transferred though the spark plug. However, overheated plugs can crack and drop debris in the cylinder... not good. Also an overheated plug is a "hot-spot" in the cylinder that can lead to damaging pre-detonation.

If you do not have oil seepage into the cylinder, fouling is often an indicator that your plug is not acheiving it's optimum operating temperature. This can be corrected by moving to a hotter plug.

So, increasing the gap from say, 0.28" to 0.30" may increase spark intensity? Based on the logic of increased resisitance equals more intense spark, the resisitor type plugs are the way to go?

The resistance that increases the spark strength is the gap only. A resistor plug will not do anything to increase spark strength. What the iridium folks say is that since the plug requires less voltage to fire, they can run a bigger gap. A balancing act of sorts that gives a very strong spark. Both NGK and Denso advertise their iridium plugs as their "high end high performance" plug. Plus they last longer and retain their performance characteristics longer - much longer than other plugs because the iridium metal is very hard.

I thought that the heat range for a plug was it's ability to dissipate it's own heat, not to remove heat from the engine.

But, much of the popular opinion on this site says a standard low tech plug is best for performance vs. what the new iridium plug's advertise. Maybe installing the iridiums with a slight increase in gap is the way to go?

I see lots of talk about dual-plug heads too. I guess to each their own. If you go to their site, it will say be very careful about gapping iridium plugs because you can break the electrode very easy. I have not checked but they might come with a slightly larger gap from the factory.

However, it may be a matter of perspective. Spark plugs alone do not heat up (for example, when being tested in a bench box). Only when there is combustion is there heat to be dissipated or transferred from the cylinder. So is the plug transferring "it's own" heat away, or the heat of the combustion process... ?


Dual plug heads really serve an unrelated purpose.... they are so that the combustion mixture is ignited from two points for a more even and more complete burn. It also results in a faster burn, meaning that less timing advance is necessary. These features can be especially helpful when using big cams and/or forced induction.

I agree that it might be a matter of perspective. Granted anything that sticks out of the side of an engine dissipates heat (sensors, plugs, brackets, etc.), I just find it really hard to believe that engineers would design spark plugs as a means of cooling off an engine. If so, we'd have these huge, vaned contraptions controlling our sparks.

From the Bosch site:
The so called “heat range”, which is assigned to each spark plug, is used to characterize these heat dissipation capacities. A plug with a low heat range number (e.g., 2-4) indicates a cold plug that quickly dissipates heat to the engine block and cooling system, while a high code (e.g., 7-10) indicates a hot plug that retains heat. By properly selecting the heat range of the plug, it ensures that the plug will operate between the plug’s designed operating range of 500-900 degrees Celsius. In this range, the spark plug will be self-cleaning, yet will not be hot enough to pre-ignite the air/fuel mixture.

All in all, I agree with the NGK and Denso quotes but I think all the unwanted thermal energy is directed at the plug and more importantly, the plug tip and not the engine itself.

Here's some info from Champion that proves your point:

The spark plug can help maintain the optimum combustion chamber temperature. The primary method used to do this is by altering the internal length of the core nose, in addition, the alloy compositions in the electrodes can be changed.

My turn:

From Wikipedia:
http://en.wikipedia.org/wiki/Spark_plugs

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

In late but go NGK copper. Very high quality boom for the buck plus phenomenal heat range!

87 blk coupe ;)

[QUOTE]Originally posted by cashflyer
[B]Voltage / Spark Intensity
The lower the voltage requirement of a plug, the less intense the spark will be.

On high compression engines, you need a more intense spark than on a lower compression engine.

Total agreement, see my posts on the problems with my supercharged engine and high rpm misfiring. When I changed to Denso iridium I got clean 7000 RPM pulls with no misfiring and 7500 miles later still perfect. Not dogma just real world fact. Also Amsoil is great.

Best regards,

I just removed the Bosch platinum W5DPO plugs from my 1977 2.7L. I have never seen more carbon on any plug - ever. With 6,000 miles on them they looked like they had been in since 1977.:eek:

I put some NKG BP7ES plugs in, changed the rotor and distributor cap. I still need to do the timing but a huge improvement already.

At $2.16 a plug I'm going to change the plugs every year.:)

I agree.

I have a 71' 911E with MFI. I pulled my "fancy" and expensive plugs yesterday and after 16 months, they're black. Since MFI cars run rich even when dialed in properly, I'm just going to clean these fancy plugs now and replace them in a few weeks with the NKG's and probably replace them every year or two.

Gavin

I just replaced my 930's plugs with stock ones, being that they are a very cold plug and Im in Arizona heat, I think its best. Anyone know of a better 930 plug than stock?

Is it possible to run one step cooler on a USA 3.2 during D/E's or hot days? I'm running BPR7EIX (NGK), which is one step cooler than the 6.
j.p.

In another plug thread, John Walker seems to sing the praises for the Denso irridiums for the carbuerated engines, keeping fouling to a minimum. I recently invested in the Denso irridiums on an SC and seemed very pleased. My gas mileage has improved.

There are so many variables from engine to engine. From my experience, my engine (78') has the lower compression so the seemingly less intense spark of the irridiums work well. I experimented with Bosch platinums and NGKs. It seemed to run more efficiently with a slightly less gap than recommended but tolerated less timing changes.

I feel very happy with the Densos.

I pulled Denso's from my Geo Tracker, they looked pretty good except for one thing. Somehow the gap was double what it should of been. I don't remember if I did the plugs for sure or if I had a shop do it, been four years at 2,500 miles a year and time for a change anyway. They were pretty lose, could almost pull them by hand but not quite.

NGK or Bosch copper cores - the cheap ones. I have had nothing but problems with Beru Silverstones, Bosch Platinums, etc- any precious metals whatsoever. To give you an example, I put a set of Silverstones in my 1883cc 616 engine and it didn't feel right, was missing occassionally. Pull the plugs, we found the center electrode, not the prong, had fallen over and was in contact with the insulators. Put a set of Bosch copper cores on and it runs fine now. Not to mention, there as a 20hp difference on the dyno, but I think that's because the silver ones were not firing worth a damn.