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Platinum Plugs?


Jun 23, 2001
Chester, NY
82 Red Coupe
Getting ready for the pilgrimage to Carlilse, I figured I'd tune the car. All these years I've used only ACs in my "babies" . . . sometime Autolites in the others.
Just had a problem with my daughter's Cavalier, where It just started running like @#$%. Found an arc in one of the wires, so I replaced all 4. The car ran slightly better but was backfiring through the TBI. Checked one of the Bosch Platinum plugs and it looked OK--but my trusted mechanic checked the other three to find that they had "self-destructed". After only 20K!! Put the standard ACs in and the car once again runs perfecto. Prior to this I thought maybe Platinum was the way to go for the vette ('82). Now . . . never again. Any body had similar problems with Platinum plugs? What about the AC Rapidfires--any body recommend them?

BTW, now, to further complicate things, my understanding is the new Rapidfires are Platinum--at least that's what my AutoZone guy told me.
I had this discussion with my machine shop mechanic who has done a lot of dyno testing of sparkplugs. He informed me that these fancy plugs do no better than regular quality plugs and in many cases performed worse on the dyno. He suggested Autolite plugs when I switched to vortec heads as they did best on the dyno. Just my .02 worth.


Bosh Platinum in the '81 Vette, 99 Dakota, 94 Grand Cherokee. Never a problem, always look good even after 30K. Heard lots of good about the AC Rapidfire....haven't tried them yet.
Ahmen80 convertable, If it says it came with AC R44TS.........That's what I put back in. I have had soooo much trouble with split fires, accells etc (Dale is the only person that I know who can afford that many Bosch Platinums :s)..................Steve
My son and I put a new engine in his old Bronco II.We put new platnium plugs in the new engine along with everthing else like wires etc. We fired her up ok but decided to drive down to the auto shop down the street to get it checked over as we don't know much about fuel inj etc. The first thing the mechanic did was take out the new platium plugs with about 2 miles on them and throw them in the garbage. Then he installed old plain jane ones, and adjusted a few things and said it was done. I asked why he threw them out and he said to prevent problems.

I dunno maybe he just wanted to sell me plugs but I don't really think so.

The primary advantage of platinum plugs, especially when used with an OEM ignition system (particular with an older system, which may not be producing as much voltage as when it was new), is that platinum will require less arc-over voltage and thus allowing allows the gap to be jumped a higher percentage of the time.
For example, if at factory gap and with steel electrode plugs, may require as much as 18,000 volts five percent of the time to jump the arc. This will be due to the changing engine environment and running conditions. So if the OEM only produces 17,000 volts, then it follows that five percent of the time there would be a misfire.
If platinum plugs are installed, which may only require, 12,000 volts to arc-over, the five percent misfiring with steel plugs would be eliminated. Since the ignition output on OEM ignition drops off as rpm increases, platinum plugs would allow the motor to turn higher rpms giving and increase in performance and maybe gas mileage as well.
The disadvantage of this method of reducing misfires is that the higher arc-over voltage, the better the spark when it does fire. Therefore, platinum plugs will show a performance improvement with a weak ignition because the benefit from reducing the percentage of misfires more than outweighs the loss from reduced spark power. If you have a healthy ignition system, a higher arc-over voltage will produce a higher energy spark when it does fire since it is at a higher voltage. So for max power one would want a good robust ignition system with plugs that have a high arc-over voltage. Translation, good old regular plugs.
SplitFire (split electrode ignition) plugs also reduce the amount of arc-over voltage, but they do this in a different way. Rather than using a different metal as the platinum plugs do, a V is cut into the ground electrode, thereby giving three more "pointy" areas for the spark to jump from. It is this increase in the number of pointy areas available to the electrons migrating from the center electrode to contact which lowers the arc-over voltage. All the advantages and disadvantages of platinum plugs described above are inherent with the installation of SplitFire plugs.
While certain geometry's of electrode design, such as splitting the ground electrode, have gained popularity, the principle behind all unusually shaped electrodes is virtually the same. That is, spark likes to jump from and to pointy objects. Therefore, the sharper the point of an object, the lower the voltage to arc over.
This is why newer plugs often increase miles per gallon and performance: the center and side electrodes are cut sharp, but after being used for many miles, the constant flow of arcing electricity invariably tends to round them off.
Surface gap plugs, which provide a solid-state medium for the electrons to migrate across, generally allow electron flow, regardless of spark voltage. However, they do not allow the air/fuel ratio 360 degrees of contact area with the migrating electron as is accomplished with an open gap type spark plug, but rather only 180 degrees. This is because 50 percent of the electron path is shrouded in the solid state medium. Like platinum and split electrode ignition plugs, they mask a problem inherent in weak ignitions.

Over the years I've tried platinum plugs in various engines and everyone ran crappy right off the bat. Trashed them. Few years later tried again in different rides. same result. Platinum has the reputation for requiring a really hot ignition. I gave up and stick with the AC.
C5phil, thank you for the tutorial.
You could put a few drawings or pictures with your responce and submit it to the Technical help section.

Thanks for the kind words. I am pleased if my rambling was of any use to you.

Platinum Plugs

Great write up on the technical end. I'd like to add just a few comments if I could to help those may not have made the connection to some of what was said. Platinum is a much better conductor than iron, or copper, two metals used in the plug core. As a result there is less resistance, less voltage loss, and less heat generated. Simply put platinum runs colder than a conventional plug and is more likely to foul under some conditions like frequent short trips with no long trips ever. The up side is the spark is stronger and ignition is more instantanous and combustion is more complete. This should equal more horsepower and better fuel economy. Also I have learned that using silcone grease on the plug boot is the best thing since sliced bread. The boot slides on and off easily, is sealed water tight, and practically gurantees that the connector sliped on over the plug correctly. Also setting the correct gap is critical. Different applications require different gaps even on the same plug. Installing them fresh out of the box is a BIG mistake, they are never and I mean never all gapped the same or even correctly. Sometimes when only the plugs are changed and nothing else, ignition systems seem to mess up. I've always had the best luck when I change the plugs, cap, and rotor together. Every 60000 miles I change the wires too. Steve.......Champion Plugs .99____Bosch Platinum $1.50, yup I can afford it for the increase in fuel milage and power.
Is that all, I really thought they were more expensive then that................But, they still ain't AC (I think the last AC's I got was close to, or over 2.00).......It's bad to get old and stuck in your ways:( ..............Steve

I apologize for the length of this post and that I am probably beating a dead horse. However, I wanted to make
certain that I was clear in that platinum plugs will usually not be desirable if your goal is max horsepower in a well maintained vehicle. Nor the best gas mileage.

Specialty plugs work by reducing the amount of voltage required to jump the spark gap, thereby making it easier on a weaker ignition. The amount of voltage necessary to achieve arc-over at the electrode gap is set by the following characteristics:

The size of the gap, where arc-over voltage is approximately proportional to gap size.
The air/fuel ratio within the gap, the richer the lower required arc-over voltage.
The compression at the moment of arc-over is to occur, the higher the compression the higher the required voltage.
The composition of the electrode, different conductors have different arc-over voltage requirements.
The shape of the electrode, the sharper and more jagged the shape the lower the arc-over voltage.
The amount of fouling deposits trying to remove electron flow from the arc (they do not actually raise the
arc-over Voltage, but make the ignition work harder to reach it.

While it may therefore seem desirable to lower the required arc-over voltage, since without arc-over there is a total misfire and no ignition, low arc-over voltage produces low spark power because spark power is directly proportional to the square of arc-over voltage. That is, by doubling the required arc-over voltage, you quadruple the instantaneous peak spark power and the higher the spark power, the better the fuel mixture ignition.

Platinum plugs are more likely to reduce power when combined with a good electrical ignition system due to the reduced energy in the spark.

Jacobs Electronics, as an example did some tests and have noticed an increase of power using specialty plugs, on some occasions, with weak ignitions. However, they never saw an advantage to using specialty plugs with the good strong ignition systems. In some cases, they saw a slight loss of power when specialty plugs were installed in place of standard, steel electrode plugs at the same gap.
However, they saw a gain with specialty plugs when their lower arc-over voltage requirement has allowed an increase in the plug gap above that possible with steel electrode plugs.
Testing a 253 cu. in. V-6 engine, which was slightly modified, with the factory recommended .045" (1.14 mm) spark plug gap. With the stock ignition in place, it produced 168 horsepower. They installed platinum plugs gapped at the same .045" and the horsepower increased to 171. Then with Split Fire plugs, the horsepower stayed at 171. With surface gap plugs, the horsepower rose to 172.5.
Next with a high-energy ignition system, reinstalling the original steel electrode plug gapped at .045" and the horsepower increased to 180.5. Keeping the gap a .045", we reinstalled all three sets of specialty plugs, recording an average 1.5 - 2 horsepower drop from the 180.5 recorded earlier with the steel electrode plugs.

The reason for this power loss was that the specialty plugs required less arc-over voltage at the same gap; therefore, the peak spark power fell off.

Just wanted to make clear that with a good high energy ignition system working correctly, one can usually expect the highest horse power with standard steel plugs (perhaps even clean old ones).

It may be that your increase in hp and mpg is due to a weakness in somewhere in your ignition system.

OK C5 phil, now that I know, way more then I thought ever possible about spark plugs..........Are you saying that, with a good ignition system, proper compression, and properly tuned engine, the original spec (AC DELCO) plugs will work better? The spark plug war is very similar to oil or oil filters, etc. I just prefer, what they came with. I know that there is better filters then AC, but I think the AC filter looks better then WIX. Now, I am talking about retored, sometimes shown cars. Not your daily driver. I feel the same way about the "few" Mustangs I work on. I wouldn't put an AC filter on a Ford, it would be Motorcraft, etc. I have judged a few shows, and these were one of the 1st things I looked for, especially when the judging started getting tough.........Steve
For those of us who, for years, have thought a "plug is a plug",C5Phil and DDL-81 have certainly given us an education. Thanks! Funny (maybe not)how these marketing people are able to convince some of us that even though the car is running good . . .it will run even better with the "new improved" (read that more expensive) version. I've NEVER, in 32 years had a problem with an AC--but hey, I thought I'd be doing the vette good by installing the "best". Thanks for the info, guys--and the straight forward, technically reserved way you got it across.
DADS8T2 said:
...marketing people are able to convince (us)

Remember P.T. Barnum's phrase
"There's a ****** born every minute."

I like the commercial (see that? I'm a ******! :L) where they show the plug with about a zillion tips! :Silly


Yes, with a good high energy, properly working ignition system you will get a more intense spark from steel plugs.

It is as if you filled a balloon with water the longer it takes to burst the bigger the splash when it does go. The voltage at the gap is proportional to the number of electrons that build up there, the more electrons the more intense the spark when the dam does burst.
Steel having a higher arc-over voltage than platinum, allows more electrons to accumulate before the voltage is high enough to jump the gap, thus a “hotter spark”. Specialty plugs can have their applications, but if your goal is the most power and you intend to keep your engine and component systems in top conditions steel plugs will be what you want in almost all cases.
The same is true for split-fire plugs since they arc-over at a lower voltage than single ground electrode plugs.
With a poorly operating ignition system, platinum or split-fire plugs (since they fire at a lower arc-over voltage) may make the engine run better. Still, this is masking the real problem. This is the reason that platinum plugs can remain in a vehicle for extended periods. As they foul or other parts of the system degrade, the platinum plugs continue to fire keeping the engine running smooth. However, this does not lead to the highest power.

Sorry, as always about the length of my rambling.

Thanks for the in depth info. It's hard to dispute dyno comparisons between platinum and steel. I'm going to try a set of AC plugs in my 81, as I mentioned the ignition is all new, wires, cap, coil, and ect. Heck, she might like them even better!! :w

It will be interesting to see what happens. Not forgetting that, plug indexing, heat range, extended tip or not, and gap size can alter the plugs performance. In addition, when any plugs are new most machined or stamped edges are very sharp, this will lower the arc-over voltage. You will need a few miles on the steel plugs for the spark to erode away the very sharp edges before they will rise to their highest arc-over voltage. If it does not run equal or better, and we cannot find another cause, I will send you a set of platinum plugs of your choice.

I don't know about Hi-energy ignition systems and what not. I've been using Bosch Platinum plugs since they started selling them. I've put them in about 8 different engines/cars and have never had one foul. Can't say that about any other plugs I've used. One set of Platinums is still in a '89 350 with about 70,000+ miles on the set.

When I have an ignition/drivability problem, I'll check the plugs last....so far I haven't had to

Maybe I just got a couple good batches.

I would say that you probably did not get a "couple of good batches", the platinum plugs you purchased have worked as designed. I am bit lousy at explanations, so please bear with me.
Platinum plugs will continue to fire under circumstances that others will not. This might be equated to "never fouling". This is what platinum plugs were designed for, longevity and better spark under adverse conditions. What they were not designed for was Maximum Power in a well-maintained performance engine.
I run platinum plugs in my C5 for the same benefits as you. Still I believe that they do not produce as much power as steel plugs. The difference to me does not outweigh the benefits of the platinum plugs. But, if I were concerned about a 100th of a second you can bet that it would be good old American steel plugs, indexed, bead blasted, and all of the other almost anal incremental improvements I could employ. Life is full of choices; there is no “Perfect Plug”. One must choose what they want as an end result.


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