Platinum Plugs and Ignition Systems by Ray Paulk <>


An ignition system is the entire package required to light off the fuel. The most interdependent components are the plugs and the coil. They must be considered as a system.


The stock coil on most cars is a compromise between cost and performance. They generally put out enough "juice" so the vehicle runs pretty good with a warm engine running up to mid-range RPMs. As a secondary cost vs. performance compromise, the factory usually installs steel-tip plugs with a relatively narrow gap. The narrow gap compensates for the weak coil helping to assure a spark at low coil outputs. With a cool engine or high RPMs, the coil does not have the power to properly fire the steel tip plugs. Studies by Jacobs Electronics have shown that stock engines generally mis-fire 3-5% of the time when warm and up to 20% of the time when cold. These misfires both waste fuel and potential power.

Basic Theory

When a spark plug ignites fuel, it starts a small fireball, known as a "kernel", which propagates throughout the chamber. Studies have shown that the ideal kernel size is .100 inches. With the same intensity of a spark, the power output from an engine increases as the size of the kernel increases, up to the .100". This translates into an ideal spark gap of .100". Unfortunately, this would take a coil the size of the engine itself to provide the required energy. Therefore, we must "play" with the gap vs. coil power to obtain the best performance for the system. For a given coil, if we start with a small gap, we only get a small spark. As we increase the gap, the intensity of the spark also increases....up to a point where the coil is no longer capable of generating enough voltage. For any combination of coil and plug, there is an optimum gap setting for the best results.

Platinum and Other Specialty Plugs

The advent of Platinum plugs and other specialty plugs, is an evolution in the search to find a plug which would fire more reliably than the normal steel tip plugs at a wider gap with the lower voltage output of a stock coil. It was discovered that by coating the electrode from which the spark emanates with platinum, the spark would ignite at a lower voltage for the same gap. Therefore, the gap can be wider than a steel tip plug for the same voltage. The wider gaps mean more power and improved fuel economy without loosing the relative spark reliability.

The compromise of the Platinum plugs is that they do fire at a lower voltage which inherently means a less intense spark which does not ignite the fuel well. Although the ignition kernel may be larger, the intensity is lower which makes it propagate slower. You get less HP from the fuel consumed.

It is well known that steel tipped plugs produce the most intense spark. Think of it as conductivity. The lower the conductivity, the lower the spark voltage for a given gap. How conductive is steel vs. Platinum? Before Platinum, I recall ads in Popular Mechanics about new and innovative copper core spark plugs. These worked well for a short time but unfortunately the copper couldn't withstand the spark and burned up fairly quickly. Coating steel with platinum counters this effect. Ideally, you want a spark plug with low conductivity combined with a coil large enough to fire it over a relatively wide gap. This brings us to the "super coils".

Super Coils

One of the best improvements one can make to the performance of your engine is to install an after market "super coil". You should get better fuel economy, more power and a much cleaner running engine. On the down side, stronger coils are bigger. The better ones, which really make a difference, no longer fit in the stock location. But on a Fiero V6, look at the stock location. Keep in mind that the worst enemy of a coil is heat! You want the coil in a place where it can dissipate heat quickly. Setting right on top of the engine is definitely not the best place. Actually, the best place in a Fiero engine compartment is on the side near the air intake. I mounted mine on the left inner fender wall just under the vacuum canister; it is cool and just a short jump to the distributor.

The Fiero 2.8L V-6

The Fiero version of the 2.8L V6, with its HO heads, presents a unique twist to the plug/coil balance. The HO heads "want" to ignite the fuel more that the regular 2.8. Therefore, the "rules" which apply to normal engines may not apply to the Fiero engine. The equation changes. For instance, in a normal 2.8 a gap of .035 might be optimum for steel plugs and .045 might be optimum for Platinum plugs. On the Fiero, these numbers might be .045 and .055 respectively. It may be such, if you happen to have a better stock coil, that the Platinum plugs may never perform as good as the steel plugs. This is unlikely, but possible.

My System, Experience and Opinion

I installed an entire Jacobs ignition system with an Ultra coil. I normally run Autolite steel tip plugs but recently tried some RapidFires which are steel tipped with a reduced area electrode. Since race car plugs generally have electrodes filed to a point for better spark, the RapidFire tip seems like the right approach. On the down side, the RapidFires have a preset gap of .045 with distinct instructions not to reset. What I gained in the reduced tip I probably lost in the narrow gap as I don't notice any change.

Initially, after installing the Jacobs system, I didn't see any improvement in MPG. I could feel better acceleration, but it only clocked a gain of .04 seconds in 0-60 time runs. Over a course of 3 months, my time trials gradually got shorter eventually knocking off more than 1/3 of a second. The idle improved as well as my high RPM torque. Via discussions with Dr. Jacobs, I was advised that my gradual time trial improvements were the result of the better ignition burning away the deposits within the combustion chamber and exhaust system. The engine was starting to run as designed. Recently I changed my O2 sensor and EGR valve. Both were very clean with none of the normal soot. In my last state inspection, the tester remarked that my car had the lowest emissions of any car he has tested (and this is a place which has them lined up out the door.) Of course he followed it up with "and this is a Fiero, they always fail!" which may have influenced his first statement. My system gives me a better performing, cleaner running engine. I haven't seen any improvement in fuel economy, but that may be because the more power is more fun to play with. A good ignition system can't compensate for a lead foot.

Bottom Line

Bottom line is that you must find out what plug works best with your coil. If you're looking to upgrade your coil, I suggest Crane, MTD and Jacobs in that order from better to best. In my opinion, the Accel coil is only a baby step better than stock and not worth the expense. If you are going to make a change, do something significant.


For further reading may I suggest "The Doctor's Step-By-Step Guide To Optimizing Your Ignition" by Dr. Christopher Jacobs, Jacobs Electronics, Midland, TX. Tel: (800) 627-8800.

The book put me to sleep several evenings, but it is thorough and gives one a good understanding of ignition systems. I was fortunate enough to have several long discussions with "the man" himself, Dr. Jacobs.


Ray Paulk


Our refresh-proof  hit counter reports: users since May 20, 1996.    

Copyright 2001, Northern Illinois Fiero Enthusiasts, Inc. All Rights Reserved.
Send Comments to Webmaster.

Fiero Focus Online is a publication of the Northern Illinois Fiero Enthusiasts, Inc. (N.I.F.E.).  No copies of any part of this publication may be made, distributed, and/or sold without prior consent of N.I.F.E.  "Pontiac" "Fiero" the Pontiac symbol, and the Fiero badge are all trademarked by General Motors Corporation.  N.I.F.E is not responsible for any/all information provided herein.  Any and/or all adjustments made or information act on are done at the sole risk of the individual