View Full Version : Spark Plugs (from old site)

08-20-2004, 10:43 AM
This thread started with a question about replacing the spark plugs in a late model Tahoe and developed into a discussion of ignition theory. I have taken the liberty of editing out the Tahoe portions of the discussion in order to archive the theory portion. -D

Registered User
Posts: 9
(2/16/04 7:56 am)
Reply Re: Spark Plugs
I work at AutoZone and I'm not to impressed with the +4's. I have had more than one customer bring them back because they weren't happy with them. Bosch plugs are kinda weird some cars really like them and some don't. If it was my truck I'd put the original AC's back in. I've never had anyone bring back delco's and I've been at AZ for 3.5 years. Thank god only 4 more months of school and hopefully I can find a real job...

P.s. Hotter plugs will only help you if the plugs you have are to cold to efficiently burn the gas.


Edited by: JMitch19 at: 2/16/04 7:57 am

Unregistered User
(2/16/04 10:18 pm)
Reply heat ranges...
Ralph, it's been my experience (after much research on Dr. Jacobs) that there is not much to the actual "heat range" of a plug other than how much the porcelain tip is shielded which determines if it "runs" cooler or hotter-it relates mostly to how far into the combustion chamber the tip reaches. Remember the Golden rule regarding electricity as well-it follows the path of least resistance. Based on this, multiple electrode plugs are just a gimmick because if even one of the four electrodes builds up a fair amount of corrosion, then that is where the spark will fire-or "misfire" as it were. I've tried all plugs and the ones that work for me are ACDelco rapidfires and NGK's. Splitfires, Bosch Platinum +2's and 4's, etc. are just gimmicks. Platinum plugs offer more corrosion resistant materials so they will last longer but platinum does not conduct electricity as well as a copper core plug, either. I have yet to try the newer Iridium plug since they don't make one for my application, yet. As far as firing hotter spark, your ignition system (or control module, etc.) determines how much of a spark to give and how long the saturation is and so forth. The best thing you could do IMO is to go with the standard rapidfire plugs for your Tahoe and invest in a low resistance set of wires like MSD Superconductors (about $80), Taylor 409 race wire (around $100) or Jacobs Ceramic Boot wires($160+). These will give you FAR more spark energy and you should feel the difference right away! -G

Registered User
Posts: 135
(2/17/04 11:15 am)
Reply ignition system stories
Time to sort fact from fiction

Direct quote from heywood, concerning tests on "high energy" (higher current, longer duration): "The results of these studies show that away from the lean or dilute stable operating limit, increasing the discharge current or duration has no significant effect on engine operating characteristics. The higher current does, as would be expected, result in a larger flame kernel during the inflammation process and therby modestly reduces the spark advance required for maximum brake torque with a given combustion chamber and set of operating conditions."

Therefore, if you change plug wires or install a high energy system and feel a difference, then that means something else was wrong. Either your plugs were partially worn or fouled (yes, heat range does make a difference), or your old wires were shot.

Similar things can be said about bosch platinums. The smaller tip and wider gap extend the lean limit of the engine, but won't make a big difference under normal operating conditions.

Stronger ignition systems only serve to extend the sevice cycle by continuing to operate when a standard ignition system would begin to misfire. If everything else in your car is good working order, benefits will be minimal

So don't spend $200 on plug wires, and $5 a plug.

Unregistered User
(2/17/04 10:02 pm)
Reply RE:ignition system stories
I'm not sure who heywood is but according to Dr. Christopher A. Jacobs here are some excerpts from his book detailing a couple of ignition aspects. First, as far as a higher current resulting in a larger flame kernel Jacobs mentions, "If the spark is too intense, it actually pushes the fuel molecules out of its way, much like lightning pushes air out of the way followed by thunder. In cavitating, no fuel is ignited." Then, here is an interesting take on coils: He states, "For any given coil, the output spark voltage will be proportional to the amount of current (magnetism) flowing in the primary at the moment of interuption. Because it takes so long for current to build up, the output spark voltage goes down as engine RPM goes up. Higher engine RPM means more frequent sparks which mean less build-up time. Once you reach sufficient RPM where the coil primary current is interupted so frequently that the core doesn't have time to saturate, from that RPM on up, doubling engine RPM cuts build-up time and spark voltage in half. It feels liek the engine is starting to float or hold back. As current flows from the secondary windings into the spark, it generates negative, or cancellation magnetism. Negative magnetism is proportional to the number of secondary windings. So, it is spark current that ignites gasoline. But if you don't achieve arc-over voltage, no spark current will flow and you get a misfire. Required arc-over voltage is proportional to sparkplug gap. The bigger the gap, the more voltage you need to arc-over. But big gaps give a smoother running engine with better mileage and more power. For this reason, engine designers liek big gaps (about .100 would be ideal) but coil designers like small gaps because it allows them to use less secondary turns."
So what does all this mean to me? Well, it illustrates that you want the biggest plug gap as possible (up to .100) and to do so requires a higher energy ignition system (coil, module) to allow you to produce a lot of voltage which generates spark current at the plug-and ideally you want all this current going through a set of wires which feature the lowest rating of resistance you can find. Ah, but then to prevent having too big of a "flame kernel, or flame front" you can then open up your plug gap-which is dependant on engine modifications. So to me, this all works together as a system and it does play a major part on engine characteristics. Using a higher end plug wire is more than "extending the service life" of an operating system-come on-you can't honestly believe that? I mean, how can you claim that benefits would be "minimal" if you were going from a plug wire exhibiting upwards of 10,000 ohms of resistance to a wire giving you about 60-80 ohms at the same length? Maybe that would be the case if that were ALL you did, but again ignition systems are just that-systems....you need to upgrade the entire package. It's just scratching the surface but there is a LOT MORE to ignition theories if people want to poke and prod a little more.... -G

Registered User
Posts: 137
(2/18/04 10:45 am)
Reply who is he?
John B. Heywood
Professor, Mechanical Engineering
Massachusetts Institute of Technology
Author, "Intenal Combustion Engine Fundamentals", a textbook used in 100's of college level IC engine design courses (including mine) and often cited by professionals in the industry

Credentials aside

I did not clarify something: transistorized ignition is a worthwhile upgrade over points, which suffer severely from the charging problem you described, you are defintely correct about that. Even Electronic ignitions usually require an on time of 3-5ms though. This puts your RPM limit for full voltage at 3000-5000 RPM for an 8cyl. HOWEVER, do you think manufacturers did not realize that? They did! That's why, even though you didn't know it, secondary voltages are already excessively high at low RPMs to compensate for the loss in charge time as frequency increases.

Otherwise, the points Mr. Jacobs is emphasizing are all partial truths. Yes, wider gaps, higher current, etc can help...TO EXTEND THE LEAN LIMIT. They do not make more power. For richer mixtures and timing closer to TDC (IE closer than 35 deg BTDC) effects are minimal. So yes, your 80 ohm wires may help your idle when you run a ton of cam with huge amounts of overlap and hence heavily diluted cylinder charge. They may also help you if you want to calibrate for a lean cruise, which most people do not do.

Also I said a larger initial flame kernel, and I believe what you are talking about is a more intense arc. They are different. And even then, I'm not sure what he says is correct, since Mr. Heywood seems to be suggesting that the more intense arc leads to a larger flame kernel. But even if he was, unless you actually opened your gap to 0.100, well guess what? The 80ohm wires and 80,000V ignition system you have is gonna give you exactly that, a more intense arc. So, therefore, you should be responding about your dramatic decrease in performance since your super hot spark is blowing all the fuel away!

Even according to Jacob's own logic, you should aim for just enough power to achieve ignition. That minimum power can be correlated to things such as plug wear, cap wear, plug gap, electrode tip dia, electrode configuration, etc. The worse everything else is, the higher the secondary resistance, the higher your secondary voltage needs to be to overcome that resistance.

Like just about everything else in this hobby, ignition systems follow the myth that bigger is better, when the truth is bigger is overkill. Remember in 1993 when you "had" to tub your car for slicks, becuase bigger tires are better, and everyone knows that, even though those tires are being driven by a near stock 327? Don't laugh, I've seen it! At a certain point, going bigger doesn't help anymore, and it can actually start to hurt becuase you'll be replacing caps and rotors more and more often

I stand by my original contention: Hotter ignition systems (low resitance wires, goofy plugs, super high voltage coils) will not increase the performance of most people's cars. If it does, something else (crappy points, fouled plugs, rotten plug wires, wrong mixture) is what you should be looking for. The exception is when you have dramitically increased the redline to a point where the stock system really does run out of time, this again I agree you are correct about.

Registered User
Posts: 138
(2/18/04 11:11 am)
Reply web search
I did a web search trying to find a site that proves that low resistance wires will increase hp, and all I found was a reference to circle track article (see below) saying that no increase could be found.

I'm not saying hold on to your ancient OE POS 100k wires, no sense making things MORE difficult.
All I'm saying is this:

If you can buy a set of Taylor wires for $45-55, thats all you'll ever need. And if you can buy AC rapid-fires for $1.99, that's all you'll ever need as well. More than that is money down the drain.

Moderation, people.

www.nightrider.com/bikete...ires.htm#5 (http://www.nightrider.com/biketech/faq_ignition_wires.htm#5)

www.nightrider.com/biketech/truth.htm (http://www.nightrider.com/biketech/truth.htm)

"5. How much extra horsepower can I expect when I fit Magnecor Race Wires ?

Professional race engine preparers do not use Magnecor Race Wires to increase engine horsepower they use them to maintain full engine horsepower. Often, production vehicle owners comment that engine performance increased after they fitted Magnecor Race Wires, and most owners of modified vehicles find that horsepower increases during a dyno test however, in reality, performance increases because the engine's potential power was previously restrained by:

(1) Failing conductors in original equipment ignition wires;
(2) Failing conductors in aftermarket carbon conductor and European and Japanese spiral conductor ignition wires;
(3) Failing resistor-connectors on German ignition wires;
(4) Aftermarket spiral "low-resistance" and "super conductor" ignition wires interfering with the engine's electronics;
(5) So-called "built-in capacitor" ignition wires inducing too much available current to ground straps and interfering with the engine's electronics.

Despite what is published in advertisements and some vested interest magazine articles, no spark plug wires will generate or "install" additional horsepower. However, a decrease in horsepower will occur if the wires' conductors fail to conduct the spark energy needed to fire spark plug gaps, or EMI emitted from spark plug wires causes the engine management computer to react abnormally, or so much spark energy is lost into the ground straps of so-called "built-in capacitor" wires that little is left to fire the spark plug gaps see recent test in Circle Track Magazine (USA), May, 1996 issue. For these reasons, Magnecor Race Wires are used by many successful race teams and individuals all over the world to eliminate the risk of such events occurring."

Unregistered User
(2/19/04 5:59 am)
Reply partially speaking...
The partial truths DR. Jacobs speaks of are found to be the culprit of 60% of all field tested performance applications. Weak ignition-not other, unrelated problems-are the primary reasons for "unseen" performance capabilities-not other problems that a stronger igniton system is trying to mask. I don't doubt your professors' expertise on the internal combustion engine but as far as credentials, Dr. Jacobs holds the most patents worldwide for ignition performance systems and was employed by many of the top NASCAR, and off-road race teams as a consultant. But, the point is that if one were going to start analyzing and building a perf. ignition system, I would start by studying the work by someone who is at the top. Damn, here I go again rambling.... Regardless of everyone's theories, a lot of it (ignition) can't be observed to see what's actually going on but one can measure the effects between one system and another, for example. I don't doubt your professor has a significant amount of field research....I always have a reason for deciding or recommending one thing or another but I'd like to ask-just for comparison, what would your professor think of as an ideal ignition system-from what's currently available on the market? I like to see what credentialed people have to say as well as people with practical experience. Good conversation we have here. -G

Registered User
Posts: 140
(2/19/04 10:47 am)
Reply Good question
Unfortunately, I can't speak for him.

***Note*** I just finished this, and

Again, the topic has shifted slightly. The origin of the post was a Tahoe, and I thought we were trying to stick with basic street driven machines.

I forget that the idea of a street driven machine is vastly distorted in this forum! If you were to ask a "man on street" mechanic how hard it is to build a 750 hp "street" sbc, naturally aspirated no less, he'd say no way. If you ask it in here, you get "no problem, $6k should do ya, go for it!" The man on the street became a huge minority!

As we begin talking about racing engines (or P/T "street" engines) where compression ratios are going through the roof, fuel properties are changing, etc, then requirements change! Yes, you are absolutely correct if you are thinking that a stock ignition system will not do so well on a 9000 RPM, 14:1 engine. But the same design logic still applies: You work your way up until you have enough spark intensity to ignite the mixture, reliably and consistently, at WOT and max RPM (max torque rpm should also be checked). You do not then CONTINUE to add tons spark energy in the hopes that you will gain a huge amount of power. Maybe you'll eek out a couple more hp by capitalizing on the reduction in MBT timing as described by Heywood. Or maybe you'll see losses due to the phenomena described by Jacobs. Either way, it won't be much, and it'll probably be evident pretty quickly (ie not too much more current will be required). See what I am getting at? There is NO one ideal ignition system for every car, but there IS a very similar approach. Likewise, as with most everything else, what belongs on a race car does not always work on a street car. A nascar engine would not make a good cummuter!

You are right to question practical experience. Have I worked on a nascar development team? No. I respect Mr. Jacob's experience and expertise. In fact I have great respect for all hands-on, down and dirty mechanics and hot rodders that created this field for us. My father is a great inspiration for me, and my degree certainly has not handed me the wealth of knowledge he has in his head.

However, I have also found that a great many of "givens" in this hobby, though actually true when they first applied, no longer hold much water today. Yeah, when people upgraded their model A roadsters from copper strap conductors to resistive plugs and better wires, they found a noticable increase in power. And, when people were able to replace points with electronic "high energy" ignition, things leaped forward again. But, what has happened is that the "if a little is good, more must be better" mentality works in. My dad is a firm believer that his 80ohm/foot msd wires are better than my 1k/ft taylors. I disagree.

Part of the reason for this is that vendors continue to market the old ideas. Perfect example: the tornado! For carbureted cars with poor vacuum signals, the idea of swirling and mixing the intake charge had some validity. But does it have any place on an SEFI car? No way! But they continue to play off of the 50 year old "common knowledge" that you need motion at the throttle body to get a homogenous charge.

(coming full circle here, finally) Is Dr. Jacobs part of this problem, now that he is in the business realm? I dunno. Again, I think the things he has learned are totally correct, for his application, but I think saying that the same lessons apply to a 300hp 9:1 engine is not as correct. I think the things that I say, and the words that I have quoted from Heywood, are more geared toward "near stock" (less than 500hp).

I can totally ramble with the best of em.