Can anyone tell me if they have ever heard of this. I was running base (non-plat) autolite plugs in my 1988 F350 351w EFI 4x4. It was time to change the plugs so I put in Autolite platinum plugs and it has had a miss at light acceleration ever since. I was chatting with my buds and one of them said that sometimes the plugs can be too good. Is there any truth to this, too little resistance, whats the deal. If anyone has heard of this let me know. I think I am going to change back to non-plat plugs, can't hurt and only cost a couple of bucks. If this is the case I am glad I didn't buy the quad-plat plugs!

Thanks
JPF

 

no, plugs can't be too good, if the resistance was low, then you would have extra current through the gap to produce a more wicked spark. Remember Ohm's law, V=I*R, your ignition will supply the voltage from the coil, and if your resistance decreases, this will make the current rise to match the voltage, and more current=more spark. Your '88 is not equipped with an ignition system that can take advantage of platinum plugs. The discovery I made is that if your engine is not originally equipped with them, then they will never be able to take advantage of them. I thought my MSD would like Bosch's platinum plugs, but they actually perform worse than Motorcraft plugs. I've heard that NGK u-groove plugs are the best, I'm going to investigate that soon, I'll keep you posted.

Happy Wrenching,
Cadet Second Lieutenant John F. Daly III
South Carolina Corps of Cadets, The Citadel
The TorqueKing

 

"if the resistance was low, then you would have extra current through the gap to produce a more wicked spark"

Lieutenant, You have the right formula, but in this case your concept is a little off. The ignition system will provide voltage (up to its maximum capability) necessary to arc the spark plug gap. If the plug gap is too close (low resistance) it will arc at a lower voltage with a weaker spark. A stronger spark can be obtained by increasing the gap (higher resistance) to allow the voltage to build to a higher level before arching the gap. Stronger spark. Of course if you make the gap too wide, the voltage will not be sufficient to bridge the gap.(No spark). An old farmer's trick was to cut the plug wires and introduce a gap so that the voltage would be higher for a better spark to prevent plug fouling and a better running tractor.

Good Luck in your studies, keep thinking, keep talking, but don't forget to listen.

 

It is very important to have the correct gap with Ford Duraspark ignitions. Most spark plugs come pre-gapped at .44-.46 which is too small, leading to a weak spark. Always use the underhood sticker, not the spark plug catalog. Usually, Ford calls for a .52-.56 gap.

I have had excellent results with Bosch platinum on 2.9, 4.0 and 5.0 Fords. The Autolite platinums I tried did not last 30,000 miles. The ground electrode was almost gone!

Jim

 

I agree that voltage is increased with the plug gap, voltage is simply described as "potental difference", the mechanical equivolent to elevation. I've heard two opposing schools of thought on this; one says that the wider the gap, the longer the spark, therefore more contact with the air/fuel, the other supposedly comes from the strip, there in ultra-high compression environments, the resistance is greatly increased through the gap, and it is better to undergap the plugs to have more current, or a hotter spark. The latter doesn't make as much sense, because to get more power, or heat out of a spark, you have to increase voltage and current, since power=I*V. It would make sense that increasing the gap increases the potential difference, but only so long as there is sufficient current to jump that gap. I'll have to read further into this, but I think I like what you said, it makes more sense. I apprecite the discussion, it would be no fun if we all just took each other's word for it.

The TorqueKing

 

It sounds counter-intuitive but bigger gaps means hotter sparks. The sparks come from an inductor, a coil. Actually, it is a transformer, a very large step transformer, that converts 6 or 12 volts to 20,000 volts. The coil generates this spark when the primary current is interrupted.

Air has a pretty decent dielectric constant; it takes some pretty good voltage to arc through air. If you have a small gap, less voltage is required to cross the gap. The spark will be smaller, and last longer. If the gap is big, the spark will be bigger, hotter, but its duration is shorter.

Big gaps means larger voltages. Larger voltages in the secondary ignition means more likelyhood of induced current in parallel plug wires, arcing through the plug wires to ground, carbon tracking in the cap, ozone in the cap (which is hard on the points and other exposed metal), and shorting through windings in the coil. Basically, all this leads to random misfires.

Ya pays yer money and ya takes yer choice.

I'd be more inclined to fool with choices in plug design than with the gap. I've had some really good results with using extended tip plugs.

 

but if all your gaps are wide, then why would the spark crosfire, since it only crossfires to find a path of less resstance, right? Then it would take a great deal of voltage to jump into an adjacent wire, then make another jump to ground through that cylinder's plug, or back through the distributor gap. I appreciate the insight, are your an electrical engineer? I always thought of a coil as only an inductor, and when the primary circuit changes current, the coil responds with a violent voltage spike, as voltage across an inductor is proportional to the change in current, I wish I could use alphas and derivatives, but I found out earlier you can't paste MathCAD worksheets on here. It's definately a good idea to use a transformer with a coil, to step down the voltage, resulting in a huge current gain on the other side, which makes the inductor react even more violently. I'm fresh on this stuff, I just took Electricl 308, circuit analysis for engineers, but non-EE students. What is the maximum plug gap that I should use, I've always been fine with the factory .044", but I guess I should look into opening that up a little bit (or a lot). I'm going to buy a set of NGK v-grooves, I've heard they are the best, I'm waiting until I get my MSD street-billet distributor, so I don't ruin them with little or no advance that my Duraspark distributor gives me. Don't worry, I'm all MSD, 6A w/Blaster II, I jsut kept the factory distributor, which remains the only thing under my hood that was installed in Dearborn MI. Keep up the info, I really appreciate it, Rock on!

The TorqueKing

 

[updated:LAST EDITED ON 19-May-02 AT 00:16 AM (EST)]Not an electrical engineer, but an electronic technician who's been through two different schools. The diaelectric constant of air is pretty big. Open up that spark gap and the coil doesn't fire until it's got a healthy jolt to deliver. But don't take my word for it, pull a plug on a cylinder, open up the gap pretty good and run that engine at night when you can see the voltage leaks and cross-fires under the hood. You'll see little blue lights around the wires.

The coil is a transformer. There's a primary winding and a secondary winding. Note that there are three wires attached to a coil; a little + wire, a little - wire, and a great big fat wire. The primary and secondary sides of the transformer share the same ground. When you first run the juice from the + side, the inductor reacts with an opposing voltage until the windings build up a magnetic field. Once the magnetic field is created, the current can flow through the primary. When the primary circuit is interrupted, there is no current to hold the magnetic field, but there is a path through the secondary. As the magnetic field collapses it induces current in the secondary side of the transformer. And because of the ratio of windings, the secondary produces a much higher voltage.

Now think of the spark plug as a capacitor, one with air as the diaelectric. The voltage will build up on one side of the capacitor until it exceeds the diaelectric constant of the air. Then it will arc through the air. Note that I said it will build up. That means a delay.

Hope that helps.

 

So Paul, I got my NGK v-grooves, now how do I go about gapping them, and what gap should I use? That is great info on the reality of automotive circuits, I learned extensively how to analyze models, and less time actually dealing with real circuits. I'd like to get a nice, wicked spark, without arcing. I saw an HEI coil this weekend that arced under the cap, and it blew out the epoxy that seals the case, it was really unbeleivable. I'd not like for this to happen to me, so I'd appreciate your expert, experienced advice on how to setup my ignition to push the envelope of max performance, and electrical disaster.

Thanks again,

The TorqueKing

 

I'm no expert, but I do try to apply what I've learned about electricity and electronics, chemistry, physics, and computer programming, to cars.

I wouldn't suggest trying to amp up the ignition at all. Trying to turn the power up in the secondary ignition system can turn into a vicious circle; you'll need bigger wires, hotter coil, better rotor and cap, you're burning out plugs, and all you've done is light the fire a little sooner.

I do endorse the idea of MSD, Multiple Spark Discharge. Basically, it makes a nice long spark; less chance of misfire and it runs at stock voltages.

And I like extended tip plugs. I've had good results with them. They stick out into the chamber and they can get the fire started nearer the center of action. One manufacture's web site suggested that you may want to pull the timing back to help prevent knocking and get the full benefit.

 

so what gap and heat range should I use with an MSD 6A, and a Blaster II coil, and Motorsport 9mm wires?

 

Hey, TorqueKing...

I would run it at about .050 and see what happens...this is where it either becomes trial and error, or you have a dyno to keep resetting the gap until you get max hp/torque...but, for around a 10% improvement, keep the gap between .040 and .044 and side gap the protruded electrode which will expose more of the spark to the chamber...race car plugs already come side gapped and the NASCAR plugs use a 4 prong approach like the Bosch patinum 4s, only with a nice heavy electrode...

 

Yup. I surfed over to the MSD web site to research that part. They're putting out about 45KV so you can easily run .050 gap with your 9mm wires.

 

> Your '88 is
>not equipped with an ignition system that can take advantage
>of platinum plugs. The discovery I made is that if your
>engine is not originally equipped with them, then they will
>never be able to take advantage of them. I thought my MSD
>would like Bosch's platinum plugs, but they actually perform
>worse than Motorcraft plugs. I've heard that NGK u-groove
>plugs are the best, I'm going to investigate that soon, I'll
>keep you posted.

I have an 84 F150 351w and I put in MSD plugs and wires then I put in an MSD Coil and 6A, is this going to be allright for my truck or will they not be as good?

 

MSD Wires are sweet, I always like to talk about Motorsport 9mm wires (the ONLY Ford product I recommend), but that's because they're made by MSD, for Ford. Just like the roller rockers that you see in the display case at the Ford dealership? Yep, you guessed it, they're nothing but Crane Gold Race Rockers with a cool blue anodized finish, manufactured by Crane, for Ford. Same deal with 4.6/5.4/other mod motor cams, they are all made by Crane Cams, since Ford engineers couldn't figure out how to cam their new engines, so they hired Crane to figure it out for them, and mass produce cams for new vehicles. Go with NGK v-grooves, they sell them at Advance Auto Parts, and I am an AutoZoner, and I'll recommend you to that store, but only to buy NGK plugs, and not the platinums, just the regular, $1.59/piece. They are sweet, the center electrode is split down the center, not like split fire, which has a split ground electrode. I won't care to venture why this works infinately better than the splitfire design, but I will stand by it, and because Paul probably knows the real answer anyway, I'd just be hypothesizing. go to NGK.com, or whatever their address is, they have a good website, and they actually respond to your tech emails, so they can recommend a plug, heat range, and gap for you. You're gonna love that 6A box, it is the best bolt-on around, except maybe an Edelbrock 600 carb, but that's another topic. I am going all the way, I'm ordering a Street Billet distributor, b/c I'm sick of the misifiring, and lack of advance I get from my stock Duraspark dist. After this weekend, the only surviving Dearbone-created part left on my truck is going to be the coil bracket, but it doesn't really count, since I took a drill to it to make it bend to my will, and accept that blaster II.