Can I go with 0.040'' Spark Plug Gap? [Archive] - Classic Cougar Forums

: Can I go with 0.040'' Spark Plug Gap?



wout67cat
December 24th, 2006, 07:56 AM
My Setup:
- Accel Supercoil + ballast (original ballast wire also still inplace)
- Pertronix 1

I have read some threads about it and some seem to go to 0.045'' without trouble. As this is a daily driver I aim for a compromise between 'better than stock' and ''troublefree''. So is 0.040'' ok for this setup?

:wave:tnx & merry Christmas:wave:

wouter

Royce Peterson
December 24th, 2006, 02:55 PM
The Accell Super Coil and Pertronix combination won't offer any extra ignition energy. If you added an MSD box or something similar that would boost coil input power then you would have more energy and could open the spark plug gap some. But as it is now you will have best results with .035" gap.

xr7g428
December 24th, 2006, 04:08 PM
Exactly which Accel super coil do you have?

What you are asking is a very complex question. A wider gap requires more voltage for the spark to jump. More voltage equals more heat. More heat is a good thing. However, the compression ratio and the fuel mixture have a lot of influence on how much voltage you need to jump any particular gap. So the real answer is that you can try a wider gap and see what you get.

The basic ignition system in your Cougar uses the coil to increase the voltage like a transformer, and also to store power in the form of a magnetic field. When you add a capacitive discharge system like the MSD, the storage of the power is done by a capacitor, and the coil serves as a transformer to bump up the voltage. Capacitors charge very rapidly, so at low RPM it is actually possible to fire the plug more than once per ignition cycle. Hence the name Multiple Spark Discharge. So the MSD is going to do two things, increase the voltage, and also fire the plug multiple times. More voltage equals more heat, and multiple sparks tends to keep the plug cleaner, and insure complete combustion.

Most high performance coils do produce a bit more voltage, and also store more energy, but not in the same league as what an MSD would give you. In my limited experience, you can increase the gap in a street car when you use a higher output coil. If you have built the engine for higher compression, or higher rev limits, then you probably are less likely to be able to increase the gap. You may need the high performance coil just to get it to fire properly with a stock gap.

Keep in mind that anything you do to increase the spark is only going to be helpful if you have a good cap, rotor, wires and plugs. Do the basics before you try anything else. If you are going to use it, make sure your original coil is in good shape.

So, in order of importance, in my experience, get the spark to occur at the right time, every time and eliminate dwell issues via electronic ignition, like the Pertronix. I have yet to see a 35 year old distributor that didn't have some wobble or other issues. The Pertronix seems to fix most of these problems. Next, add the MSD box IF you are building a high compression, high revving, motor. Keep in mind that you might have to further upgrade the wires, cap and rotor.

There is a point of limited returns. Twice the spark won't make as much difference as enough spark.

Good Luck!

greggieatthebat
December 26th, 2006, 04:24 PM
Slight twist.
So, with a 302 with 9.0:1 (I think), 272H cam, and stock heads, what gap should I run with Autolite 45s, MSD 6AL, and Accel Super Coil (8mm accel wires). Right now I'm running 0.032 or 0.035 I think, but I haven't put the MSD on it yet.

And when I switch to the GT40 Cobra (iron) heads that recommend 0.053 on the platinum plugs, what then? Can/should I run platinum since I will be running the hotter (MSD/Super Coil) ignition? Or is copper still better? I know the rare metals like paltinum and titanium require better ignition, but do I get anything out of that other than longer plug life?

wout67cat
December 27th, 2006, 02:22 PM
Allright thanks gents for the answers sofar. Still some questions though :confused: (I do believe but also want to understand).

The coil I have is a ACCEL 140001 + ballast resistor. Dizzy is a remanufactored one (autolite?). Spark plugs & cables half year old. Car is driven every working day (but for the coming 3 months as it has gotten colder and they are putting salt on the roads). It has proven very reliable sofar (but for a rear shock coming loose). High-revving is not the intend.

My line of reasoning (sofar) was as follows:
- higher voltage (super coil) means possibility for the spark to jump wider gap
- wider gap means 'longer'' spark
- longer spark means 'more complete' combustion

From what I hear I should lean more towards spark energy? Energy being Volt X Amps, the super coil ups the Voltage but lowers the ''current''. So total energy of spark remains appr the same? So what does the high voltage help with, more reliable spark (because it always jumps)?

Any good book recommendation on this stuff would be appreciated (I already bought ''How to rebuild the small-block Ford'' but it does not dwell [LOL] on sparks & ignition.)

greggieatthebat
December 27th, 2006, 04:27 PM
The coil you have is the big rectangular one, right?
That will give you more voltage at the plug which should allow either fatter spark with same gap or similar spark with larger gap.
The larger gap potentially keeps the plug cleaner (I think) and creates a better flame kernel for better combustion (I think).
Newer cars (that I've seen anyway) have a lot more voltage to the plug (either with HEI or MSD style ignitions or individual coil packs right on the plug) and also large plug gaps (0.045"+) helping lower HC emissions (guess) and increase the service interval (guess).

Royce Peterson
December 27th, 2006, 05:54 PM
The Accell coil is intended to be used in conjunction with increased current flow such as would be available if you had 12 volts running through dual points with no ballast resistor. Using this coil with a Pertronix is not going to give any significant increase in ignition power.

Another good way to use the Accell coil would be with a Pertronix triggering device and an MSD6AL ignition amplifier. That wouldgive increased voltage and current on the coil input connection, resulting in increased output to the plugs.

Plug gap depends on the ignition energy available, the mixture quality and the intended usage. If you want the plugs to last 10,000 miles between plug changes then a smaller gap is desirable. You have a carburetor which will give good mixture at some points and not in others. If the car is going to be expected to be reliable and run good at cold start, idling for long periods in traffic, etc then a smaller gap is going to be better.

Any power increase as a result of plug gap will be imaginary in my opinion.




Allright thanks gents for the answers sofar. Still some questions though :confused: (I do believe but also want to understand).

The coil I have is a ACCEL 140001 + ballast resistor. Dizzy is a remanufactored one (autolite?). Spark plugs & cables half year old. Car is driven every working day (but for the coming 3 months as it has gotten colder and they are putting salt on the roads). It has proven very reliable sofar (but for a rear shock coming loose). High-revving is not the intend.

My line of reasoning (sofar) was as follows:
- higher voltage (super coil) means possibility for the spark to jump wider gap
- wider gap means 'longer'' spark
- longer spark means 'more complete' combustion

From what I hear I should lean more towards spark energy? Energy being Volt X Amps, the super coil ups the Voltage but lowers the ''current''. So total energy of spark remains appr the same? So what does the high voltage help with, more reliable spark (because it always jumps)?

Any good book recommendation on this stuff would be appreciated (I already bought ''How to rebuild the small-block Ford'' but it does not dwell [LOL] on sparks & ignition.)

wout67cat
December 28th, 2006, 04:10 AM
tnx Royce,
I'll leave the gap where it is at.

When installing the new dizzy + pertr I had considered adding the MSD. But it seems somewhat over the top for my application. However since it is a hobby I plead the right to change my mind at any time ;-)

The coil was there when I bought the car (however with a too high ballast resistor, making it look like the plugs where failing me).

wouter

Art
December 28th, 2006, 11:14 AM
A pink resistor wire (behind the instrument cluster) decreases the +coil voltage in the "run" circuit.

With the MSD box, the input +coil voltage is not important since the ignition is powered directly from the battery. Coil is wired directly from the MSD box.

The MSD6 is a capacitor bank that greatly increases the voltage to the coil, then the coil steps it up even more. The MSD box gets power directly from the battery via 10ga. wires.

I have the MSD6AL along with a stock Duraspark coil and Duraspark distributor. I gap my plugs .050". I don't believe gap has anything to do with spark plug longevity.

Not all coils are compatable with the MSD6A.

xr7g428
December 28th, 2006, 11:20 AM
This excerpt from Accel refers to the U groove plugs they sell, but it also applys here as it discusses plug gap.


U-Groove began production in 1969 and is the most copied feature on a spark plug today. Most spark plug manufacturers simply widened gap settings to increase the kernel of flame to burn the leaner fuel air mixtures. A negative effect of wider gaps was increased voltage required to fire. The U-Groove allows expansion room to allow a larger flame kernel while reducing voltage required to fire by maintaining the tolerance between center electrode and groundstrap. Reduced fouling potential is a function of the increased number of sharp edges on the ground electrode. A sharp edge collects fewer foul-causing deposits than the flat surface of a conventional electrode. The initial discharge of current from the center electrode is always from the outer circumference because the electrical energy is carried on the outside of the wire that is the center electrode. The U-Groove also "traps" some of the fuel air mixture directly in front of the initial kernel of flame eliciting faster starts and increased throttle response.

dallas121469
January 11th, 2007, 02:11 PM
I accidently gapped my 302 plugs at .050 on a fresh rebuild with higher compression pistons and didnt have any problems. Not to say that in the long run there wouldnt be issues but with all new equipment, including alternator, wires, distributor, voltage regulator etc it ran just fine gapped at .050.

70cat351c
January 11th, 2007, 10:09 PM
OK, fine, since this seems to be such a hot topic I will put in my .02. I have built many supercharged engine combinations and currently help tune cars up to 1400rwhp (with factory computers). I provide tech suport, so I am the guy they call when the tuner can't figure out what is wrong. The one thing that these late model high compresion engines have in common is small plug gaps. When you have that much power in such a small combustion chamber, it becomes more dificult to light the mixture due to higher initial compression pressures. The more dense the air/fuel charge the more voltage you need to jump the gap. Since voltage is hard to come by, the easier thing to do is close the gap. Most supercharged 4.6 aplications that I deal with run a gap of .028-.032. The point I am trying to make here is that these cars maintain factory driveability, emisions and fuel economy. The pressures remain low at idle and while not under boost, so that gap still has to light the same mixture that the factory .056 gap did. The main goal is to make sure that you get a consistant spark that promotes "hatching out" in the cylinder. Once the fuel is lit, the rest is automatic.

If you want my recomendation, convert the car to late model fuel injection with distributorless ignition. Since this is not the goal of most people hear, do what I did previousely; Go to your local junkyard or parts store and find a good duraspark system. Mine cost me less than $100 brand new (- wires) for a 351c. That included the distributor, cap, rotor, adaptor (for the large cap), and ignition module. Wire it up, hide it in the fender if you don't want it to be seen, and go. Follow the plug gap recomendations of a similar aplication that had the same plugs and compression.

I did not recomend the MSD, and here is why; A lot of people I know who race with MSD cary a spare box with them. 'Nuf said.

James