Yup, replaced the coil with a hi-po one, but I believe that one of the benefits of the higher power is control over my drinking - - - NO, strike that....... One of the benefits is/was supposed to be a better spark, but if I leave the plugs gapped at stock (0.25), the bigger spark is going to be not so much bigger. So, what do I gap the plugs at?? And, in addition, how can I tell if the spark is being blown out because of too much gap?? A simple misfire?? Thanks, Cosmo P.S. Car is 2CV, coil is Dyna for Jap fours (twinned output).
I would gap them at the stock spec, but I'm no horsepower genius. I think the benefit of a better coil is a hotter spark, not a bigger one.
Open up gap .005 at a time and see how it runs.Make sure all ignition parts ,cap ,rotor, condenser points, wires ,dwell and plugs are in good shape.Wider gap will idle smoother and help driveability.
In theory the bigger the spark gap the better the flame, and the fewer misfires. In practice however, it is limited by the "weakest link". When GM first came out with it's powerful HEI ignition, they recommended a .060 plug gap. That worked very well AS LONG AS everything was in great shape. Soon they found out that a large gap also invited the spark to go elsewhere if there were any weak spots. If the plug gap eroded too big (high resistance), or the rotor got some normal dust on it, or an aftermarket rotor was thin in spots, the spark would jump thru the rotor and start welding the advance weights. If a plug wire would deteriorate a bit, even if it was still way above the older ignition wire standards quality-wise, the spark could still find an easier path, maybe from a coil mounting screw to the nearest plug wire terminal, and sometimes arc internally in the coil itself. After a few years, it became a racer standard practice to run gaps of about .045 to reduce the tendency for the spark to find an easier path when under pressure. (thats when using heavy duty racing ignition parts) My point is now that your ignition may be capable of higher power, the "other" weak spots in your system may still be the limiting factor as to how much pressure (high resistance big-gap) it can stand before the spark finds an easier route anyway. If you run the gap bigger you might find out that the stock-type plug wires could be the next weak spot to allow cross firing, or cap-terminals too close, or the stock type coils might prone to internal sparking if resistance is too high, or or or My point is that if some pieces in the rest of your igniton are still stock-type, built for a lower power system, opening up the plug gaps much at all could be moving a misfire around to different parts of the system until you eventually beef up everything. Keeping a smaller gap may be a safe thing to do if you aren't sure just how well the other parts can keep the higher power going where it should. You could try using a moderately larger gap, and you may likely see improvements, but how could you tell if you reach the point where a 1% misfire rate becomes a 3% misfire rate, and you need to close the gap a tiny bit? Experiment, and experiment, or play it safe. That depends on how you aproach your hobby. If you want to spend the time, you could "play it safe" for a while to see what you have. Then try .030 then .035 gaps and see if things improve or do not improve, but I myself would do that only after good quality plug wires, a good coil I could trust, quality cap and rotor, good insulators on the wire looms if I used any, etc etc. If you don't consider experimentation, close monitoring during the experiment, etc to be a fun pastime, don't open the gap by very much. One Studebaker friend of mine liked to travel in his streamlined 55 Coupe with a 259 engine. 3 spd overdrive. I made him an HEI ignition, and some big-valve heads for it. He liked to experiment. He used a whopping .080 plug gap (I don't recommend that), inflated the 205-15 tires to 42-45 lbs, ran 3.38 gears with the Overdrive, and claimed 32 MPG (3700 lb car) on long trips using a Dodge 2bbl carb. The car would still lay rubber in the first two gears.
The way this was explained to me is, The high voltage coil builds current until it can overcome the resistance of the gap and jump to ground, making the spark. If you leave your gap the same the spark will jump at the same voltage it always did and you will gain nothing in voltage. Or the spark is not hotter. So you need to increase the gap to take advantage of the high dollr coil. That's what I was told. Guy could have been full of it, but it sounds good.
I agree. The voltage MUST build up to a certain power level before it can jump. Often, it's the gap between rotor and cap terminal, but it could be at the plug gap if the plug gap is large. Generally speaking, the bigger the plug gap the bigger the results, but it is hard to guess when it's time to stop enlarging it or when you go too far. I forgot to mention- my friend with the 32 MPG V8 Stude used a spark plug side-gapping trick we used on our race car. He said his mileage and power improved. 2 mpg increase. On the race car, it was worth about a tenth of a second at the drags, but that is hard to say for sure exactly how much. I used to take some pliers , diagonal-cutters, and snip back the ground electrode so just over half its length was left. Then I would carefully bend the ground electrode to get about an .050 gap on the race car, while my friend used .080 (NOT recommended) on his travelling car. The idea was to give the spark a sharp jagged edge (the spark jumps easier from a sharp edge) and to expose the spark instead of having a hidden spark that most spark plugs have. I forgot where I first read about side-gapping. Probably Popular Hot Rodding back in the 1970's. (are they still around?) It works, and it costs nothing. People who have tried it can definitely tell a difference.
So.....an old tuners trick is to "phase" the distributor rotor. This is a method whereby you place the rotor at such a point that the advance system begins jumping the spark to the cap at idle - sweeps past the stud in the cap - and ends up at a planned point at full advance. MSD actually sells an adjustable rotor......or hot rodders find their own way... Usually done by cutting a hole in a sacrificial cap and watching through the window with a timing light in dark or semi-dark DON"T GRAB THE FAN, BELTS, OR A HEADER PIPE. When its where you like it - on my old drag race car we made the closest gap occur at full advance - then you can judge whats best for the plug. If you are running an induction ignition system with a low resistance (HOT) coil and lots of "dwell" (electronic or points either one) try .045 and go from there.
If I read this correctly...this is a direct double coil setup with no cap or rotor? If so, with new coil and new wires routed well away from ground you would not have all the secondary weak links of normal elderly distributors.
Yup. One set of points, wasted spark system. Opposed twin, think BMW M/C. I want to thank those who answered. I learned much that I didn't know about ignitions. I may try the cut-back ground, as NGK B8HS plugs are cheap, and I only use two of 'em. Cosmo
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