It has one other fun feature,  occasionally it will set off the alarm of an adjacent car when you start yours.  It seems to affect 'vettes most and always makes me laugh!!

  The main feature of an MSD or a Crane is that at lower RPM's, below 3000 or so. it fires the plug 6-8 times per cycle. This reduces misfires and helps low end torque. Do you have to have it, no. But if you put one on, you won't ever want to take it off. Again, look at a 6a or the Crane unit, they are less expensive than the more common 6AL, which has vibration proofing for race cars. 

Frank do you have a part # for the coil?

Use a coil spec'd for use with a capacitive discharge system - in this application they serve a slightly different purpose than we are used to with the inductive sparkerizers - the CD uses them as a step up transformer - like a 100:1 step up - so get one made for the purpose.   

          Steve's trying to tell you that you ought to use the MSD coil, and I don't have a number. Summit will. The stock coil will work, but a Capacitive Discharge specific unit will work significantly better, and longer. Also, very importantly use new GOOD 7 or 8 mm wires. You'll need them. If you don't believe that, start it at night with the hood open, turn the lights off and watch the fire works from the old wires. USE RESISTOR WIRES. Gap the plugs at least to .045 or .050

Frank's right about the wires.  Once I was trying to sort out an electrical problem, and I thought maybe the rotor had shorted to ground.  I took off the cap and held the coil wire about 1/2" from the rotor button and cranked the engine.  The spark jumped from the wire to the rotor and from the tip of the rotor to the distributor housing around and around, 8 sparks per revolution.  Takes a good wire to contain that.

I once worked for a guy that raced a big block scrub, and he cut the ground electrode off the plugs so the spark would jump directly to the piston.  I don't think I would do that, but he claimed better combustion.  I'm sure he read that somewhere, he's not mechanic enough to think of that.

John in Selma, IN

Probalby.  Electricity wants to take the path of least resistance, so as long as the least resistant path is the spark plug gap, that's where it will go.  I must be like electricity.  I like to follow the path of least resistance also.

John

Earl.  Not to contradict everyone and their fascination for the larger plug gaps but you can get away with not regapping until the next time you have the spark plugs removed either for service or replacement.  The larger gaps work to an advantage on fuel injected vehicles but I find very few instances on carbureted cars where it is of an added benefit and in fact puts an increased load on the ignition circuit creating some premature failures depending upon the particular pointless ignition being used.  The stronger spark just allows a wider gap without the misfiring associated with the older points systems and its associated weaker spark.  I know I’ll probably get some rebuttals on this but I’ve quite a bit of dyno data to back me up as well as testing in the drag cars.

       I think MSD recommends a wider Gap. This all started with the smoggers back in the 70's when they found better ignition with a hotter, longer spark, mostly due to the leaner than optimum mixtures they needed to run before cats were used.   

        See, this modern electronic stuff is amazing ain't it!

       More on Ted's comments, spent some time thinking about what he said today. Some of this is guesswork on my part, based on knowing how thorough Ted is and how "picky" for lack of a better word, he is. I would guess that his plugs are usually new, his jetting is on and the motors he runs are usually sealed up and not burning oil. Based on that, he might not see much if any difference with a .045 gap versus a .035. I would expect the major improvement to be in less optimum cases where there's some oil burning and a less than perfect mixture. I did notice some improvement in the blown car, with old wires, by closing my gaps to 42 from 45. On my Pontiacs, the MPH would pick up by going wider. No blower, 9 to 1 compression and a Quadrajet Carb. My Windsor doesn't seem to care, but it idles better with the bigger gaps. 

charliemccraney (10/29/2008)

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depending upon the particular pointless ignition being used.

If I spend all that money on an ignition it better not be pointless.

Charlie.  This proves you do have a sense of humor.  For you, I’ll change ‘pointless’ to ‘breakerless’.

Frank.  Thanks for the kind words but spark plug life in the roadster's Y is like my other race cars in that the plugs want to last forever.  You gotta thank modern ‘breakerless’ ignitions for that.  Looking back through the records for that particular engine, the plugs were changed out at the Birdsapallooza event in May of 2005 and have been doing their job since without a hiccup.  But you’re right on the jetting as I’m always adjusting on that.  Regarding spark plug gaps, I believe Steve Metzger pretty well covered it in a post he wrote yesterday in a separate but similar thread.

http://www.y-blocksforever.com/forums/Topic17921-3-2.aspx

But this is a good topic as it gets the mental juices to flowing so I’ll add some more thoughts.  Leaner mixtures typically like a wider gap and fuel injection systems in general puts an emphasis on ‘lean’ during cruise situations.  In a lean situation, a wider gap give the spark more time to ‘find’ and ignite the mixture.  On a sidenote, the BG Demon line of carburetors will typically like both a wider plug gap and increased advance for the initial ignition timing settings more so than the Holley carbs simply because of the leaner idle and cruise mixtures they exhibit.  I do recognize that the requirements between idle/cruise and full throttle are also different in regards to spark plug gapping.

On the flip side, higher combustion pressures increases the need for a stronger spark while maintaining a given gap.  Because the ignition system is either maxed out already or not being upgraded, the spark plug gap is easily reduced to fit any increases in demands that are being placed upon the ignition system.  I simply run across too many instances in a performance situation where an engine is misfiring at the top end of its power band and the first thing I do is have the customer reduce the plug gap which in a majority of the cases is the fix.  I get chastized quite a bit for sending engines out of the shop with a smaller than recommended plug gap but it’s one area of troubleshooting that does not have to be revisited if an issue crops up.

I recently reduced the gap in my roadster engine from 0.035” (Columbus setting) to 0.025” and was rewarded with a personal best for the Y engine that resides between the rails.  These are the same plugs that I’ve been running since 2005 but simply regapped.  I’ll accept that the et reduction wasn’t all plug gap related as the air was good but still feel confident that plug gapping was still a contributor.  This is something I picked up from recent dyno testing where spark plug gapping was the emphasis and simply put those learnings to use on the car.  Again, this is full throttle testing which will differ from cruise situations.

Here’s an et slip from a couple of weeks ago with the 0.025” plug gaps.  As an FYI, the slowest pass for the day was a 9.67 et.  I’m car # 411E and in the right lane.

The energy is volts times amps - and whatever it takes in volts to make the jump, reduces the amps (and vice versa). It supposedly takes about 10,000 volts to fire a pressurized engine cylinder - don't know what gap is assumed there - but if the gap is enlarged and the volts raise - the amps must fall.

When we are welding - we adjust amps to get the heat right - my guess is, that when we fool with the plug gaps, we are adjusting the balance between amps and volts to suit the compression/mixture - and get the heat right.

          Humour is when I say it, sarcasm is when somebody else thinks of it first!.

 Ted, I am running an MSD blaster, but the blower makes my experiences in this car not directly transferable. I have not had any top end misfire issues, that I'm aware of, with the Duraspark, Flamethrower, 6AL combo. But, if I can quit breaking parts long enough to get a couple of runs in, I will try closing the gaps up to see if there's any noticeable difference.