The '49-'59 "Parts & Accessories" catalog apparently lists the same coil for all '57 models, including blown/dual point equipped. If increased dwell time/heat resulted in more coil failures, then the two year interval (and limited SC production) didn't warrant FoMoCo recommending an upgraded/superseded replacement part. WAS an OEM coil really adequate I wonder, or did it just take longer for them to fail? Did a HD coil ever become the accepted standard for a dual point conversion, or Mallory (etc.) type distributor upgrade?

6 VOLTS/POS. GRD. NW INDIANA

It appears to me that any nicely set-up and tuned dual point will make plenty of spark power. Its the limitation of how many amps and volts the contacts will handle (before burning) that sets the upper limit. Reliability is a drawback to the old school dual-point - and maybe not even that for a "Saturday Night Special" that only builds a fire every once in a while. It does have a rev limit though - sooner or later even the dual points will float.

The homebuilt electronic ignition in my bird uses a Ford Duraspark II trigger in the dizzy - and for everyday use, a "Standard" or "Wells" cheapo control box to provide a switching transistor and set the dwell (25°). The coil is an MSD (.88 OHMs) and I run an MSD ballast resistor (also .88 OHMs) for about 1.8 total. I've also run it with a Ford TFI epoxy coil (1.2 OHMs) and no ballast resistor - which worked OK and made nice fat blue sparks, but I don't have an idea for how long the cheapy control boxes will take the heat in the switching transistor. For my purposes, I'd rather error on the side of inexpensive and reliable power - so this is definitely not a maximum performance arrangement.

I have an Accel HEI (4 pin) variable dwell style controller rigged up to plug into the Duraspark II trigger and it will make very acceptable sparks with either of the two coils (with no ballast resistor) - but I haven't checked to see just what range of dwell alteration is available. 

 
 Steve Metzger       Tucson, Arizona

I believe the practical limit to the plug gap issue is ......whatever works. If the gap is too big and your energy source isn't big enough  - you will probably get enough misfires to want to try something else. If your set-up will tolerate .045 - and no misfires - run it. If it won't - try .040 - and so on.Thats what tuners do.....

It takes about 10,000-12,000 volts to make the plugs fire in an engine - the high dielectric ratings you see are not specifically what the coil delivers every time - its just how high the voltage can safely go before it tries to jump between windings. Dielectric strength isn't a big issue with most modern materials - heat is.

Maximum "dwell" on an old style distributor (with points) is 45° - at which point the cam is round and the points don't open - and it won't work. Comparing the real dwell setting (say 26°) with 45° will give you the duty cycle of the coil - 26/45 = 58%. This number is basically fixed until the points "float". The typical old stocker set-up is rigged with ballast resistance - and internal coil resistance - such that at 58% duty cycle the life of the oil filled coil is virtually infinite. I've got an old Ford coil on my bench that ran 50 years and 100,000 miles - nice design work for reliability in anyone's book. Not high performance though.

So you try a dual point that using combined the "open/close" point overlap makes the dwell 34° - and now the duty cycle is 76%. Available spark energy is improved by 30%. Does the coil cook? Some did (heat went up by 30%) - and it became popular to use coils that were "epoxy filled" to handle the heating - or maybe one of those big old Mallory or Accel coils that would just flat absorb more heat and take it. Could they handle more plug gap? Probably - see paragraph number one.

 
 Steve Metzger       Tucson, Arizona

I have used Peritronix in my 2 mustangs with good results.  I have seen reference to "converting to a duraspark II" in threads.  Is that a better option and if so whats involved?

Anyone know offhand how the increased dwell time possible with dual point conversion might relate to plug gap/coil selection?

6 VOLTS/POS. GRD. NW INDIANA

All of the electronic ignitions that operate as an Inductor system (not as a Capacitive Discharge unit) have some common operating items:

(1) A power transistor that is used to ground the negative side of the coil (just like the points did). Just like the points, these transistors have limitations as to how many amps and volts they can handle and for how long. When a set of instructions tells you what the minimum allowable ohms of resistance may be in the coil - they are indirectly telling you what the transistor can handle. Volts equals Amps times OHMs - if you know the Volts and the OHMs - you can figure the Amps. Volts times Amps equals Watts - the power rating for the transistor (there is a missing time factor here). The real capacity of the unit is something in WATT milliseconds.

(2) An integrated circuit chip that controls timing - it sets the "dwell" time to close the power transistor and charge the coil. Some are "smart" - alter the dwell with rpm to try and extend the coil charge time for more performance (and reduce it at idle to save the transistor from heating)......and some just use a fixed amount that suits low/medium rpm and that's it. You can test your unit by simply hooking up a "dwell tachometer" to the negative post of your coil and getting an idea of the dwell your system runs at. If the Accel sytem is variable that would be a good thing -assuming the dwell increases with RPM. I've got a good idea the basic Pertronix Ignitor doesn't.

(3) A trigger to monitor engine crankshaft revolutions via some sort of "no wear" magnetic device mounted in the distributor. Most of these are pretty trouble free. The Ford Duraspark II unit is notably bulletproof. The MSD distributors use the Ford trigger system.

There is really only one performance related thing you can personally control when you buy one of these systems - how many watts can you feed the coil. If the instructions say 1.5 OHMs total resistance (like the Pertronix Ignitor) - make sure that's what you've got, no more no less. Do away with the ballast resistor and buy a coil with 1.5 OHMs resistance. The GM HEI timing system - and I think your Accel unit is using the same dwell time controller - doesn't care too much about coil OHMs - it simply adjusts the dwell ("on time") to control transistor heating. If you have too much resistance in an HEI type system you will lose performance because you can't leave the coil "on" long enough to get good performance as the rev's go up. Choose a lower resistance coil for that sort of application.

 
 Steve Metzger       Tucson, Arizona

Now my question is:I installed an accel ignition kit on my 56 after replacing the distributor with the later one.Is it comparable to the pertronix in terms of performance?I have not yet replaced the coil with a high voltage unit.Haven't heard any feedback on the unit I installed as far as problems etc.Thanks Mark

  

And Sasebo and Olongapo?

You gotta have the right tools and know how to use 'em.

TC - Austin, Texas

What about Taiwan and Okinawa?

55Birdman  Hickory NC

Sounds like we all have the same idea, I too have the Petronix with the Flamethrower coil. .045" on the plugs too. I have a Petronix in every car I have that came with points, first one was 12 years ago, and they all run great.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias