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Old 04-30-2008, 01:10 PM   #41
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Originally Posted by The_Pipefather View Post
And, as to why this is needed, you discharge the coils half as often compared to the present wasted spark setup so:

1) Your coils would last twice as longer (theoretically speaking).

2) You would have a lot more spark energy available and therefore, all of the spark energy available due to capacitive discharge can be exploited. In essence this would mean you can open up that spark plug gap even more.
1) I kinda doubt that.
2) No, it's not gonna be a lot more. The coils charge and discharge. I don't have my books and formulas, but doubling charge time doesn't double spark. If the coil gets 99.5% charged before you spark, and then you give it twice as much time to charge, your working on getting that last 0.5%. Granted as RPM increase the time the coils have to charge decreases, but that doesn't mean spark power drops linearly with time.

But get er dun. I'm MS II so If I ever do COPs I wanna do them sequential, since I already have a crank wheel and plenty of outputs.
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Old 04-30-2008, 01:12 PM   #42
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I'll buy the increased longevity concept. Fewer firings, less heat. Maybe.

Not sure about the "Spark Energy" concept, though. That is almost entirely a function of dwell time, and we're not running into a dwell limitation. For an engine turning 8,000 RPM, running wasted spark, there are 133 ignition events per coil per second, or 7.5 milliseconds between each ignition event. With the stock coils, we typically run ~5ms dwell, and with the COPs we run even less (somebody help me out here- 3ms? 3.5? Something like that)

Point is that once the primary winding is fully saturated, increasing the dwell doesn't get you anything except a damaged primary winding. And with wasted-spark, there is more than adequate time to reach full saturation.

Ok- to be purely academic, if the coil fires half as often, then the windings will run *slightly* cooler, the DC resistance on the primary will be *slightly* lower, and therefore the saturated charge current will be *slightly* higher. But you'd need a pretty accurate scope to notice.
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Old 04-30-2008, 01:16 PM   #43
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One might make the argument that extra power could come from less voltage drop, since the dwell time is fixed off batt power not off voltage at the coils themselves.
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Old 04-30-2008, 01:18 PM   #44
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One might make the argument that extra power could come from less voltage drop, since the dwell time is fixed off batt power not off voltage at the coils themselves.
This is true. The supply wire running to the coils is kinda puny, hence the "Cap mod" that folks are talking about now. Charging one coil vs. two means less drop across the V+ supply wire. Increasing the voltage available at the coil would raise the saturation point.
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Old 04-30-2008, 01:22 PM   #45
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OEMs run sequential COP because it extends the lean misfire limit. Guess we dont really need to run that lean, except off-boost.

Anyway, I'm going to compare both and see if there's a difference or not. Sometimes things don't always follow theory.



Couple of quick questions for you guys:

1) If the 94+ CAS is magnetic (VR), then how can it give the same signal as the 90-93 optical (Hall) CAS?

2) The COPs that you guys run now, is it inductive coil or CDI?

Last edited by The_Pipefather; 04-30-2008 at 01:40 PM.
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Old 04-30-2008, 01:57 PM   #46
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1) If the 94+ CAS is magnetic (VR), then how can it give the same signal as the 90-93 optical (Hall) CAS?
First, Hall and Optical are not the same thing. From a pure physics standpoint, Hall has more in common with VR than it does with optical. Though the more I think about it, I believe (purely from looking at the rotor) that the late-NA sensor may in fact be VR rather than Hall as is commonly thought.

The signals are the same between the two CASs because they both contain an active circuit which provides a squarewave output via an open-collector driver (that's why they require an external +12 supply to operate). By contrast, most VR sensors that we see in Ford EDIS applications or DIY crank triggers do not contain an active driver- they emit a raw AC waveform and thus require an external circuit to derive a TTL-compatible squarewave from them.
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Old 10-04-2008, 12:59 AM   #47
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Ok I went to the yard and picked up a CAS. I have some interesting findings for you guys:

1) A Ford Festiva has the exact same optical CAS as the 90-93 miata, except that there is only one inner slot. It looks the same as the pic Joe posted, except that the inner lower slot isn't there. This would give the required 4 + 1 pulse.
Anyone done this? Do you have to fit the Festiva disc into the 1.6 CAS?
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Old 10-04-2008, 01:46 AM   #48
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No, I believe The Pipefathers observation was that the Ford CAS is a direct fit, both electrically and mechanically, into the Miata. Thus, no need to dismantle anything, just remove the Miata 4-2 CAS and install the Ford 4-1 unit.
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Old 10-05-2008, 11:30 PM   #49
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No, I believe The Pipefathers observation was that the Ford CAS is a direct fit, both electrically and mechanically, into the Miata. Thus, no need to dismantle anything, just remove the Miata 4-2 CAS and install the Ford 4-1 unit.
But no Festiva came with a plain CAS. They came with distributors with an optical sensor in place of points.
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Old 10-05-2008, 11:39 PM   #50
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Two optical sensors, as far as I'm aware. Which, when you discard the cap and rotor, is pretty much equivalent to a Miata CAS, in a 4/1 configuration.
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Old 10-06-2008, 12:22 AM   #51
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totally off-topic, but modernbeat, are you the same one who had the black B-mod Locost?
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Old 11-18-2009, 04:04 PM   #52
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I know I'm digging this up from the past but does anyone know if there need to be any modifications done internally to the megasquirt to enable sequential?
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Old 11-18-2009, 04:11 PM   #53
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for sequential spark, you need to free up some outputs and run some additional wires both internally as externally.
For sequential fuel you can install Jean Bélanger's board without having to give up outputs. Again, modifications inside and additional wiring on your '91.
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Old 11-18-2009, 04:24 PM   #54
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Originally Posted by swerv_on View Post
I know I'm digging this up from the past but does anyone know if there need to be any modifications done internally to the megasquirt to enable sequential?
Once you've dealt with the matter of having one cam pulse per cam revolution, all you need to do is enable SparkC and SparkD as outputs in the software, and the build a pair of spark output drivers to mirror what you've done on the primary (D14/D16) drivers.
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Old 11-18-2009, 05:35 PM   #55
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Once you've dealt with the matter of having one cam pulse per cam revolution, all you need to do is enable SparkC and SparkD as outputs in the software, and the build a pair of spark output drivers to mirror what you've done on the primary (D14/D16) drivers.
36-1.
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Old 11-18-2009, 07:33 PM   #56
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A 36-1 wheel, by itself, is not sufficient. You must have a cam pulse in order to run full sequential, and it must be exactly one pulse per cam revolution.
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Old 11-19-2009, 01:49 AM   #57
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Once you've dealt with the matter of having one cam pulse per cam revolution, all you need to do is enable SparkC and SparkD as outputs in the software, and the build a pair of spark output drivers to mirror what you've done on the primary (D14/D16) drivers.
Already have a Festiva CAS on the way so that much is covered. I know next to nothing about designing circuits so bare with me here... So I basically need to make a second set of spark out put drivers in the proto area of the board. What areas of the board do I need to jump from and to, to make that work?

Also I remember when building the harness that your supposed to pair pin 32 and 33 together as well as 34 and 35 for the spark out. In theory couldn't you just keep them separate and run the triggers individually off each pin? Again I know nothing about circuit design.
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Old 11-19-2009, 01:11 PM   #58
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So I basically need to make a second set of spark out put drivers in the proto area of the board. What areas of the board do I need to jump from and to, to make that work?
SparkC is taken from D15 (top of R27) and is thus identical to your existing SparkA and SparkB. It can be build on the back of the board just like the others.

Spark D is a little weirder. You remove R1, and wire to the bottom pad of where it came from. Then build (in the proto area) and circuit which replicates the LED driver circuis (you can omit the LED itself) and connect R1 through a 1k resistor to the base of the new transistor.







Quote:
Also I remember when building the harness that your supposed to pair pin 32 and 33 together as well as 34 and 35 for the spark out.
Those pins are for the fuel injectors, not the ignition. And they're paralleled just to increase their current-handling ability. For spark, just pick any four pins that aren't otherwise in use.
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Old 11-19-2009, 02:11 PM   #59
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Thanks for the help guys, can't wait for this weekend to make this happen.
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Old 11-19-2009, 03:01 PM   #60
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