Msd Blaster 2 Coils
05-08-2004, 01:47 PM
#41
Senior Member
Join Date: Nov 2003
Posts: 480
Okay, so I just checked an MSD 6A on the scope - it thinks it's an
8 cylinder (ie multisparks to 6000 RPM on a 4 cyl, multisparking
continues for 40 degrees, not 20). Of course that second spark at
6000 is 36 degrees late, so it's of questionable use. I don't know
if this will change on a 6AL if you snip the wires - can't seem to
find my 6AL. There is probably a 4 cyl version available that would
spark as advertised and thus use less power and beat up the plugs,
cap,rotor less.
There are various common misuderstandings abound regarding how the 6A
works. The 20 degrees they refer to is how long the box is allowed
to spark. There is a circuit that times the incoming spark pulses,
assumes 90 degrees (8 cyl, remember) between them, and makes a 20
degree pulse based on this time (it's actually a very simple circuit).
During this pulse, the box will spark every millisecond. At ~3000 RPM,
1 millisecond is about 20 degrees, so there is no time to multispark
anymore so it only fires once. There isn't a "mode change", and the
spark at this point is not 20 degrees in duration. How long it is in
microseconds depends on the coil parameters (and if you rev it up
enough, you might just get 20 degrees, as this duration doesn't
change with RPM).
The analog MSD series probably has the fastest recharge of any CDI
you will find (but 1 ms restrike is fairly typical). It contains
what amounts to a Kettering ignition - for a short time it applies
lots of current to a transformer, then cuts it off. The secondary
flyback then charges the capacitor in one fell swoop - it is now ready
to fire. With this in mind, those thick power leads are crucial.
Probably most of the people who claims MSD's don't work have been
negligent in this area. Also, that big capacitor they sell as a
noise suppressor may be helpful performancewise. You can save $$$
by buying a similar capacitor from a surplus dealer.
Check out patent # 4,131,100 on www.uspto.gov for lots of info.
Finally, I will point out that power comsumption of an MSD isn't
that much on average. It peaks very high (over 30 amps), but that's
for a really short time. I believe it is probably on par with a
factory ignition (very wasteful).
Is your Chrylser box one with that funny 5 pin connector? I kind
of thought that type used a ballast resistor. IMHO, the ignition
should be able to current limit without resorting to a resistor,
which will hinder high RPM performance.
Also I will point out that most factory OEM E-core style coils are
quite good. You kind of need an LCR meter to evaluate them though.
The coil on my Accord is electrically very good but I don't think
it would work at high RPM in a Kettering ignition due to high
inductance.
8 cylinder (ie multisparks to 6000 RPM on a 4 cyl, multisparking
continues for 40 degrees, not 20). Of course that second spark at
6000 is 36 degrees late, so it's of questionable use. I don't know
if this will change on a 6AL if you snip the wires - can't seem to
find my 6AL. There is probably a 4 cyl version available that would
spark as advertised and thus use less power and beat up the plugs,
cap,rotor less.
There are various common misuderstandings abound regarding how the 6A
works. The 20 degrees they refer to is how long the box is allowed
to spark. There is a circuit that times the incoming spark pulses,
assumes 90 degrees (8 cyl, remember) between them, and makes a 20
degree pulse based on this time (it's actually a very simple circuit).
During this pulse, the box will spark every millisecond. At ~3000 RPM,
1 millisecond is about 20 degrees, so there is no time to multispark
anymore so it only fires once. There isn't a "mode change", and the
spark at this point is not 20 degrees in duration. How long it is in
microseconds depends on the coil parameters (and if you rev it up
enough, you might just get 20 degrees, as this duration doesn't
change with RPM).
The analog MSD series probably has the fastest recharge of any CDI
you will find (but 1 ms restrike is fairly typical). It contains
what amounts to a Kettering ignition - for a short time it applies
lots of current to a transformer, then cuts it off. The secondary
flyback then charges the capacitor in one fell swoop - it is now ready
to fire. With this in mind, those thick power leads are crucial.
Probably most of the people who claims MSD's don't work have been
negligent in this area. Also, that big capacitor they sell as a
noise suppressor may be helpful performancewise. You can save $$$
by buying a similar capacitor from a surplus dealer.
Check out patent # 4,131,100 on www.uspto.gov for lots of info.
Finally, I will point out that power comsumption of an MSD isn't
that much on average. It peaks very high (over 30 amps), but that's
for a really short time. I believe it is probably on par with a
factory ignition (very wasteful).
Is your Chrylser box one with that funny 5 pin connector? I kind
of thought that type used a ballast resistor. IMHO, the ignition
should be able to current limit without resorting to a resistor,
which will hinder high RPM performance.
Also I will point out that most factory OEM E-core style coils are
quite good. You kind of need an LCR meter to evaluate them though.
The coil on my Accord is electrically very good but I don't think
it would work at high RPM in a Kettering ignition due to high
inductance.
05-08-2004, 06:46 PM
#42
Senior Member
Join Date: Nov 2001
Posts: 2,284
Wow, you've answered some questions I've had for a long time about the MSD. Thanks.
The Chrysler box does have the five pin connector. I may not be able to use it because my dad's van uses that type of ignitor. He might want it for a spare. We'll see.
I think what I'll do is use the trailing ignitor on the trailing coil. It may not fire reliably while cranking, but it should be fine at idle and above. I'll see if it burns out at high RPM (8-9K). I'll also wire in a switch to turn it off while doing burnouts so I don't accidentally over rev like SPRT did to his 12A with an MSD 6AL on leading. It was rev limited to something like 8400, but as the rev limiter was kicking in, the trailing ignition was still enough to over rev the engine and the apex seals broke.
The Chrysler box does have the five pin connector. I may not be able to use it because my dad's van uses that type of ignitor. He might want it for a spare. We'll see.
I think what I'll do is use the trailing ignitor on the trailing coil. It may not fire reliably while cranking, but it should be fine at idle and above. I'll see if it burns out at high RPM (8-9K). I'll also wire in a switch to turn it off while doing burnouts so I don't accidentally over rev like SPRT did to his 12A with an MSD 6AL on leading. It was rev limited to something like 8400, but as the rev limiter was kicking in, the trailing ignition was still enough to over rev the engine and the apex seals broke.
05-09-2004, 10:41 AM
#43
Senior Member
Join Date: Nov 2003
Posts: 480
You might want to add a resistor in the trigger lead to take some of the
strain off the ignitor. Start with maybe 10K and work down until you get
decent low RPM triggering.
Here's a link to some info on CDI:
http://www.beyond-designs.com/pspice_CD.htm
There's a link on that page to another about inductive.
strain off the ignitor. Start with maybe 10K and work down until you get
decent low RPM triggering.
Here's a link to some info on CDI:
http://www.beyond-designs.com/pspice_CD.htm
There's a link on that page to another about inductive.
05-09-2004, 01:39 PM
#46
Senior Member
Join Date: Nov 2001
Posts: 2,284
Oh, ok. Stuff like this makes me wish FC stuff was 2nd nature to me like FB stuff is. Oh well, I guess it just takes time. Besides, the way you explained it above makes more sense. The thought of a capacitor popped in my mind as I was typing my post above. Man, it's been a while since I was really into electronics, as you can see.
05-17-2004, 08:25 PM
#47
Member
Join Date: Mar 2003
Posts: 40
Originally Posted by 83turbo' date='May 3 2004, 03:37 PM
The red wire (trigger) is soldered on to a terminal labeled "?GT"
(can't read the 1st character because of the wire). Tan goes to
"B??", and black goes to "C".
The resistor can be located on the tan or black wires - I've
seen both configurations.
Note that this ignitor doesn't do active dwell control - it just
turns on the coil when the red wire is + (although after a couple
of seconds it will shut off). So, if the trigger pulse is too short
it really won't work right.
Also the lead coil has the lowest primary resistance of any inductive
coil I have ever tested. Why the trail is different I don't know.
Also, the trail coil has a "secondary gap" inside it - if you
try to measure secondary resistance, it appears open.
(can't read the 1st character because of the wire). Tan goes to
"B??", and black goes to "C".
The resistor can be located on the tan or black wires - I've
seen both configurations.
Note that this ignitor doesn't do active dwell control - it just
turns on the coil when the red wire is + (although after a couple
of seconds it will shut off). So, if the trigger pulse is too short
it really won't work right.
Also the lead coil has the lowest primary resistance of any inductive
coil I have ever tested. Why the trail is different I don't know.
Also, the trail coil has a "secondary gap" inside it - if you
try to measure secondary resistance, it appears open.
http://www.teamfc3s.org/info/articles/demystifying.html
it appears the coil starts charging before the 5v IgT signal arrives from the ecu. Can anyone shed any light on this?
If the leading coil ignitor does provide dwell control, then adapting it to 1st gen ignition duties should be much easier, as the trailing edge of the IgT signal is all that's needed to fire the coil.
05-18-2004, 11:46 AM
#48
Senior Member
Join Date: Nov 2003
Posts: 480
The lead is basically a "dumb ignitor". It does the following:
1-turn on the coil when signaled by the ECU
2-limit max current
3-if the ECU fails to turn off the signal within (some fraction of a second), turn off the coil.
In the scope trace shown on that page, it does look like dwell begins before IgT rises. However, my own observations on the scope do not match this. I'm not sure what's going on here - maybe the design changed at some point - although I have lead ignitors from different years, and none differ in that respect.
When I tried firing the lead ignitor with a mag pickup (not recommended practice), The spark was quite weak looking, and on the scope I could see alot of "scatter" in the dwell period. Peak current was never reached. With the trail, dwell period was constant and always showed the correct peak current.
The dwell period the trail ignitor uses seems to be chosen for minimum power consumption - it's just a ramp with no plateau before firing. The problem here is that if you accelerate rapidly, it "waits too long" before re-applying coil power after the previous firing, and doesn't peak. I'm not sure how much you can lose in real life. On the bench I could make those peaks cut way down.
I would think your best bet for adapting the lead ignitor to a first gen is to use a PNP transistor fired by the J109 ignitor output.
1-turn on the coil when signaled by the ECU
2-limit max current
3-if the ECU fails to turn off the signal within (some fraction of a second), turn off the coil.
In the scope trace shown on that page, it does look like dwell begins before IgT rises. However, my own observations on the scope do not match this. I'm not sure what's going on here - maybe the design changed at some point - although I have lead ignitors from different years, and none differ in that respect.
When I tried firing the lead ignitor with a mag pickup (not recommended practice), The spark was quite weak looking, and on the scope I could see alot of "scatter" in the dwell period. Peak current was never reached. With the trail, dwell period was constant and always showed the correct peak current.
The dwell period the trail ignitor uses seems to be chosen for minimum power consumption - it's just a ramp with no plateau before firing. The problem here is that if you accelerate rapidly, it "waits too long" before re-applying coil power after the previous firing, and doesn't peak. I'm not sure how much you can lose in real life. On the bench I could make those peaks cut way down.
I would think your best bet for adapting the lead ignitor to a first gen is to use a PNP transistor fired by the J109 ignitor output.
05-20-2004, 10:21 PM
#49
Member
Join Date: Mar 2003
Posts: 40
Glad to hear your knowledge comes from actual testing. Kudos to you for putting in the effort. I just got a scope the other day to do the same type of testing, as I've got 3 or 4 FC leading coils I can put on test. Strange, though, in that the answer I got on the big forum was that the FC ignitors are all 'smart', ie with active dwell control.
In my experimental setup, the ecu can provide an accurate falling edge signal to trigger the spark event, but there is no easy way to also provide dwell control via the trigger signal given the limited timer resources. Looks like I'll have to use one of those 4-wire GM ignitors for dwell purposes. Thanks again for the info. Very informative thread.
In my experimental setup, the ecu can provide an accurate falling edge signal to trigger the spark event, but there is no easy way to also provide dwell control via the trigger signal given the limited timer resources. Looks like I'll have to use one of those 4-wire GM ignitors for dwell purposes. Thanks again for the info. Very informative thread.
05-23-2004, 02:29 PM
#50
Senior Member
Join Date: Nov 2003
Posts: 480
I just checked 4 lead ignitors - all appear to be the dumb variety.
3 are part # N327-18-100. I believe there is also another part # out
there. My 4th one is plainted black, so the label can't be read. I do
recall seeing that some have the resistor on the + side of the coil,
some have it on the - side - I don't know if maybe this is the difference
between the part #'s.
I found a page somewhere that had scanned instructions from a discontinued
CD ignition kit that looked really neat. If I find it I'll post it.
3 are part # N327-18-100. I believe there is also another part # out
there. My 4th one is plainted black, so the label can't be read. I do
recall seeing that some have the resistor on the + side of the coil,
some have it on the - side - I don't know if maybe this is the difference
between the part #'s.
I found a page somewhere that had scanned instructions from a discontinued
CD ignition kit that looked really neat. If I find it I'll post it.