MSD Coil replacement

[rod locker]

Looking to replace stock coil in 1974 318 with a MSD Blaster 2. Everything else will remain the same for now. Are there any problems that I may run into with this swap? Should be pretty straight forward.

 

[JR]

Unless you think a hotter/stronger spark is a bad thing,nope! I have been running a Blaster 2 on my stock slant daily driver and not had one problem.

 

[ramcharger]

Here's the deal with "hotter" coils. Coils are built with a rev range in mind. The stock coils are meant to provide a great spark from idle to around 5K where they start loosing steam. The MSD Blaster coil is meant to provide a great spark from 2500-6500+ rpm. At idle, the stock coil will provide more spark current than a MSD Blaster will with a stock ECU or points, but will start to pull away in power over 2500 rpm.

This is why multiple discharge boxes like a Mallory or MSD are recommended for use with an aftermarket coil. Under 3K, they send 3 sparks to make up for the coil's underperformance at lower rpm. Not only that, but they also surge the coil with 500-600V on the primary side vs. 12V from a points or stock style Mopar ECU.

On the other side of the coin, this is why dual point distributors were used on hp offerings from the factory as the increased total dwell angle allowed the stock coil more time to charge increasing the stock coils ability to provide a sufficeint spark at higher rpm. What does this mean to you? IMHO, I wouldn't bother replacing the stock coil with an aftermarket coil unless you are using a multiple spark discharge style ignition box. It won't hurt anything but you won't be gaining anything in spark energy below 2500 rpm.

Oh yeah, I want to add that the MSD oil filled coils should be mounted right side up, not on their side. They used to offer an epoxy filled coil that could be mounted in any position, but I don't know if they still do.....Yep they do, it's part number 8222.

 

[MadScientistMat]

Here's the deal with "hotter" coils. Coils are built with a rev range in mind. The stock coils are meant to provide a great spark from idle to around 5K where they start loosing steam. The MSD Blaster coil is meant to provide a great spark from 2500-6500+ rpm. At idle, the stock coil will provide more spark current than a MSD Blaster will with a stock ECU or points, but will start to pull away in power over 2500 rpm.

My boss once did a test on a GM coil vs an MSD coil and in that particular case, the results were a bit different. We monitored both the coil current draw and the secondary voltage. This test was done with a variable dwell angle HEI module, so you would get a different curve with a Mopar system, but I'd expect the same trend.

The MSD coil drew more current across the board. So this coil would give you more spark energy at idle and at the top end. However, this engine didn't really like to rev out very well, didn't make a lot of cylinder pressure, and so it didn't really have any need for a hotter ignition system. I don't expect any problems with the coil upgrade here, but whether you will benefit depends on what mods you have.

This is why multiple discharge boxes like a Mallory or MSD are recommended for use with an aftermarket coil. Under 3K, they send 3 sparks to make up for the coil's underperformance at lower rpm. Not only that, but they also surge the coil with 500-600V on the primary side vs. 12V from a points or stock style Mopar ECU.

The voltage is definitely one of the key reasons the boxes use a different coil. However, it's the box, not the coil, that underperforms at low RPM. A CDI box's spark does not burn as long as a stock ignition, so it compensates by adding more of them.

Oh yeah, I want to add that the MSD oil filled coils should be mounted right side up, not on their side. They used to offer an epoxy filled coil that could be mounted in any position, but I don't know if they still do.....Yep they do, it's part number 8222.

Good point, oil filled MSD coils should never be installed sideways. I've seen one self destruct when installed upside down and the oil leaked out.

 

[EL5DEMON340]

My instruction manual on my blaster said nothing about horizontal mounting, tons of us are running them that way, just make sure your + & - posts are horizontal too.

 

[ramcharger]

My instruction manual on my blaster said nothing about horizontal mounting, tons of us are running them that way, just make sure your + & - posts are horizontal too.

You need to read a little closer:

"It is recommended to mount the PN 8202 and 8223 coils in an upright
position. The High Vibration Coil, PN 8222, can be mounted in any position due to its epoxy potting
compound."


I don't understand your comment in regards to the primary terminals as they are in a fixed position

 

[ramcharger]

My boss once did a test on a GM coil vs an MSD coil and in that particular case, the results were a bit different. We monitored both the coil current draw and the secondary voltage. This test was done with a variable dwell angle HEI module, so you would get a different curve with a Mopar system, but I'd expect the same trend.

I would not expect the same results as the HEI ignition as they are two different animals. No varible dwell with the Mopar box and a good HEI module can handle a coil draw of over 5.5 amps of current, Even exceeding 7 amps with an aftermarket HEI module. Also, there is no ballast resistor used.

The MSD coil drew more current across the board. So this coil would give you more spark energy at idle and at the top end. However, this engine didn't really like to rev out very well, didn't make a lot of cylinder pressure, and so it didn't really have any need for a hotter ignition system. I don't expect any problems with the coil upgrade here, but whether you will benefit depends on what mods you have.

Again, we have apples and oranges here. A MSD HEI coil can't be compared to a Blaster II and a Mopar orange box with a ballast resistor delivering only 9V on the primary. A coil can't draw any more then an inductive Mopar ECU can handle.

The voltage is definitely one of the key reasons the boxes use a different coil. However, it's the box, not the coil, that underperforms at low RPM. A CDI box's spark does not burn as long as a stock ignition, so it compensates by adding more of them.

I agree that an inductive style ignition has a longer duration spark than a CDI, but I wonder if your statement holds true in regards to the box vs the coil. If it did, it would be much more apparent at high rpm vs. low rpm, yet the multiple spark is discharged only below 3K. Mallory even rates their coils on expected rpm use.

Good point, oil filled MSD coils should never be installed sideways. I've seen one self destruct when installed upside down and the oil leaked out.

Exactly.

Matt, I also want to say that your input on this subject is greatly appreciated and as you can tell, I love a good debate. Great graphs and the MSD handily outperforms the stock HEI coil in both consistency of spark and power delivered. What I found was seen on a Sun oscilloscope way back in the mid 80's with a Accel super coil vs. a stock coil and a dual point distributor. We both know how a transformer works and the more current that can be pulled across the primary windings, the more potential power at the secondary winding given the same ratio of windings. I wonder if this increased pull across the primary could also cause longevity problems with the Mopar box?

 

[EL5DEMON340]

You need to read a little closer:

"It is recommended to mount the PN 8202 and 8223 coils in an upright
position. The High Vibration Coil, PN 8222, can be mounted in any position due to its epoxy potting
compound."


I don't understand your comment in regards to the primary terminals as they are in a fixed position

My instructions do not say that, granted they are about 15 years old so maybe they were made better. As to the terminals if you are going to use the stock coil mount on a big or small block then the coil is in the horizontal position, you want to make sure the terminals are also horizontal, not one hood side and other intake side. just my two cents...

 

[684mulas]

MSD recommends that you change to a 0.8 ohm ballast resistor. My understanding is that it will provide protection to your ignition control box. I followed the recommendation to be sure and have had no problems.

 

[ramcharger]

My instructions do not say that, granted they are about 15 years old so maybe they were made better.

That's most certainly a possibility. I do recall a similiar warning on Accel super coils from back in the mid 80's.

As to the terminals if you are going to use the stock coil mount on a big or small block then the coil is in the horizontal position, you want to make sure the terminals are also horizontal, not one hood side and other intake side. just my two cents...

OK, I understand where your coming from now but why would this hold true? I always mounted the stock coil in this manner but just considered it a way to keep the primary terminals away from any possible path to ground.

MSD recommends that you change to a 0.8 ohm ballast resistor. My understanding is that it will provide protection to your ignition control box. I followed the recommendation to be sure and have had no problems.

Yes! A ballast resistor must be used with a Mopar ECU.

 

[MadScientistMat]

I like a friendly debate too. Your response raised a couple interesting questions about the Mopar ignitions.

Again, we have apples and oranges here. A MSD HEI coil can't be compared to a Blaster II and a Mopar orange box with a ballast resistor delivering only 9V on the primary. A coil can't draw any more then an inductive Mopar ECU can handle.

The ballast resistor is the biggest factor that I'm unsure of here. It does seem like it would do more to limit current at low RPM than at high RPM, and an aftermarket coil could possibly heat it up more from more current draw, making the coil self-defeating until you bring the RPM up. Would it be more accurate to say the coil can't draw more current than the ballast resistor allows?

I agree that an inductive style ignition has a longer duration spark than a CDI, but I wonder if your statement holds true in regards to the box vs the coil. If it did, it would be much more apparent at high rpm vs. low rpm, yet the multiple spark is discharged only below 3K. Mallory even rates their coils on expected rpm use.

It does seem a bit weird that the ignition would have an easier time lighting off the mixture at high RPM than at low RPM, but that often seems to be the case. With no ballast resistor and no dwell - just emptying a capacitor - the spark energy is the same across the rev range, or at least it should be.

Matt, I also want to say that your input on this subject is greatly appreciated and as you can tell, I love a good debate. Great graphs and the MSD handily outperforms the stock HEI coil in both consistency of spark and power delivered. What I found was seen on a Sun oscilloscope way back in the mid 80's with a Accel super coil vs. a stock coil and a dual point distributor. We both know how a transformer works and the more current that can be pulled across the primary windings, the more potential power at the secondary winding given the same ratio of windings. I wonder if this increased pull across the primary could also cause longevity problems with the Mopar box?

It wouldn't surprise me if that was the case. Unless there's a thermal shut down or the ballast resistor puts an absolute limit on the current, most transistors can be damaged if you overheat them from too much current. Or, depending on the internal construction of the box, something else may get damaged - it's possible that some of the internal connections may be the limiting factor.

 

[ramcharger]

I like a friendly debate too. Your response raised a couple interesting questions about the Mopar ignitions.
The ballast resistor is the biggest factor that I'm unsure of here. It does seem like it would do more to limit current at low RPM than at high RPM, and an aftermarket coil could possibly heat it up more from more current draw, making the coil self-defeating until you bring the RPM up. Would it be more accurate to say the coil can't draw more current than the ballast resistor allows?


Well, according to ohms law a resistor will limit both current and voltage. I agree that there is a self defeating property built in to the mopar style ballast resistor. I have put a Blaster 2 on with a Mopar ecu and that ballast got way freaking hot, far too hot to touch in fact and of course the resistance increased.

It does seem a bit weird that the ignition would have an easier time lighting off the mixture at high RPM than at low RPM, but that often seems to be the case. With no ballast resistor and no dwell - just emptying a capacitor - the spark energy is the same across the rev range, or at least it should be.

Agreed. Something interesting I came across in an engineering study of the MSD 6AL2 is that they (MSD) calculates the spark energy in mj at 1500 rpm adding the energy of all the sparks vs just a single discharge. I'm guessing that all manufacturerers do the same. Seems a bit disingeniuos as high rpm spark is what we, as hot rodders, are most concerned with. I you are interested, PM me with your e-mail and I'll send you the .pdf It's too big too load up here.

My educated guess in regards to the CDI performing so much better in a high performance engine at high rpm lies with the ability to provide a major whack to primary coil without having to wait for the coil to saturate. At higher rpm the longer spark duration is not necessary due to the minimized time of the compression cycle. I also believe that that "whack" can provide the coil with enough voltage to jump the gap at very high cylinder pressures where an inductive ignition just doesn't have the time to pull it off. Make sense?



It wouldn't surprise me if that was the case. Unless there's a thermal shut down or the ballast resistor puts an absolute limit on the current, most transistors can be damaged if you overheat them from too much current. Or, depending on the internal construction of the box, something else may get damaged - it's possible that some of the internal connections may be the limiting factor.

I agree with you here. I think Don at 4 Seconds Flat has built a new box with upgraded transistors and circuitry and I've heard good things about his products but I have no personal experience with them. I do want to get my MP distributor phased by him as my distributor shows signs of being way off.

 

[MadScientistMat]

Well, according to ohms law a resistor will limit both current and voltage. I agree that there is a self defeating property built in to the mopar style ballast resistor. I have put a Blaster 2 on with a Mopar ecu and that ballast got way freaking hot, far too hot to touch in fact and of course the resistance increased.

Wow. There goes all the extra ignition power...

Agreed. Something interesting I came across in an engineering study of the MSD 6AL2 is that they (MSD) calculates the spark energy in mj at 1500 rpm adding the energy of all the sparks vs just a single discharge. I'm guessing that all manufacturerers do the same. Seems a bit disingeniuos as high rpm spark is what we, as hot rodders, are most concerned with. I you are interested, PM me with your e-mail and I'll send you the .pdf It's too big too load up here.

That is a bit disingenuous, though there are probably a lot of guys who seldom take their MSD equipped ignitions out of the multi spark range. Sending PM now.

My educated guess in regards to the CDI performing so much better in a high performance engine at high rpm lies with the ability to provide a major whack to primary coil without having to wait for the coil to saturate. At higher rpm the longer spark duration is not necessary due to the minimized time of the compression cycle. I also believe that that "whack" can provide the coil with enough voltage to jump the gap at very high cylinder pressures where an inductive ignition just doesn't have the time to pull it off. Make sense?

That's definitely a big part of it, capacitors charge faster than coils. CDI ignitions evidently have the voltage at the plugs build faster too. Getting the same amount of spark energy you'd squeeze out of an MSD box at high RPM with an inductive system would require multiple coils like on newer OEM applications.

I agree with you here. I think Don at 4 Seconds Flat has built a new box with upgraded transistors and circuitry and I've heard good things about his products but I have no personal experience with them. I do want to get my MP distributor phased by him as my distributor shows signs of being way off.

Sounds like an interesting project. There's a lot of new developments with transistors and other parts out there that could be stuffed in the classic Mopar box; some of the new ignition transistors can handle 20 amps of current.

 

[rod locker]

Gee.......now I am all confused. My 318 has a new ballast resistor and ignition module.....and everything else electically is stock. I changed those just because. I haven't looked but am pretty sure car still has points. It is a 1974 model Duster. Haven't had the car long and was going to change the coil while changing the intake. But now I am not sure. Electircal work....and trouble shooting scare me to death. So now I don't know what to do.

 

[green1]

Good point, oil filled MSD coils should never be installed sideways. I've seen one self destruct when installed upside down and the oil leaked out.
Hmmm, I have a factory one installed upside down for over 25 years.....and it still works.

 

[ramcharger]

Gee.......now I am all confused. My 318 has a new ballast resistor and ignition module.....and everything else electically is stock. I changed those just because. I haven't looked but am pretty sure car still has points. It is a 1974 model Duster. Haven't had the car long and was going to change the coil while changing the intake. But now I am not sure. Electircal work....and trouble shooting scare me to death. So now I don't know what to do.

If you have a Mopar ECU, you don't have points, you have a magnetic pickup style distributor. I'd leave the coil alone if it's still working fine. If the 318 is stock, you wouldn't really see a gain anyway. If you plan on adding NOS or otherwise increasing cylinder pressure (horsepower), go ahead and add the coil but use their (MSD's) recommended ballast resistor and order a second one to keep in the glovebox. The nice thing about the Blaster 2 is that if you do upgrade to MSD's or another manufacterer's CDI box, the coil will be compatible and you can dump the ballast resistor. I hope this clears things up as Matt and I got into some pretty heavy theory.

 

[ramcharger]

Good point, oil filled MSD coils should never be installed sideways. I've seen one self destruct when installed upside down and the oil leaked out.
Hmmm, I have a factory one installed upside down for over 25 years.....and it still works.

A factory MSD?

 

[green1]

Factory coil; must be better than a MSD that can't be horizontal, or upside down.

 

[ramcharger]

Factory coil; must be better than a MSD that can't be horizontal, or upside down.

I'm thinking that it doesn't pull as much current, hence cooling isn't as important.

 

[rod locker]

Thought I would call MSD and get their opinion on this subject. I was told by MSD that the coil (blaster 2) could be mounted either horizontally or vertically with stock ignition. However,with a MSD ignition he told me to mount it vertically because the MSD ignition would cause more heat in the coil itself. So I guess I will go ahead and install the MSD coil and mount it vertically if possible.......Thanks for all the good info.......always learn a lot from this forum.........Thanks again