How to Tell Ignition Coil Compatababilty

I recently had an ignition module fail and through the process replaced stock coil with MSD Master Blaster Coil. Stock coil had a slight oil leakage around the crimped lid. I know there are some different coils out there, I know there are coils for electronic ignitions and some for points style. Is that all there is too them? I checked the ohm readings of my new high output MSD Master Blaster coil. The primary side is inline with factory coil readings per my factory manual. (1.5-->2.0 ohm) but the secondary side is about 5k and factory specs are 9-10k. Hopefully the new coil is compatible with my ignition. Any thoughts from experts? Am I OK to keep the MSD coil?

Re: How to Tell Ignition Coil Compatababilty

The primary compatibility issue is whether a coil is expecting EXTERNAL BALLAST or has its' own INTERNAL BALLAST.

Most "black" stock coils will have that stenciled on it somewhere. Your ignition system will, based on design, either have ballast resistance in the circuit via resistance wire or actual resistor component, or it will not have any. If it has resistance in the circuit then use a coil that is spec'd for EXTERNAL BALLAST. If no resistance then it is expecting that a coil with INTERNAL BALLAST will be used (or a coil that does not require any ballast, see next paragraph).

Some newer design coils do not need resistance and in the bulk of ignition systems out there they can be used and the resistance component removed from the circuit. I know Jacobs has coils like this, and I am certain there are others.

As far as Marine vs. Automotive, it is really more of an Off-Road/Marine vs. Standard duty. Off-road/Marine/Severe Duty coils are packed differently inside and are made to withstand much more physical jostling and jarring abuse. The actual electrical performance from the coil is the same.

Re: How to Tell Ignition Coil Compatababilty

The blaster coil should be fine, just be sure your cap and wires are of high quality and in good condition. If it is the one I am thinking of it has a tall tower, which is good, and is a good choice. I use that blaster on one of my MoPar hotrods with a stepped up but stock type electronic ignition and with a stock ballast resistor, works great from idle all the way past 6,500rpm.

The coil is expecting a certain ballast resistance on the primary terminal. As long as that is within the range that MSD spec'd for the coil then you are good to go. The secondary reading you are getting indicates the coil is designed to put out more voltage for spark than a stock one. Giving the coil what it wants on the primary side is what you need to focus on.

Re: How to Tell Ignition Coil Compatababilty

Maclin said:

The blaster coil should be fine, just be sure your cap and wires are of high quality and in good condition. If it is the one I am thinking of it has a tall tower, which is good, and is a good choice. I use that blaster on one of my MoPar hotrods with a stepped up but stock type electronic ignition and with a stock ballast resistor, works great from idle all the way past 6,500rpm.

The coil is expecting a certain ballast resistance on the primary terminal. As long as that is within the range that MSD spec'd for the coil then you are good to go. The secondary reading you are getting indicates the coil is designed to put out more voltage for spark than a stock one. Giving the coil what it wants on the primary side is what you need to focus on.

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I read this right after I got off phone with MSD. Either I got a guy that was having a case of the Fridays or their customer service suks. He wouldn't tell me anything. Answered like he was totally reading from script. Eventually I asked him if I was understanding ignition theory is that as long as the primary side resistance is same I cant hurt module and he said "yes...in theory, but he is still not sure my new coil is OK". WTF.

Based on my thoughts and what you said I think I am A-OK. If it was not tough to replace (back of the motor, risers need removed etc.) I would throw the thing away and buy an OEM.

Thanks, since primary side is within factory spec , I think I am fine.