Built In Coil/Distrib. or Pro-Billet & MSD Blaster 2 Coil??
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Joined: Jan 2006
Posts: 66
Built In Coil/Distrib. or Pro-Billet & MSD Blaster 2 Coil??
I have a 383 stroker motor in my 67 Camaro...
Its got a MSD 6A box and a MSD distributor w/ a built in coil.. My question is I have the ability to swap a MSD Pro-Billet dist. PN 85551 with a MSD Blaster 2 Coil for my distributor and cap...
Should I do this? Is there a big advantage to using this?
Its got a MSD 6A box and a MSD distributor w/ a built in coil.. My question is I have the ability to swap a MSD Pro-Billet dist. PN 85551 with a MSD Blaster 2 Coil for my distributor and cap...
Should I do this? Is there a big advantage to using this?
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Joined: Oct 2006
Posts: 370
From: Oviedo FL
Is the distributor you have now vacum advance? That probillet part # is a mechanical advance. If your car is a street car and your existing distributor is vacum advance then i would stay with that set up.
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Joined: Dec 1969
Posts: 1,147
From: Phila., PA
The primary problem with the coil-in-cap design is that the coil can overheat- not that it lacks the energy capacity to get the job done (if you have chosen a coil that's appropriate for your application). If you aren't killing coils from heat I don't think there's much performance to be had.
Oil-filled external coils were used with points-type ignition systems back in the day becuase they had no capacity to adjust the dwell or limit current through the coil at lower RPMs. The coil would energize and just "bake" at low RPMs as the current ramped up between firings with no limit in sight (that's also one of the reasons why points type ignitions used a resistor wire or a ballast resistor on the power wire to the coil- it helped prevent frying the coil when you were just tooling around town). External coils with the windings suspended in oil could dissipate this heat fairly well.
When GM went to the HEI ignition they incorporated both variable dwell circuitry AND current limiting circuitry into the ignition module to get around these shortcomings in points-type ignition systems. (FYI- this was really high-tech stuff back in 1974 when the HEI first hit the streets!!). That's the whole reason they could get away with the tiny little coil mounted on top of the distributor. If you tried to use that same coil with an earlier points-type ignition you're fry it like a potato chip very quickly.
When you change over to a CD-type ignition like the MSD box ALL the rules change. The coil is no longer fed current constantly and then shut off when it needs to fire (like a points-type ignition or HEI does). It is hit with a big jolt of juice at the exact moment it needs to be fired and sits there unused the rest of the time. I am no ignition expert so I can't say how this might affect the amount of heat generated in the coil, but I can say I've never had a problem firing an in-cap HEI coil with an MSD box and the coil always seems to last as long or longer than the ignition box ever does!
Oil-filled external coils were used with points-type ignition systems back in the day becuase they had no capacity to adjust the dwell or limit current through the coil at lower RPMs. The coil would energize and just "bake" at low RPMs as the current ramped up between firings with no limit in sight (that's also one of the reasons why points type ignitions used a resistor wire or a ballast resistor on the power wire to the coil- it helped prevent frying the coil when you were just tooling around town). External coils with the windings suspended in oil could dissipate this heat fairly well.
When GM went to the HEI ignition they incorporated both variable dwell circuitry AND current limiting circuitry into the ignition module to get around these shortcomings in points-type ignition systems. (FYI- this was really high-tech stuff back in 1974 when the HEI first hit the streets!!). That's the whole reason they could get away with the tiny little coil mounted on top of the distributor. If you tried to use that same coil with an earlier points-type ignition you're fry it like a potato chip very quickly.
When you change over to a CD-type ignition like the MSD box ALL the rules change. The coil is no longer fed current constantly and then shut off when it needs to fire (like a points-type ignition or HEI does). It is hit with a big jolt of juice at the exact moment it needs to be fired and sits there unused the rest of the time. I am no ignition expert so I can't say how this might affect the amount of heat generated in the coil, but I can say I've never had a problem firing an in-cap HEI coil with an MSD box and the coil always seems to last as long or longer than the ignition box ever does!
Last edited by Damon; Apr 2, 2007 at 08:57 PM.
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Joined: Feb 2004
Posts: 51
From: Southern California
The primary problem with the coil-in-cap design is that the coil can overheat- not that it lacks the energy capacity to get the job done (if you have chosen a coil that's appropriate for your application). If you aren't killing coils from heat I don't think there's much performance to be had.
Oil-filled external coils were used with points-type ignition systems back in the day becuase they had no capacity to adjust the dwell or limit current through the coil at lower RPMs. The coil would energize and just "bake" at low RPMs as the current ramped up between firings with no limit in sight (that's also one of the reasons why points type ignitions used a resistor wire or a ballast resistor on the power wire to the coil- it helped prevent frying the coil when you were just tooling around town). External coils with the windings suspended in oil could dissipate this heat fairly well.
When GM went to the HEI ignition they incorporated both variable dwell circuitry AND current limiting circuitry into the ignition module to get around these shortcomings in points-type ignition systems. (FYI- this was really high-tech stuff back in 1974 when the HEI first hit the streets!!). That's the whole reason they could get away with the tiny little coil mounted on top of the distributor. If you tried to use that same coil with an earlier points-type ignition you're fry it like a potato chip very quickly.
When you change over to a CD-type ignition like the MSD box ALL the rules change. The coil is no longer fed current constantly and then shut off when it needs to fire (like a points-type ignition or HEI does). It is hit with a big jolt of juice at the exact moment it needs to be fired and sits there unused the rest of the time. I am no ignition expert so I can't say how this might affect the amount of heat generated in the coil, but I can say I've never had a problem firing an in-cap HEI coil with an MSD box and the coil always seems to last as long or longer than the ignition box ever does!
Oil-filled external coils were used with points-type ignition systems back in the day becuase they had no capacity to adjust the dwell or limit current through the coil at lower RPMs. The coil would energize and just "bake" at low RPMs as the current ramped up between firings with no limit in sight (that's also one of the reasons why points type ignitions used a resistor wire or a ballast resistor on the power wire to the coil- it helped prevent frying the coil when you were just tooling around town). External coils with the windings suspended in oil could dissipate this heat fairly well.
When GM went to the HEI ignition they incorporated both variable dwell circuitry AND current limiting circuitry into the ignition module to get around these shortcomings in points-type ignition systems. (FYI- this was really high-tech stuff back in 1974 when the HEI first hit the streets!!). That's the whole reason they could get away with the tiny little coil mounted on top of the distributor. If you tried to use that same coil with an earlier points-type ignition you're fry it like a potato chip very quickly.
When you change over to a CD-type ignition like the MSD box ALL the rules change. The coil is no longer fed current constantly and then shut off when it needs to fire (like a points-type ignition or HEI does). It is hit with a big jolt of juice at the exact moment it needs to be fired and sits there unused the rest of the time. I am no ignition expert so I can't say how this might affect the amount of heat generated in the coil, but I can say I've never had a problem firing an in-cap HEI coil with an MSD box and the coil always seems to last as long or longer than the ignition box ever does!
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