Ignition Coil

I was looking at ignition coils on the Petronix website and noticed that the Flamethrower 40K coil is available in two different primary resistance values. Either 1.5 ohm or 3.0 ohm versions are available. They note that they are internally resisted so I understand that one would feed 12v+ directly to it and not use the ballast resister on the Jeep firewall. How does one choose the primary resistance value? I tried to look this up on the web but I am still confused. The application would be for a 225 V6. I see that their application chart indicates to use the 3.0 ohm version for 4 & 6 cylinder, but I want to know why. Perhaps something to do with dwell time?? This is for my personal knowledge purpose rather then just finding the suggested value coil on their chart.

Petronix info from their webpage;
While it's the perfect coil to go with the PerTronix Ignitor breakerless ignition, our 40,000 volt Flame-Thrower canister coil can benefit virtually any distributor type inductive system. Its higher voltage allows larger spark plug gaps for added power, smoother response and better fuel economy. These coils are internally resisted so they are compatible with many ignition systems.

Our oil filled coils offer great heat control for street driven vehicles, while our epoxy filled coils provide superior winding support for high vibration environments in offroad vehicles and boats.

Features

• 40,000 volts
• Available chrome plated or black for that "stock look".
• For use with inductive ignition systems.
• 1.5 or 3.0 Ohm primary resistance values available.
• Legal in all 50 states and Canada. (C.A.R.B. E.O. #D-57-10)
• Warranty: 90 Days

 

For those who may be curious...the link below kind of explains the info I was looking for.
This is somewhat of a long thread to read but interesting info about coil input resistance & voltage input.
http://www.moyermarine.com/forums/showthread.php?t=5748