Originally Posted by jseabolt
I thought an MSD ignition system replaced the factory control module. I mean the box is big enough to run an aftermarket fuel injection system as well as the ignition. What would be the reason behind running an MSD control box in conjunction with an HEI, Duraspark, Bosch, etc. control module?
All the MSD does is intercept the signal from the distributor to the coil and amplify it. It causes a multiple-spark-discharge(msd) so that the plug fires several times milliseconds apart. This is only done in lower RPM range where there is enough delay in crank degrees for it to happen.
With the BTM feature, it not only intercepts, it delays the signal as boost comes up. This is done in a smooth, linear curve based on the retard-per-lb-boost knob mounted in the cab and is MUCH better than the pull-all-at-once setup you have now So, you can vary it from very little to alot depending on what the engine likes instead of being all in or all out.