Ok, I've seen a couple of interesting setups listed on here as to how you can actuate your 6PI system on an S4 once you've screwed with the exhaust.

Here's what I'm wondering - why is it this involved? Could the setup from the S5 be retrofitted? I do know that one thing the S4s lack is an RPM signal, but doesn't MSD make something that does this, for relatively cheap?

What is the best way to do this? I know it's been discussed in various spots on the board but I'm wondering if there's a general consensus.