I have the standard Mercury ignition system and distributor on my 500hp. I was planing on changing to a MSD system. Should I use the original distributor with the MSD box or change the whole system out?
Also dosn't MSD make an ignition box that has the rev limiter built right in it?
What would be the hp gain on a MSD system?
Thanks,
Mike

Keep the merc distributor and run the crane marine box have had better luck with them and has rev limiter built in plus 6 merc advance curves. Jegs sells them.

MSD......Reliability down the $hitter. Be sure to keep your old stuff handy.

Heat.

Mount the MSD to an aluminum plate located near airflow. Don't use the rubber feet. There's a reason why they are failing.

They also offer no advantages over the TB4 in a NA 5500 rpm application. They work well in 6000+ rpm apps, and do an excellent job keeping the idle clean on blower motors running cold spark plugs. Also very helpful in high boost (over 12 psi) applications.

Keep the Mercury for your application. If you go with the MSD, I would keep the Mercury onboard as a spare.

So it sounds like the original equipment is more reliable.

What I was looking for was something to just give me a little better burn to clean it up. I also wanted to replace the old black coil that is on it with some thing a little nicer to look at.

Feel free to replace the coil with whatever you like. Won't hurt anything.

Is there any real gains changing the ignition system to more of a higher out put, performance Idling etc.?

not if the motor is stock.

Is there a way to increase the rev limiter on the TB 4?