I'm not suggesting they don't work. I run cd ignitions and very happy with them. I know the 525sc, 600sc, 800sc ran merc ignitions, and unless someone messed with the carbs, plug fouling was not an issue. The thing I like is having the ability to change timing curves, which you really can't do with a merc ignition

MSD recommends to run a noise filter to keep the voltage spikes from taking out the box. I have had msd on my boat for 10 years no problems yet. As for the rust I put extra vents in the dist. cap it seemed to help some. I hope I did not jinx my self with this post!

If you are asking if you need to run a box, the answer is no, you will not run any faster, if may or may not clean up the idle..depends on carb/cam, timing...the only real gain would be a rev limiter if box has one and you feel you need one, you can buy one of the cheap HP HEI, and run fine, used several of them and the only real fail item(and I have never had one fail) is the module and you can keep a spare and change very easily...Rob

the msd box does give you more duration of spark,,7* to be exact so the spark stays their a little longer at idle then a regular distributor would..they usually cut out at 3500 rpms..the only reason i have one is because the temperature drop on the lakes and rivers i run and they are not constantly the same..it can vary up to 20* sometimes and i dont run a thermostat,,just a restrictor plate..i just got sick of constantly adjusting my carberator,,and hollys are cold harted *****s..

Reviving this thread.
Time to buy an ignition system.
Anyone have experience with the msd "ready to run" distributors? No box and retail at around 400 bones.
I'm seriously considering the mallory marine electronic distributor but it would need an "add on" rev limiter.

Anyone running the mallory marine unit?

Thanks, rob

If I had 400 to spend, I'd go with the Mallory pro billet dist, which is identical to msds pro billet but cheaper, and a crane ign box. That would be about same cost but better ignition imo. Or possibly the Mallory pro billet with the msd 6 programmable box for a very tunable timing curve

How would the DUI stack up to those?

Wow I thought mine was bad the first time I took it apart. I call MSD they said they know about the corrosion issue. But had no solution for it. There are vents in the bottom mine were plugged up. After the rebuild my builder suggested drilling the cap and did so thru one of the towers that excepted the screws for the wire hold down that I do not use.

Not to hijack the thread. Where do most people mount their box. Mine is on the transom. Do the engine mounted boxes cause the for mentioned failures heat and vibrations?

Msd boxes are junk plain and simple. Doesn't matter where you mount them. You can have a brand new box that doesn't work. Doesn't matter if it Auto or Marine they are junk.

I'm using a Jesel front mount distributor and Daytona box on my new build.

mallory version 154.99

http://www.jegs.com/i/Mallory/650/85551M/10002/-1

MSD version 249.99

http://www.jegs.com/i/MSD+Ignition/121/85551/10002/-1