Hey fellas, need some advice....

I have new twin 502's moderately built, nothign special; 502's w/ TBS blowers making about 5 lbs of boost. When we did these last year we put the old TBIV ignitions on.

I bought MSD boxes, brackets, distributors, all the goods to upgrade the system... is this pretty much a direct swap? Any special concerns or anything I need to be aware of? CP Performance hooked me up with all the stuff, just wondering if there are any gotchas I need to be aware of. thanks!

There's no advantage to using the mechanical advance MSD distributors. The ones I've seen tend to rust badly inside and their sensors fail. Return them, use the Tbolt IV distributor, and Tbolt IV V6 modules. It will have a shorter advance curve, about 14 degrees, allowing for more initial advance.
Now after running that combo, see if you have plug fowling problems with extended idling. If so, you can add the MSD boxes to the Tbolt setup. Be sure to wire the MSD box with a big wire as close to the alternator/battery as you can. They have a habit of failing frequently and have been told it's due to low voltage at the box,

I appreciate that info. I already have a problem with fouled plugs from idling, and have had a lot of ignition issues last summer after the rebuilds. we checked the runout on the distributors and have realized they are kind of wearing out, I figured the MSD set up would be good. I actually bought the Hardin dist's becasue they pretty much were the same and a little bit cheaper.

Not sure about the Hardin distributors, but the Tbolts have the advantage of parts availability at the lake.
Were you running the V6 module when you had fowling problems? What was your inital and total advance?
BTW, I think I recognize your boat, have you been running it at the lake long?

I do have the V6 modules, wound up replacing them last year chasing down a problem and it turned out to not be them....
I hear ya on the parts availibility.... Total advance I think is like 30 but will need to double check... not sure on initial...

I have had about 3 years now... we run all up and down the channel from about the 1-21

Well, sounds like you need the MSDs. What's the spark advance curve on your new distributors? I'm guessing you know SC motors like a lot of initial advance. The MSD distributor uses bushings on the advance stop pins, like an old GM. If that's the case on the Hardins, use big bushings (short curve), light springs (earlier advance), and set your total advance at 30 again.
The MSD site has pretty good instructions online.

The MSD's work poorly in marine apps, like said before rust up bad inside....I ran mallory unilite before, easier to adj curve, and you want very little advance about 10-15 deg is it, then about 26-28 total, gives you more initial and will help clean the idle up and help your plug issue...Rob

I have twin 496's I built recently. There pretty stout engines and planned to you the tb1V ignition also. I like these for the simplicity as well as the low failure rate. I didn't realize you could use the msd box with that ignition. Any other real benefits to running these boxes? Also what one is the correct one for this. Seems like so many now a days,

thanks,

Well, now that Crane is up and running (i think?) again, I'd recommend avoiding anything MSD and putting the HI-6M boxes in. They hook up to the TB IV and allow you to select which curve you want on the fly.

Just my 2 cents but I thought I'd throw it out there!

Looks like the ticket. Other nice features with these are the rev limiter as well as the different advance curves. Sounds like you can use your existing module or use one of the several curves the box offers. I wonder if anyone can churp in here in regards to the performance upgrade with this or if the hotter spark ultimately helps more at just idle. HP gains?
http://www.cpperformance.com/detail.aspx?ID=9474