Re: Merc 7.4 330 to 502 Ignition change
 

I Just Put The 502/502 Cam In My 330hp And Had To Change The Dist. I Would Recomend Doing So. The T-bolt Iv Should Be Fine. If Not I Think I Have A Msd 6m-2 Around Here I Could Let Go Cheap.

Re: Merc 7.4 330 to 502 Ignition change
 

The 502/502 is reputed to be a bad choice because of its 110 lobe centers, which promote reversion and suching water up the exhaust. I chose a Ultradyne cam with 114 centers and a bit more performance. Don't forget to change the dist gear to the GM melonized unit for roller cams, PN# 10456413, cheap insurance. Y should have a Tbolt V (has a knock sensor on side of block) since your boat was a 96, you do have a rev limiter at 4700. What I did when I used my 95 Tbolt V unit was to swap out the module on the side of the distributor for the 500 HP bulldog merc unit, worked perf for me, mine revs to 6000 by the tach. (unplug the knock sensor if using the bulldog 500 module, I forget why). Good luck on your project.

Re: Merc 7.4 330 to 502 Ignition change
 

Yeap... I have already tapped and moved the knock sensor to the new block so it sounds like you guys are on there (as it there was a knock sensor on my old block that I relocated).

By U... I may be intrested in that MSD anyways... could you PM me with info?

LT1.. wow, Now you got me thinking about that Cam... Is anyone else familar with this problem too?

Re: Merc 7.4 330 to 502 Ignition change
 

I WILL LOOK FOR IT THIS WEEKEND. FOR SOME REASON I THINK IT MAY BE ON MY BOAT WHICH IS IN NEW ORLEANS UNTIL WED OF NEXT WEEK. I WILL LET YOU KNOW.

AS FOR REVERSION I AM NOT TOO WORRIED B/C MY NEW EXHAUST HAS A WATER TRAP AND WATER EVAPORATION POCKETS.

Re: Merc 7.4 330 to 502 Ignition change
 

A 1996 7.4L low output engine would have a thunder bolt V ignition with a rev limiter at around 4800rpm. You will need a different ignition module.
Try to get your hands on one from a 454Mag or 502Mag if you don't want to spend the $$ for an aftermarket ignition.
If your 7.4L is/was a Gen VI roller cam engine, the distributor gear will work in the new engine. If the 7.4L is a Gen V with a cast flat tappet cam, you will need a new gear.
As for the ZZ502 cam, there has been lots of debate how it is not a great marine cam, however, there are many guys running them with success.

Re: Merc 7.4 330 to 502 Ignition change
 

By U... got it thanks. I am considering on springing for the CCPerformance marine package for $699 that includes the Marine MSD ignition mod, MSD rev limiter, billit marine dist... etc.

Pat... Good info... I am thinking more and more that I just need to spring for the MSD setup. Any thoughts?

Re: Merc 7.4 330 to 502 Ignition change
 

My personal opinion is that the MSD stuff is overpriced. I 've also heard lots of guys here on OSO complain about failure. The MSD stuff it is less reliable than the Merc Thunderbolt for sure.
If I was in your shoes and new is the call, I'd buy a DUI unit. $300 gets you a new distributor with a built in coil ready to drop in. Another $130 if you want to add on a rev limiter.

Re: Merc 7.4 330 to 502 Ignition change
 

Well I went DUI for the Dist and rev limiter... I hope this is worth the $$$... any tips on install?

Re: Merc 7.4 330 to 502 Ignition change
 

Good choice. I've been running 2 DUIs for over 15 years. No problems.
Gary

Re: Merc 7.4 330 to 502 Ignition change
 

Where did you get the DUI and can you share the part number?
Thanks