Need some help - ignition options for mercruiser v8

[Mootspoints]

Quick background.  Recently acquired a '79 CVZ-18 sight unseen.  There's a lot of other background, but currently working on an ignition problem.

The engine is labeled as a 228, but the prior owner reported that he put in a 350 short block after the motor wasn't winterized and cracked the block (I'm hoping not an automotive, but who knows).  The distributor / ignition had been replaced with a generic, integrated coil automotive distributor.  It had a weird issue where it got spark to start, but lost spark as soon as the ignition key went back to run.  I pulled and reinstalled the coil and it started working again...  Who knows about that.  Anyway, it's also running really rough at low RPM after driving it around a while.  My theory is that there might be high humidity / moisture in the distributor cap as it's not a sealed unit and there is some misfiring going on.  I'm not certain, but either way I don't like having this non-marine ignition in the boat.

So my question: what is the best option for replacing the ignition on this thing?  Back to a thunderbolt?  If so, what components do I need?  Is there a better aftermarket option I should look at?  I'm not super concerned about cost, but I also don't want to spend $600 if it doesn't come with any performance advantage.

Thanks!

[carlsoncvx18]

I would look into a pertronix  distributor you need a coil to goo with it. Converted my points ignition to there bolt in set up never have a problem. 

[thedeuceman]

I?m not sure when they switched to the thunderbolt on the Chevy motors, but If the 79 originally came with a points distributor, there?s a ballast resistor (resistance wire) lurking in the wiring harness. if that?s in there, the HEI style ignition would have problems, and the spark, while cranking would also be explained because it?s bypassed when the starter solenoid is pulled in.
And I agree with Jeff on the pertronics.


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[Plugcheck]

It is important to run a marine rated distributor even if the points are replaced with an aftermarket ignition module.    Lots of sparks floating around inside that cap should any fuel vapors be hiding in the bilge.    Joe is correct concerning the ballast resistor, it limits the current in the coil during run, but is often bypassed when cranking for a bit more spark.     I also have a 79 cvz-18 running a Mallory dizzy with pertronix 3 and pertronix super coil, crab cap/rotor.    My dizzy was points on the 898(305 2bbl).  Have had no issues in nearly 10 years ignition wise, just don't use solid core wires, use suppression type.    Pertronix and other solid state ignitions don't tolerate the emi/rfi very well.     Good luck, post pictures!

[Mootspoints]

Hmm?. Thanks all.  Know where I can find the ballast resister and can it be removed if there?  The engine was originally a 228 305 4bbl.  It does run, but sometimes not well. 

What coil should I source with the pertronix?

Will get pictures soon.

[Plugcheck]

Go with the coil that matches the electronic ignition.   I bought my pertronix as a package ignitor/coil, then you are assured of the hottest spark and compatibility.

[Mootspoints]

Okay, ordered from Jegs.  Will be here Thursday and report back how it works out.

[Mootspoints]

Closing this out.  Had a couple unforeseen roadblocks, but finally got the new ignition in yesterday and got the boat on the water.  Wow!  What a difference it made.  Idle is better, acceleration is waaaay better and the whole thing just works 100% better than it was with the weird auto HEI unit.

Used a pertronix distributor, pertronix 8mm wound RF resistant wires, pertronix flame thrower coil.  Changed all the spark plugs to factory AC Delco and gapped to .040 (+.005 over factory per pertronix instructions).  Left the silver springs in the mechanical advance which is supposed to start advance at 1k and have full advance to +24degrees by 2k.  Set at 8 degrees at idle.

I think I can go more aggressive on the timing still, but for now it?s great as is.  Thanks for the help!

[Plugcheck]

Most of the SBC engines like 28-32 degrees total advance.   Great to hear you're back up and running, go enjoy some time with your CVZ.

[demian5]

Personally its easier and cheaper to have another set of points and condenser on hand than a spare petronix...

Just sayin...