Mercruiser 351W HEI vs Billet Marine Distributors

Mike Mas

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Aug 22, 2016
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Hello
Here's a good topic

We have two original rebuild carb 351 Mercrusier motors going back in our 1976 28' Bertram SF ...have to get two new Distributors plus want to upgrade from points to electronic ..... Choices are get prestolites w conversion kits....or Protronix billet type marine ...both needing coils....cost over $300 per motor ...

Or the big question is why can I "not" use a new HEI ford billet distributor with the coil build in for under $100 per motor..??

No company seems to have an answer as to the difference between the Marine version and the Street Version ...both are billet both are water tight

Any feed back will help

Mike
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Because your new HEI dizzy isn't marine rated and you will blow up.

Mallory (division of prestolite ) makes new dizzys for your Ford (about $275 from summit), however if nothing wrong with your existing points dizzy, I would run points and go boating.

Marine rated are spark supressed and have been tested (SAE j1171).
 

johnkom

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Jul 26, 2004
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163
This becomes a government is here to protect your ass versus common sense. I have a 351W with a Crane Cams system. Look at the starter motor throwing sparks all over the place at start. And all they do is put a screen on it? Alternator isn't much better. But it is "Government (Coast Guard) Approved." Using an automotive "solid state" ignition system is akin to using your cell phone while pumping gas into your car. No way you have a spark and fire issue. It's just that the manufacturer doesn't want to spend the money to prove it. YMMV

JK
 

Mike Mas

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Aug 22, 2016
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So with all that said...I have been looking at the DUI marine version and even called DUI and asked them the difference and was told the advance is differant ... Nothing else all is the same....no mention of blowing up....also get this the marine is $385 and to switch the gear to counter rotating is $460.

With that said makes no sense to stay with points ...better burn and less moving parts

...looking at the Prestolite next with the conversion kit

Appreciate the input...keep it coming

Mas
 

achris

More fish than mountain goat
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.... Look at the starter motor throwing sparks all over the place at start. And all they do is put a screen on it? Alternator isn't much better. ...

A flame front can't pass through a screen with a fine mesh. That's how they are 'flash suppressed'. Marine rating doesn't mean it won't produce sparks, it means it CAN NOT start or contribute to a fire or explosion. And it's that rating that is not on automotive equipment. Water proof also doesn't mean it's flash suppressed.

Mike. If you need to buy distributors anyway, I would go to completely electronic (including the advance curve), and use the DUI dissys. No breaker plate or advance weights and springs to worry about. Merc have been using Thunderbolt fully electronic ignitions on the GM engines since 1983.....

Chris..........
 

Mike Mas

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Hey Chris
Yes we need new Dissys ....I'm deciding between the DUI HEI which is $100 more for the standard Rotation and $160 more for the Reverse Rotation compared to the Pertronix Marine Flame Thrower w 45000 v coil dissys ...

What's the pros and cons of ether ?

Thanks Mike
 

achris

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Pertronix uses the old breaker plate with weights and springs. That alone would push me away from the Pertronix.
 

Mike Mas

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Ok so there is a split w the members regarding this question....so if you guys would not mind giving your choice the Pertronix or the DUI HEI ....both marine dissys ..why and or why not ...especially why not on the Pertronix .....considering a couple things the Pertronix is $750 and the DUI is $1050 for the pair including wires and coil ....not including plugs which the DUI says to use platinum on theirs

Also this is a 28 Bertram not a race boat

Thanks for the input
Mike
 

achris

More fish than mountain goat
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Anything that does away with moving parts (especially in a salty marine environment) is a bonus in my opinion. The Pertronix uses the existing breaker plate with weights and springs for the advance. The DUI is fully electronic, including the advance.... Merc did away with weights and springs in 1983 when they adopted Thunderbolt IV. The automotive industry has been using electronic ignition and advance control for a lot longer than that.

The real question is $300. Do YOU consider it worth $300 for better reliability?

Chris.......
 

Mike Mas

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Just so I'm clear I'm not using a conversion kit ...I'm replacing the whole dissys w the new Pretronix Dist
 

achris

More fish than mountain goat
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Just read the write-up on the Pertronix marine billet distributor. It uses a mechanical advance, with springs and weights.
 

fishrdan

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Looks like the DUI has a mechanical advance also. Toss-up which to choose as they both have their pros and cons. Pertronix is cheaper from a more established company, but you are tied to their proprietary parts. (if they don't use commonly available maintenance parts). DUI is more of a mom-pop shop that can most likely make a better distributor for your application, and with parts that should be easy to locate when needed.

I was perusing flEbay the other day and stumbled across NOS Ford Prestolite marine distributors, and wondered to myself, who in the heck would need a Ford 351 reverse rotation marine distributor.....

http://www.ebay.com/itm/NOS-Ford-35...ash=item5d5e0f0748:g:NvUAAOSw5VFWHH1-&vxp=mtr

And then there was the other side too....

http://www.ebay.com/itm/NOS-Ford-Pr...ash=item4d39b169f1:g:G1MAAOSwl9BWHH1m&vxp=mtr

Of course you can't trust the internet and would need to verify that those are the correct distributors, and would also need to buy the electronic ignition modules, cap, rotor, coil.
 

Mike Mas

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Aug 22, 2016
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You are correct the DUI is a mechanical advance w weights and springs.....also I'm calling them today to confirm that their marine version is Sae j1171 certified
 

Mike Mas

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Aug 22, 2016
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Regarding the prestolite , my two that were original disappeared in transit from NJ to SC as what I was orginally going to do was a conversion kit and new coils... But having to buy new dist anyway has lead me down this path of what to buy ....been quite the education on a couple of forums lol....I will be an expert when it's all over!
Thanks
Mike Mas
 

Mike Mas

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Aug 22, 2016
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Ok so here's an update....the marine DUI dissys is a mechanical advance w weights and springs that DUI sets at the factory based on info you provide... They are geared towards a proformance motor...also they are Marine spec ...but are not SAE J1171 certified therefore if a coastie were to inspect the vessel they could have an issue as this is a noninspected charter ..6 pack boat...from DUI directly they have not gone to the expense of getting them approved but they are up to spec...bottom line as a captain and if there was a fire I wouldn't want to fight with an insurance company

Problem solved going with the Pertronix DIssys ...not enough gain in performance on this application to warrant the expense ...plus lack of CG cert swings the vote against the DUI unit

Thanks for all your input

Mike Mas
 
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