Spark Plugs...Mine HO, 285 HP,  Carbureted (GT40 Heads)  calls for the WL764s.  I have seed both the standard, copper, and platinum electrode versions....I am still running the factory original plugs, but I want a spare set...just in case.  What brand and electrode are you running out there!

Thanks in advance!

Otto

A copper plug typically has a nickel center electrode with a small diameter copper wire buried  in the middle of the center electrode

You can't visually look at any spark plug and see any copper. (unless you destroy the plug to get at look at it)

And like mentioned earlier, the copper core standard plug will be just fine in your engine Otto

And Otto..... you should probably change those plugs a little more often than every 27 years or so.  

Full Threads vs. Half Threads

The thread length shouldn't affect anything. I believe that you are thinking about the plug's heat rating.  Per the Autolite catalog, both the 764 and 104 plugs have a heat rating of  9.

I ran both the 764 and 104 in my 1994 and 2001 boats -- both with the High Performance Ford 351W.  Just for giggles, I change spark plugs every couple of years.  My OCD lizard brain...

Anyway, I would pull the plugs and they both looked and performed the same.

JQ

XP = Iridium

AI = Ultra Iridium

AP = Platinum

APP = Double Platinum 

JQ

Jonny didn't exactly answer this question for you

If you had an AR764 for example, that's an Autolite rrrrrracing plug. You dion't need any of those.

You won't find a plug with WL764 stamped on it anywhere......but if you look at White Lake Marine's nautiqueparts.com you'll see them selling a plug with their part number of WL 764. It's the same Autolite 764 that you can buy anywhere else. No difference in the plug itself....none at all. 

A regular ol' copper core 764 has no prefix in front of it. It just says Autolite 764 on the plug

So if you had a WL764 in your hand and read the stamping it would say Autolite 764

There's plenty of mumbo jumbo out there from all the spark plug outfits to keep you confused  

They both do basically the same thing and minimize RFI

I suppose different brands might do things differently, but as a general rule, they're a separate resistor that's cast or inserted into the insulator

Platinum plugs were the first long lasting plugs offered, they came about to handle the high energy ignition systems first introduced int he 90’s.   First single platinum and then double platinum plugs came out.  They can last 100,000 miles in cars but the negative is it takes more energy to fire a platinum plug so they only work well in high energy systems.

Iridium plugs are fantastic plugs, they can last well over 200,000 miles in car applications.  They fire with less energy than the platinums so that is another plus.  They use fine wire technology which gives a more focused spark, all good.  These are basically lifetime spark plugs.  The only negative is they still need more energy to spark than a standard copper plug.   

So you are out on the water, been relaxing listening to your tunes, time to start your boat and head home.  The battery is low so the engine cranks slowly.   The best plug in this case is the cheap standard copper plug.

In a standard ignition system (not high energy ) the copper works best as it will make a spark in the lowest energy situations and maybe get you started.

IF copper plugs are used in a high energy system they will wear fast because the high energy spark will blow particles off the electrodes as the engine runs and slowly open up the gap of the spark plug,   They would still last 5,000 miles or more in a car.   In a boat that is probably a couple hundred hours at least.

In a 1995 or newer boat I would consider Iridium plugs as a never change again option.   In boats with points in the distributor ignition systems I would stick with the std copper plug options.

I am not a fan of the platinum or double platinum plugs due to the high energy required to fire them but they came in millions of cars and did outlast copper.

Here's a link below with input from the Director of Engineering at Autolite that doesn't exactly agree with what was written above about what type plugs fire easier.

And keep in mind that what's commonly called a copper plug has a copper core inside the center nickel electrode. A platinum plug has a platinum tip on the center electrode. The electrode is still nickel with copper in the middle.

Double platinum has platinum on the tip of the ground electrode too

Iridium same copper core surrounded by nickel with really fine iridium tips

But we probably all agree that in this thread about a 351w with gt40 heads, the normal nickel electrode with copper core works just fine and platinum or iridium will work just fine for longer and depending what you buy, can be pretty pricey.

Sometimes old myths die hard, kinda like synthetic oil being too slippery

http://www.championautoparts.com/Parts-Matter/automotive-repair-and-maintenance/Spark-Plug-Materials.html" rel="nofollow - link

And an NGK link below

http://www.ngk.com/learning-center/116-plug-anatomy" rel="nofollow - link

The almost dead horse was just heard muttering................. "why don't we all start talking about plug wires now?" just so there can be more disagreement and opinions