Multiple electrode spark plugs

They were a scam then and they're still a scam.

Tony

Is that CDI system causing the stock plugs to burn out faster? If not keep the stock plugs!

Some of the watercooled engines will burn out their stock spark plugs within a 6 month period but not the long-life plugs. I DON'T buy those "aftermarket" Bosch Platinum 2 or 4 electrode plugs unless recommended by VW. And usually the correct Long-Life plugs can not be purchased at your FLAPS. Remember here we are talking a FI-ed engine trying to run at very lean conditions. Your air-cooled engine is probably not running as lean. ;-) JMHO

Only those who are interested in long-term reliability.

No matter how many ground-electrodes the plug has, the spark only jumps to ONE of them. Which is good.

Spark plug electrodes erode away in normal use, causing the gap to become wider.

With multi-electrode plugs the spark jumps first to one, then to another, effectively DISTRIBUTING the normal erosion.

The net result (and the reason for multiple electrodes) is to EXTEND the normal service life of the spark plug, which is why multiple electrode plugs have been standard items in aircraft engines, industrial engines and so on, for more than seventy years.

But if you expect to screw in a set of such plugs and see some miraculous increase in power -- as did Gene Berg -- you can forget about it; that's not what they're for, although that is how they are advertised to the Kiddie Trade. More is always better, right? :-)

So what's the 'platinum' deal?

Since ALL of the electrodes erode in use, the traditional design used a large center electrode surrounded by three or four ground electrodes in the form of a segmented cylinder. This was because the single center electrode eroded at a faster rate than the multiple ground electrodes. Because of the design, such plugs tended to foul at low speed and were difficult to clean and gap. The modern 'platinum' center electrode (it's actually a platinum-tungsten alloy) has a slower rate of erosion, allowing you to use a smaller center electrode

-- in some designs a mere dot of alloy -- making it much more resistant to fouling, easier to clean when it did, and may be accurately gapped without using special tools.

-Bob Hoover

All this talk about extended plug life is more or less irrelevant for us aircooled VW heads, because our plugs actually SHOULD come OUT more frequently than plugs in modern cars. It's because they get dirty with carbon buildup, resulting from less optimal burn process than what you'd see in a computer controlled EFI engine of today. The plug threads get their share of slow buildup, and when you finally pull the plugs out, you strip parts of the threads in the head out too. Repeat a couple of times, and the head won't hold the plug at all anymore.

Use whatever plugs you like with the correct heat range and piston clearance, but change them as frequently as you would change old skool plugs. You can spend the money on fancy 100.000mile plugs, but you won't get your money's worth when you change them at 20k.

As stated before, there is NO performance gain. A spark is a spark.

Jan

Well I will agree with you about staying with stock plugs, but IF there are other modifications to the fuel delivery system to run very lean, AND to the ign system boosting its power that might cause the normal stock plugs to burn out quickly. Then maybe the OP can benefit from extended life spark plugs. Is the OP complaining about plugs that are "burning up"?

I agree about removing and installing spark plugs on a regular schedule. I have seen some that did not want to come out damaging the cylinder head.

AFAIK the first Porsche 911 engines preferred Platinum Spark Plugs to run better. These plugs could still foul out though but there was a noticeable power increase.

No. I thought that since the plug gap is supposed to be opened up from .028 to at least .040 for the CDI the multi-ground plugs would bridge the gap better than the W7AC plugs I normally use. After all, the platinums cost about 3 times as much so they must be good for something, right? :-)

I always coat the threads with anti-seize lubricant like my Bentley manual says. I've never had a problem with galling since I went with the anti-seize. Unfortunately, its use won't prevent you from cross threading -- if you're not careful.

Bob Hoover wrote in his Sermons, "With a dependable 40,000 volt spark at all engine speeds the spark plugs may be gapped much wider, providing better flame-front ignition. The wider plug gap fouls less readily, giving even worn engines a boost in efficiency.... Over all, CD ignition insures better combustion, resulting in better fuel efficiency and lower emissions. The engine even runs cooler, thanks to less after-burning in the exhaust manifolds."

Unlike you and Jan, I have concluded that I can examine the plugs less often because they don't foul and don't show evidence of carbon soot build up, probably due to the high voltage spark at all speeds.

Wrong Jan, think CDI and try again, a weak spark will "blow out" as in opposite to a really fat multiple one, which will trigger like a licked

J.

We are not talking about those snake oil fraud things like the Predatator or Split Fire. Right?

Well, the new multi (4) electrode plugs have one special advantage - their radial layout does not obscure the spark from the mixture as typical plugs do (and the Split Fires obscured the spark even more than stock plugs!)

No,no. Multiple sparks from the cdi unit below 3000rpm or there abouts. Sorry, I was unclear on that one.

Multiple ground electrodes shields the travel of the flamefront, not good.

J.

Maybe I need a friggin illustration, but I don't see how the four-point plugs can obscure the mixture like those POS Splitfires and stock plugs do.

Most of the travel is done on the horizontal plane, piston is on top...

J.

The flame front needs to travel in all directions from the center of the plug. On regular plugs, one direction is obscured by the side electrode. On 4-point plugs, FOUR directions are obscured by side electrodes. On all-out racing engines, you index the plugs so that the side electrode is located in the least important side of the combustion chamber. (Draw a line on the side of the plug insulator right where the side electrode is and you'll know where it is, when tightening the plugs down)

You can get plugs with NO side elctrodes, if you really want an unobstructed path...:)

There is no need for multiple electrode plugs in an aircooled beetle engine. The design itself gives you no benefit. The materials used is where the benefit comes from, they'd have the same benefit with just one side electrode. (Center electrode resistance to wear).

Addition of a CDI ignition module will of course help produce a bigger, fatter spark. But you'd need to widen the plug electrode gap to allow it to happen. It works with any type of plug, so 4 electrode design again is not necessary. In fact, the gap on most of them should never be adjusted, according to the instructions. (I use Bosch platinum/iridium 4 points in one of our daily drivers).

Jan