Sidegapping plugs

[billyboy]

http://www.performanceunlimited.com/documents/plugsidegapping.html

[Pazuzu]

It's notable that he makes no mention of then INDEXING the plugs in the heads, which is pretty much required for sidegapped plugs.

Indexing is when you aim the sparkfront towards the center of the combustion chamber by making sure that the plug is indexed when tight in the head. You need to use copper indexing washers to do this.

[dshepp806]

Mike,...how is done? (with the indexing washers, etc.....I've never done it...)

Thanks,

Doyle

[cashflyer]

One of the reasons the spark plug has such a large ground electrode is for long plug life. Most consumers want to install it and forget about it for a long time. I know some car salesmen tout certain brands as not needing a tuneup for 100k miles.

Because the arcing action erodes the electrodes, a plug modified as shown on that web page will have a significantly shorter life span. This is not a problem for racers and others who constantly tinker with their car, but I doubt that it's an advisable mod for somebody who uses their car as a DD or weekend wax-whore.

[kucharskimb]

A note on the washer indexing....

I found it very difficult with the orientation of the plugs and the subsequent removal of them to keep the washers from falling into the head/cylinder fins... eventually, i just gave up using the washers.

[Pazuzu]

Oh, there's no DOUBT that indexing plugs is hard enough, and with the deep Porsche access, it would probably be nearly impossible to do consistently. I figure that liberal use of copper antisieze might help hold them in place...

Basically, to index your plugs, you need to mark them in some way that you can tell which way the electrode is directed when it's mounted in the head...maybe a black Sharpie mark on the ceramic. You install the plug to torque, then (somehow) get a look at it and see if the electrode is pointed correctly, based on your mark. If not, you remove the plug, and add indexing washers so that when you put the plug back in, it hits torque *earlier* in it's rotation. you keep changing washers until you get the mark showing that your electrode is pointed towards the center of the combustion chamber.

It's about 1000 times easier in any other engine...but hey, who among us bought a Porsche for EASY engine work?

[Quicksilver]

If you are looking for the last fraction of a percent of power (like a drag racer) then this is still of questionable value. It might fractionally (REALLY fractionally) reduce the time required for combustion which would let you run closer to the ragged edge of detonation which might let you get a small percentage of a horsepower that might make a difference in a 1/4 mile... As was mentioned before, indexing will get you a bit of power. (By making the flame propagation consistent across all the cylinders.) You won't be able to get it to show up on a dyno though.

The fact is that more people spend (waste) more time and money doing voodoo on ignition systems then almost any other thing on a car. The truth is that you can't get the fuel air mixture to be "more burnt". Either it lit off or it didn't. There is no half way! I dare someone to try and explain how the air/fuel mixture only burnt halfway. So you think your special plugs/coil/wires made it light of a fraction of a second quicker? Ok... How is that different then advancing the timing a half degree?

The fact is you just want it to light off consistently every time. Good wires, and good clean plugs will do that. Making the plugs spark more times or having wires with capacitors (Nology) in them is similar to waving a dead chicken over the engine.

Replacing the points with a reliable electronic (non degrading) trigger will get you something. Trimming the plugs that were already lighting off the fuel will only limit the life of a plug.

[Flieger]

Can't you just use some Bosch +2s that have an unshrouded ground electrode with the 2 cathodes on the sides? This would allow good flame propagation without the trimming of factory plug electrodes.

[afterburn 549]

No magic there, 2 stroke plugs come that way. ( At last count) To index or not ..like said old race trick..would like to see a dyno sheet of B4 and after. Esp on a low C/R eng.

[Pazuzu]

I wouldn't index a full electrode plug, but if you hack away that electrode, I'd sure as **** want to know that the effort put it was going to go towards firing the spark into the gas...otherwise, why go through the effort of cutting the electrode down?


Or, we all switch to the side firing, 4 ground electrode plugs that were in my old RX-7...weird things they were...

[dshepp806]

Thanks for the explanation, Mike.

My best,

Doyle

[cashflyer]

Originally Posted by Quicksilver

The fact is that more people spend (waste) more time and money doing voodoo on ignition systems then almost any other thing on a car. The truth is that you can't get the fuel air mixture to be "more burnt". Either it lit off or it didn't. There is no half way! I dare someone to try and explain how the air/fuel mixture only burnt halfway. So you think your special plugs/coil/wires made it light of a fraction of a second quicker? Ok... How is that different then advancing the timing a half degree?

While I am not going to hype up the advantages of indexing your plugs, I will say that the reason people do these type things is not because they believe that the AF mix isn't burning completely. It's because they believe it's not burning completely fast enough.

A couple of quick facts:
1) As compression and heat increase, so does the resistance of the spark to jump the gap between the electrodes.

This is the primary reason for installing hotter coils and hotter ignition systems.


2) The time allotted for the AF mix to burn is infinitesimally small. Think of an engine running at 6,000 rpm. That means the piston makes one complete cycle every 1/100th of a second. The ignition event begins 5 degrees BTDC, and the burn must be complete before BDC - roughly 5 thousandths of a second later.

This is the primary reason for running dual plugs. Your ignition event is started at two points within the combustion chamber, allowing the flame propagation to be quicker and more even.



So, back to the issue of cutting down a plug. Does it help? I don't know.

In my opinion, I think it would be an amount so small that it would be hard to quantify. While the spark is more exposed, it is still in a single location so flame propagation has not been changed. And the spark gap has not been altered, nor the ignition energy increased, so nothing has been done to allow better operation at high compressions or temps.


YMMV

[RWebb]

"indexing will get you a bit of power.... You won't be able to get it to show up on a dyno though."

- Eh??

Let's look at this another way -- what hp increase will you get with twin-plugs (only). Answer is just about zero, tho it will run smoother/better. (Benefit in hp is that 2 plugs allow more compression, and that allows more power).

So, if 2 actual plugs does nearly nothing for power, what do you think twisting the plug around is going to do?

And, of course, you can also compare the travel time of the SPARK across the spark plug with the travel time of the FLAME FRONT across the cylinder head. Think about it...

[afterburn 549]

I would think time and $$ spent on dual plug would better spent then most any thing else