Side Gapped Spark Plugs - Is Everyone This Obsessive?

[Gordo2]

My spark plugs were due for a change, which provides a recurring opportunity to obsess over minutia.

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My non-stock 3.2L
Dougherty Racing GT2-102 cams (Dougherty Racing Cams)
JE 9.5:1 pistons (measured static CR 9.3:1)
Electromotive XDi Ignition
SSI exchangers with M&K 2-2 muffler
Stock 3.2L heads - reconditioned
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As I was researching the optimal spark plug gap for my PMO carb and XDi combo (manuals simply don't satiate curiosity), I came across a old idea but new obsession - Side Gapped Spark Plugs.

With Dremel in hand - a few minutes later my new NGK BPR5ES were side gapped to 0.045" (previous BPR6ES @ 0.035" were somewhat sooty - but mixture was stinky rich). Side gapping involves cutting off a small part of the ground extension to uncover the center electrode - in concept, exposing more of the spark to the fuel mixture.

(Left plug side-gapped, right plug unmodified)


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For the obsessive types (go-ahead... own up), here's one more tangent & option to consider the next time you change your spark plugs, and an article to start you down the rabbit hole: Performance Unlimited - Side Gapped Spark Plugs Article

Driving impressions: I'm confident I could feel the ~1HP increase this modification provided

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It could end here - but I also stumbled across the idea of spark plug indexing, but I'll save that for another time, another tangent...

Enjoy

[Hi_Fi_Guy]

A few corvair racers I know swear by plug indexing.

[manbridge 74]

Hemi shaped chambers are lazy burning. Anything to better present the spark will help prevent detonation and while minimal, a slightly better burn. 930 and early MFI 911S (1969!) plugs were also side gapped.
Obsessing would be smoothly chamfering the edges left from your cutting...

[proporsche]

good idea , make sense,i will do this next week and search for the 1 horse;-)

Ivan

[Gordo2]

Originally Posted by manbridge 74

Obsessing would be smoothly chamfering the edges left from your cutting...

Considered chamfering (I'm obsessed right...) - but the linked article suggests that it's better to leave the cut edges sharp, but de-burred:

"The sharper edges also encourages the spark to ignite quicker and stronger, much like striking an arc with a welder on an edge rather than a flat surface."

Originally Posted by Hi_Fi_Guy

A few corvair racers I know swear by plug indexing.

Now you're just goading me : )

[Discseven]

Fine idea Don!

[manbridge 74]

Sharp edges are also prone to cause premature ignition, consider a colder heat range...

[ClickClickBoom]

The $64,000,000 question. If this was a "thing" why doesn't the spark plug manufacturer do this?
Is this a "cool collar" mod in search its next victim. Look up preignition.

[Canada Kev]

The manufacturer probably won't do this because the plugs will wear a little bit quicker and asymmetrically because the arc will be primarily jumping from just the one side of the electrode and not the middle like normal causing a shorter life. Perhaps not worth it to them for a small amount of power increase.

[tirwin]

Originally Posted by ClickClickBoom

The $64,000,000 question. If this was a "thing" why doesn't the spark plug manufacturer do this?
Is this a "cool collar" mod in search its next victim. Look up preignition.

Well there was a company that did this called Splitfire (referenced in the linked article).

Wikipedia says the company is now defunct. It seems the FTC took issues with their claims and it hurt sales. Maybe the idea is good but they oversold it. Or it’s hokum.

The idea is interesting. The assumption is that it creates a better flame front. But how would the claim be proven?

What is the risk? No difference? Weaker spark/poorer fuel burn? Detonation? Detonation would be bad. Even worse on a car with no knock sensor.

[manbridge 74]

The negative is losing the ability to regap. This is why the OE side gapped plugs had noble metals on either side of spark.

[rsscotty]

These are the OEM spark plugs for the 3.6 twin plug engines. Don't know what would be better for a street car.

[Trackrash]

Cool. I'm waiting for dyno and emission comparisons.

Why not ask this in the engine rebuilding forum?

[manbridge 74]

Three prong side gap lasts three times as long. Again, presenting the spark with no obstruction to get a faster flame front going. It’s not so much an explosion but rather a burn spreading out from the spark.

[patkeefe]

So, is the orientation of the ground electrode the same for each plug, ie, does it point toward, say, the intake valve, or did the factory randomly cut threads into the plug holes so that there is in infinite arrangement of orientations? And, does the 3.6 plug pictured above increase the possibility of the electrode being in an optimal position for igniting the mixture? Does the orientation of the plug matter at all?

[fanaudical]

Not meaning to highjack the thread, but does anybody think that retrofitting the three-electrode plugs to older motors (like a near-stock 2.7) is worthwhile for any reason?

Incidentally, all my Audi's (both 2 and 5 valve motors) came equipped with those three-electrode plugs. Never had any issues and they lasted a long time. Gapping took some time, though...

I've read some stuff that is not in favor of multi-ground-electrode spark plugs like these for high-rev motors - something about the multiple electrodes sometimes obscures the spark from the air-fuel charge.

Not quite related to the comment above, but here's a link to some info presented by NGK. They might have factory single electrode side gapped plugs available:

https://www.ngk.com/learning-center/article/772/ngk-ground-electrode-designs

[Trackrash]

Originally Posted by patkeefe

So, is the orientation of the ground electrode the same for each plug, ie, does it point toward, say, the intake valve, or did the factory randomly cut threads into the plug holes so that there is in infinite arrangement of orientations? And, does the 3.6 plug pictured above increase the possibility of the electrode being in an optimal position for igniting the mixture? Does the orientation of the plug matter at all?

Hard core racers have been known to "index" the orientation of the plug's ground. Apparently it makes a difference on some motors.

[Gordo2]

A few additional thoughts and responses:

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Originally Posted by Trackrash

Cool. I'm waiting for dyno and emission comparisons.
Why not ask this in the engine rebuilding forum?

Sorry Trackrash - my vehicle is emissions exempt, and I have bigger fish to fry next time I hit a dyno (been meaning to hit a load dyno to adjust XDi total advance for max torque).

The Engine Forum would have been less entertaining with JW, Steve W and other pro's quickly ending the discussion with experienced observations - anticipated responses: BTDT - limited juice vs. squeeze / just buy a set of plugs with exposed tip if that's what you are shooting for (there are off the shelf options - but more $$).

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Originally Posted by manbridge 74

The negative is losing the ability to regap. This is why the OE side gapped plugs had noble metals on either side of spark.

Appears you, Canada Kev and I are on the same page as to why standard plugs aren't side gapped - you expect longer / extended life out of more expensive plugs.

My NGK's cost ~ $2.50 per, and at that price I will change them on a whim (my last set only had ~ 10k miles). If I decide side gapping was a bad idea - oh well, I'll get a new set for $15.

My newer vehicles all use Iridium plugs @ ~ $10 per plug. Newer vehicles have very efficient engine management systems that enable precise mixture, temps & active knock control - which combined with plugs that use very durable materials ($$) contributes to longer plug life & consistent, reliable performance.

I changed the original Iridium plugs on my 2005 Toyota 4Runner last year @ 120k miles - the old plugs looked like new, and the gap was still good / in spec. No hesitation to spend $80 on a new set of plugs that I expect to last the next 14 years / 120k miles. If I were changing the plugs every 10k miles or so - I would be looking for a less expensive set.

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Originally Posted by patkeefe

...is the orientation of the ground electrode the same for each plug... And, does the 3.6 plug pictured above increase the possibility of the electrode being in an optimal position for igniting the mixture? Does the orientation of the plug matter at all?

Orientation of the ground is not consistent due to thread variations - from plug to plug and head to head. As such, indexing appears to take some time to achieve the desired orientation.

Orientation seems to matter to those who think so . Meanwhile the concept seems sound, and my expectations are reasonable (i.e. I don't anticipate any perceivable performance improvement by indexing).

On the other hand, if combined with a detailed tune up resulting in a perfect smooth idle, tune and performance - I would be inclined to believe that indexing contributed to the overall endstate...

I assume the 3.6 plug is designed with the intent to optimize spark exposure.

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Originally Posted by manbridge 74

Sharp edges are also prone to cause premature ignition, consider a colder heat range...

True / good thought - the sharp edged plug grounds definitely goes against my efforts & obsession elsewhere within the combustion chamber (like filing the sharp edges off the tops of my JE pistons...).

Although I have 9:5 pistons, which should be fine running with regular / ~ 87 octane fuel, I always run 93 octane. I like to think it provides me some safety margin to play with the XDi advance settings, and some margin to toy with side gapped, hotter plugs (higher octane has a higher flash point / less likely to ignite on a hot spot).

In spite of my best efforts, I've found my carb'd engine performs best with the carbs set slightly rich - and with my frequent, relatively short drives, my plugs have tended to be dark - hence the swap from the 6's to the hotter 5's. Will check them soon.

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Thanks for the comments and thoughts folks. Always fun, and I'm always receptive to to new ideas, thoughts and the discussion - it's what keeps me obsessed with this forum.

Gordo

[tobluforu]

Originally Posted by rsscotty

These are the OEM spark plugs for the 3.6 twin plug engines. Don't know what would be better for a street car.

I ran this plug style years ago in my 72 mfi until they stopped making them, at least I could not find them any longer. Best darn plug ever run in that gas gobbling engine.

[Quickstep192]

This is interesting stuff.

I found the attached article from Autolite about multi ground side gapped plugs. The article talks about why they weren’t all they were cracked up to be because the spark can only jump between one of the grounds at a time and the other grounds are basically in the way. Even so, they are truly side gapped and present no obstruction to the spark.

Why wouldn’t a manufacturer make a single ground, side gapped plug for performance based cars?


In the Autolite article, they go on to talk about their iridium plugs, but it seems the iridium plug still has the ground obstructing the spark.


https://www.autolite.com/docs/default-source/tech-specs/understanding-spark-plugs/understanding-mge-spark-plugs-2017.pdf