Anyone tried only 8 plugs on a high compression race application?

[RockinRobin]

I've raced my Hemi swapped Duster for 11 years now, but I've always wondered if I would lose anything by running just 1 spark plug per cylinder, since the 2nd one is only there for emissions and this is a race only car.
Has anybody tried this??
thanks!

 

[TT5.9mag]

Sounds like you need to be the test mule.

 

[ch1ll]

I'm old enough to remember when top fuel went from one to two per cylinder. You must have a gen 3 hemi. In a gen 1 or gen 2 hemi 2 is always better than one.

 

[George Jets]

Good hot e-core coils and plugs gapped at 55 ths.

Only need one spark plug to set off the charge.

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[A56]

 

[RockinRobin]

Good hot e-core coils and plugs gapped at 55 ths.

Only need one spark plug to set off the charge.

View attachment 1716478492



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How do you block off the 2nd plug hole in each cylinder?

 

[RockinRobin]

I'm old enough to remember when top fuel went from one to two per cylinder. You must have a gen 3 hemi. In a gen 1 or gen 2 hemi 2 is always better than one.

I'm sorry. I thought I posted this in the Gen3 Hemi Swaps Forum. Yes, I have a Gen3 Hemi.

 

[RockinRobin]

Sounds like you need to be the test mule.

Possibly. At my compression ratio, plugs are $11 a piece. If I can cut that in half without losing performance I'm game!

 

[DionR]

I'm sorry. I thought I posted this in the Gen3 Hemi Swaps Forum. Yes, I have a Gen3 Hemi.

I've been tripped up before when I look at "new posts" and miss that a thread was posted in a certain forum. Last time it was a drag racing forum and I missed that and responded in ways that didn't apply.

 

[A56]

How do you block off the 2nd plug hole in each cylinder?

Couldn't you just use another spark plug?

 

[DionR]

How do you block off the 2nd plug hole in each cylinder?

What if you just left an old spark plug in the hole?

 

[DionR]

Kind of feels like you could test this by just stop replacing one of the plugs in each cylinder. Let that one hang out and if it fires or doesn't fire, who cares. See if you start losing some performance. Maybe give it a decent amount of time and then swap to all new plugs and see if you pick up any time.

 

[MadScientistMat]

It's not just emissions; two plugs mean a much faster burn and less time between ignition and peak cylinder pressure. I have not seen one dynoed on one plug per cylinder but I would expect the engine to lose power.

 

[George Jets]

You have a Waste Spark ignition on that gen III.

Both plugs are not firing at the same time in each cylinder. They are firing the one under the coil pack on compression, the other plug that is firing on the exhaust stroke on the opposite paired cylinder. Hence the name "Waste Spark Ignition".

Leaving all 16 plugs in, but eliminate the lead to the 2nd non-coiled plug.

You may even get more performance out of it as you are not heating up the e-coil to fire 2 plugs at the same time.

Just thinking out loud here, you are going to have to do your own research on running 1 plug instead of 2 on your gen III hemi.

A simple plastic insulator on the coil pack end of the unwanted spark plug would keep that plug from firing when you bolt in the 2 lead coil pack.

CAUTION: Knowing these computer controlled engines, I don't think it is going to like to fire only 8 plugs vs the 16 it came with. Sensors will talk back to the computer and possibly throw the system into "Closed Loop" mode as it is sensing something wrong?? Then there goes your performance out the window.

These racing situations you will have to figure out on your own, don't want to damage that nice engine.


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[fishmens67]

It's not just emissions; two plugs mean a much faster burn and less time between ignition and peak cylinder pressure. I have not seen one dynoed on one plug per cylinder but I would expect the engine to lose power.

I think you just answered the op's question, if anything the 2 plugs are an advantage for a race engine.

 

[DionR]

You have a Waste Spark ignition on that gen III.

Both plugs are not firing at the same time in each cylinder. They are firing the one under the coil pack on compression, the other plug that is firing on the exhaust stroke on the opposite paired cylinder. Hence the name "Waste Spark Ignition".

Leaving all 16 plugs in, but eliminate the lead to the 2nd non-coiled plug.

This only applies to the '03-05 5.7 G3. The ones that had a snake nest of ignition wires running over the intake manifold.

All others use the ignition coil you pictured that fire both plugs at the same time.

As far as I can remember, the '03-05 5.7 can run the later valve covers and coils without causing PCM codes or anything. I don't know if there was a performance advantage, but I know it cleaned up the motor significantly so many do it for that reason alone.

But, your post does point out that at the inception of the G3, the factory was running the motor on a single plug. So it might work.

My gut says a single plug will be worse than the dual plug, but it's just a guess.

 

[George Jets]

Here is a pretty good shorter video of picking up 20 more horse power on the low end and 7 hp on the high end, just by changing the coil packs from OEM to Aftermarket Performance coil packs.

Dyno tested results and used the same spark plugs.



Makes sense run a hotter spark, and burn more fuel.


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[remytherat]

I think you would lose a small amount of power. The emissions reason is that you get a more complete burn with two as opposed to one. More complete burn also means more energy is extracted from a given amount of fuel, so more power for a given amount of fuel injected.

That said, I think that the difference would not be measurable.

 

[TT5.9mag]

Possibly. At my compression ratio, plugs are $11 a piece. If I can cut that in half without losing performance I'm game!

At your compression ratio (cylinder pressure) and fuel load, you don’t need two plugs per cylinder to complete the burn or “speed up the burn”. Thats all horse crap. If you were on alcohol and 30psi of boost you might see a difference with two plugs because the chance of blowing one out is higher. It will make almost no difference in power with one vs two.
If you walk in to a room full of gasoline vapors with a lit match what happens?
If you walk in to a room full of gasoline vapors with two lit matches what happens?

 

[TT5.9mag]

Here is a pretty good shorter video of picking up 20 more horse power on the low end and 7 hp on the high end, just by changing the coil packs from OEM to Aftermarket Performance coil packs.

Dyno tested results and used the same spark plugs.



Makes sense run a hotter spark, and burn more fuel.


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Nope. That guy is full of ****. He says “more capacitive discharge” from a coil that has no capacitors in it. I looked at some of their dyno testing and controlling finite variables is not part of their testing protocol. Take the information in those videos with a very large grain of salt.

 

[junkyardhero]

Here is a pretty good shorter video of picking up 20 more horse power on the low end and 7 hp on the high end, just by changing the coil packs from OEM to Aftermarket Performance coil packs.

Dyno tested results and used the same spark plugs.



Makes sense run a hotter spark, and burn more fuel.


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i wonder how far the computer retards the timing for those super hot coils...

*eyes roll into back of skull*

 

[TT5.9mag]

i wonder how far the computer retards the timing for those super hot coils...

*eyes roll into back of skull*

Well there’s 16 coils so 16 times more retard.

 

[remytherat]

“more capacitive discharge”

Lol yeah, dude has absolutely no idea how an ignition system works.


Crazy to think he does this professionally

 

[TT5.9mag]

Lol yeah, dude has absolutely no idea how an ignition system works.


Crazy to think he does this professionally

What’s even crazier is people buy his garbage

 

[Newbomb Turk]

At your compression ratio (cylinder pressure) and fuel load, you don’t need two plugs per cylinder to complete the burn or “speed up the burn”. Thats all horse crap. If you were on alcohol and 30psi of boost you might see a difference with two plugs because the chance of blowing one out is higher. It will make almost no difference in power with one vs two.
If you walk in to a room full of gasoline vapors with a lit match what happens?
If you walk in to a room full of gasoline vapors with two lit matches what happens?

Any time you can delay spark timing and not lose power you gain power from less negative work.

Any NA engine should be built doing everything that can be done should be done to speed up the burn rate.

That’s higher compression, tighter quench and any modification to the heads and intake manifold that at least helps to atomize the fuel.

All that ends up with less timing and NA that’s a good thing.