After seeing the new Hemi 5.7 at the IAS, I noticed that it each of its 8 coil fires the plug beneath it, and a plug on the other cylinder bank.

Assuming one of the coils fails (it sometimes happens), that cylinder will still fire, via a coil on the other bank. If a plug shorts (it also happens), that cylinder will still fire, as there are two separate coils AND plugs for each cylinder.

This sounds like a good thing to me, and worth the extra cost of the 16 plugs. Theres no point in designing a engine to produce over 300hp, just to lose it due to a weak ignition system (Optispark comes to mind).


With an LS1, for example, if a coil or plug fails, you lose that cylinder.

With a 4.6 Ford, if a coil or plug fails, you lose 2 cylinders (only 4 coils)

The Gm 3.8 uses 3 coils per 6 cylinders, so again lose a coil or plug, you lose 2 cylinders.

Doesn't the new GenIV use dual plugs? Maybe they'll also use this coil approach.

 

Yeah that’s a really cool design. I thought it was over done until I lost two coils on a road trip at the same time. How my 3.4L drove on 2 cylinders for 20 miles to we finally got to a Chevy dealership I don’t know. But thank god it did. Gm and Ford should defiantly look into this.

 

If a coil fails, then you just replace it. It is real easy to do in cars with the 3800 V6. If a coil in the Hemi dies, it will still run like ****, just like any other engine.

 

Now that I think of it, this is similar to basic aircraft technology. Two independant ignition systems.

Ignition fails on a car, it's a nusance. Ignition fails on a small plane, it might be fatal.

 

Aside from Star's incident, ignition failures really are quite rare nowadays. Like any design decision you need to weigh the cost versus the risk or benefit, and if they did this solely for redundancy I doubt it would be worth it.

Perhaps the real reason is that it would take a lot more power for one coil to fire two plugs simulaneously, so this way they can use two coils for each cylinder without doubling the coil count.

 

You don't get it. Each cylinder on the Hemi is fired by TWO independant coils. BOTH of those coils would need to fail for the cylinder to miss.

 

Each coil IS firing two plugs simultaneosly, otherwise only one plug per cylinder would be fired during the power stroke, the other would be waste spark during exhaust stroke. They woudn't design in 16 plugs just to provide a waste spark. One coil/cylinder can easily handle a waste spark.

 

FYI....99+ 4.6's have coil-on plug.....ie...8 coils.

 

No, I get it, I know how the Hemi is set up. I would think that if 1 coil dies it will still run crappy since that one cyl. isn't getting enough spark. Granted it won't be as bad as if a coil that is controling 2 cyls dies.

The New Hemi is a kick *** engine

 

You wouldn't even notice the difference if one coil failed on the Hemi. The extra plug helps combustion and emmisions mainly during part load and Idle. It'll thow a code, then you'll really know. If an LS1 lost a coil, you'd know immediatly.

I owned a Mazda Rotary with dual ignition. It ran fine on either (yes, I actually tried). A friend had a Nissan with the NAP-Z engine that used 2 plgs per cylinder - it also ran fine on one plug/cylinder.

Now, WHEN are they putting the new Hemi in a car?

 

Wow, that is good to know. Is there any/much performance gain to going duel plugs? I assumed Dodge did it for emissions reasons.

The Hemi goes into the 300C and Dodge Magnum this comming spring.

 

Apparently, the basic Hemi design is bad for emmisions. Adding the extra plug addresses mainly this, along with some idle quality and part-load performance. Even with the 2 plugs, it still doesn't meet ULEV status. Considering this is an all new design, it should.

I would estimate that the extra plug might provide no more than 5% more Hp, under certain conditions. Otherwise GM and Ford would have jumped on the dual-plug bandwagon long ago.

Lose one coil or plug on a LS1, and there goes 12.5% of your Hp, guaranteed. Lose a coil on a Hemi, and you might lose 5%. Maybe. The only thing I don't like are all the plug wires running across the engine and manifold.

Do a Google search on "5.7 hemi dual plug" and there are some good articles on what exactly the dual plugs do.

 

I remember a couple of buddies back in the 80's had Nissan trucks that had 2 plugs per cylinder.

 

Yup. Using two plugs per cylinder had almost nothing to do with possible coil failure (a rarity these days). DCX engineers couldn't get an efficient burn with just 1 plug. No sir, I wouldn't give them too much credit for this one.

 

Just because and engine doesnt burn cleanly with just one plug doesnt make it a bad design. Mercedes makes has a few very nice engines running multiple plugs per cylinder which are much more "refined" and expensive than the Hemi.