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Rollin On 4:56's
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Discussion Starter · #1 ·
1- Why is it that our hemi's have two plugs per cylinder rather than one like the other trucks?

2- Someone who I know who works for DCX told me that at a certain point, two of the cylinders in the hemi's shut down at a certain point, is that true or is it bulls**t?

Don't want to sound stupid, I just don't know about this.

Many Thanks
 

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The Hemi features cylinder deactivation in the 300C and Magnum R/T; the "Multi Displacement System" (MDS) turns off the fuel consumption in four cylinders when V-8 power is not needed. This provides a world class combination of performance and fuel economy, without the driver noticing any difference.
Michael E. Gemmel wrote: “Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. It appears that each cylinder shares a coil pack with another cylinder. Each of the two plugs on a given cylinder is fired by a separate coil. One plug has a coil directly attached, and the other is fired via an ignition wire connected to a coil located on another cylinder on the opposite bank. The benefits would be one-half the number of coils (8 vs. 16) compared to each plug having its own coil, and of course less weight.”

“Cryptojoe” wrote: “Being the good Motech Graduate I am, I can say that the extra plug fires during the power stroke in order to more full burn the hydrocarbons. While this does add to NOx (oxides of nitrogen) and ozone emissions, it relieves the catalytic converter from becoming overwhelmed with unburned hydrocarbons. Unlike the Japanese systems of the late 1970s and early 1980s, which avoided the use of catalytic converters, the second ignition allows additional power in the down stroke while lowering the need of restrictive catalyst plates in the converter. This increases breathing, and in turn adds to horsepower output as well.
All taken from:
http://www.allpar.com/mopar/new-mopar-hemi.html
 

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LPG Hemi
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1) I believe the two plugs per cylinder are to get better emissions. Also you only need 8 coils and not 16 which saves weight.
One plug fires on the normal power stroke and the other lead from that cylinder which has just fired, fires a reciprocal plug on the other bank.
2) Yep, some of the new Hemi's (someone on here will post up which ones) have a system called MDS.....Multiple Displacement System.
This turns off 2 culinders at times of low load on the engine, to save gas. Effectively making the V8 a V6.
It's all seemless and aparently transparent to the user. However, I have seen posts on here and other forums where people say they can tell from the engine pitch which it goes over to V6 mode.
There's no stupid questions, only people who are stupid in not asking in the first place.
This link will explain simply, what the MDS system is and about the two plugs per cylinder.
http://www.allpar.com/mopar/new-mopar-hemi.html
Hope this helps you bud?
Al.
 

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Sorry, but “Cryptojoe” was speculating. The original dual-plug design was for redundancy (you could lose one spark plug per cylinder or a total of 4 coils and still run), and for cleaner emissions. The point to remember is that both plugs in each cylinder fire together during the compression stroke as well as the exhaust stroke. The advantage of redundant ignition has been minimized by the MDS feature since the cylinders are now controlled by a single coil each (I assume) so that they may be deactivated when necessary (with MDS if a coil fails, you lose the cylinder).
 

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Rollin On 4:56's
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Discussion Starter · #6 ·
ahhhhh, i new all that, just wanted to see if anyone else knew. :)
 

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Finally a 5 speed
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LPGHemi said:
1) I believe the two plugs per cylinder are to get better emissions. Also you only need 8 coils and not 16 which saves weight.
One plug fires on the normal power stroke and the other lead from that cylinder which has just fired, fires a reciprocal plug on the other bank.
2) Yep, some of the new Hemi's (someone on here will post up which ones) have a system called MDS.....Multiple Displacement System.
This turns off 2 culinders at times of low load on the engine, to save gas. Effectively making the V8 a V6.
It's all seemless and aparently transparent to the user. However, I have seen posts on here and other forums where people say they can tell from the engine pitch which it goes over to V6 mode.
There's no stupid questions, only people who are stupid in not asking in the first place.
This link will explain simply, what the MDS system is and about the two plugs per cylinder.
http://www.allpar.com/mopar/new-mopar-hemi.html
Hope this helps you bud?
Al.

It actually turns off 4 of the cylinders. I know that it started in the Hemi Rams in 2006. I believe it is only in the 1500 and not in the 1500 Megacab or any 2500 models. So really, your 5.7L V8 becomes a ~2.85L 4 cyl.
 

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Whiskey Bent & Hell Bound
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1) 2 plugs per cylinder. One fires on the compression stroke, and the other on the exhaust stroke. Cleaner emmisions basically.

2) BS! Unless its an 06 1500
 

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mheideman said:
1) 2 plugs per cylinder. One fires on the compression stroke, and the other on the exhaust stroke.
:thatfunny Believe what you want... :crazy:
 
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