Dodge truck Hemi engine question

[Kaspian]

"

YEAH, IT'S GOT A HEMI® V8. SWEEEET. Ah, the 5.7-liter HEMI® V8. This engine generates up to 345 horsepower at 5,400 RPM (330 HP in Ram 3500) and 375 pound feet of torque at 4,200 RPM. HEMI V8 doesn't merely jump over the competition. It leaps. With electronic throttle control. Aluminum cylinder heads. Hemispherical combustion chambers. High compression ratio. And a design that utilizes 2 spark plugs per cylinder to burn fuel more efficiently - and leave the competition eating Dodge dust. HEMI is a registered trademark of Chrysler Motors LLC.

So, are we talking about 16 spark plugs here? And how does it compare to the older 5.9L Magnum engine (the one I have in my '99 Ram)? I know it has more horse power but is it more fuel efficient?

 

[iamwiz82]

Originally posted by: Kaspian
"

YEAH, IT'S GOT A HEMI® V8. SWEEEET. Ah, the 5.7-liter HEMI® V8. This engine generates up to 345 horsepower at 5,400 RPM (330 HP in Ram 3500) and 375 pound feet of torque at 4,200 RPM. HEMI V8 doesn't merely jump over the competition. It leaps. With electronic throttle control. Aluminum cylinder heads. Hemispherical combustion chambers. High compression ratio. And a design that utilizes 2 spark plugs per cylinder to burn fuel more efficiently - and leave the competition eating Dodge dust. HEMI is a registered trademark of Chrysler Motors LLC.

So, are we talking about 16 spark plugs here? And how does it compare to the older 5.9L Magnum engine (the one I have in my '99 Ram)? I know it has more horse power but is it more fuel efficient?

Yes, 16 spark plugs, and good luck changing the ones in back. 😛 It's a night and day difference between the 318/360, though, in terms of performance. Gas mileage is about the same as my old 5.2. In my Hemi, this tank I have not been driving as hard and I am getting about 14MPG, all city. I do not have an MDS Hemi, though.

 

[mwmorph]

16 spark plugs create cleaner emissions. That's about all there is to it, some cars in the past used this, the most common example were Ford Ranger 4 cylinders.

 

[Kaspian]

Originally posted by: iamwiz82
Yes, 16 spark plugs, and good luck changing the ones in back. 😛 It's a night and day difference between the 318/360, though, in terms of performance. Gas mileage is about the same as my old 5.2. In my Hemi, this tank I have not been driving as hard and I am getting about 14MPG, all city. I do not have an MDS Hemi, though.

Oh, no, no, no. I dont change spark plugs. Thats what the mechanics are for. They have families to support you know🙂 No really all jokes aside I'm not concerned about their location. I dont do any work in my vehicles because I dont know jack squad about them.

 

[Kaspian]

Originally posted by: mwmorph
16 spark plugs create cleaner emissions. That's about all there is to it, some cars in the past used this, the most common example were Ford Ranger 4 cylinders.

Why is it that they are not doing it in more vehicles? Could it be that makers are affraid the customer may not purchase their vehicle because higher maintenance cost? Just curious.

 

[Hyperlite]

Originally posted by: Kaspian

Originally posted by: mwmorph
16 spark plugs create cleaner emissions. That's about all there is to it, some cars in the past used this, the most common example were Ford Ranger 4 cylinders.

Why is it that they are not doing it in more vehicles? Could it be that makers are affraid the customer may not purchase their vehicle because higher maintenance cost? Just curious.

it probably has more to do with space. its a helluva lot easier to implement that on larger engines. as to why it hasn't been applied more in that area, i have no idea. perhaps some manufacturers don't deem it worth the extra cost/complexity.

 

[exdeath]

It's mostly useful on engines with a bigger bore. Uniform flame front propagation starts to get tricky when you have a large cylinder bore.

 

[Zenmervolt]

Dual plug ignition really only becomes helpful on engines that have large cylinder areas because they help to make sure that the flame front reaches all areas. In smaller engines, a single plug can often be sufficient to ensure complete burn.

Additionally, the spark plug takes up space, so unless you have a large bore, you begin to have trade-offs between valve area and that second spark plug, to where you may lose more power and efficiency from having to make the valves smaller than you get from having the second spark plug. There are also more basic packaging concerns, especially on OHC engines. Remember that the Hemi is a pushrod design, so there's no overhead camshafts competing for space above the block either, which also gives more flexibility in placement and number of spark plugs.

ZV

 

[Zenmervolt]

Originally posted by: exdeath
It's mostly useful on engines with a bigger bore. Uniform flame front propagation starts to get tricky when you have a large cylinder bore.

Curse your faster typing! 😛

ZV

 

[Kaspian]

Originally posted by: Zenmervolt

Originally posted by: exdeath
It's mostly useful on engines with a bigger bore. Uniform flame front propagation starts to get tricky when you have a large cylinder bore.

Curse your faster typing! 😛

ZV

Your posts are one min apart.:laugh:

 

[cardiac]

Zenmervolt, isn't it kind of a moot point to have 2 plugs in a hemispherical combustion chamber? That was part of the reason for the design, to keep flame travel equidistant around the chamber? Wouldn't dual plugs have a bigger advantage in a standard pushrod motored combustion chamber? Like the 6.0 liter GM?

Thanks,

Bob

 

[Zenmervolt]

Originally posted by: cardiac
Zenmervolt, isn't it kind of a moot point to have 2 plugs in a hemispherical combustion chamber? That was part of the reason for the design, to keep flame travel equidistant around the chamber? Wouldn't dual plugs have a bigger advantage in a standard pushrod motored combustion chamber? Like the 6.0 liter GM?

Thanks,

Bob

"Hemi" was, and still is, mostly a marketing term. Engines from Ford and Chevrolet have incorporated hemispherical heads for at least as long as Chrysler engines, and many modern engines have hemispherical heads as well.

A hemispherical head helps the flame front travel optimally, dual plugs help the flame front travel completely. The central placement of the spark plug helps make the most of the pattern in which the flame front propagates, but it doesn't make it propagate any faster. If the flame front cannot fill the cylinder fast enough because the chamber is too large, it doesn't matter where the plug is. Dual plugs give you two flame fronts, helping more of the mixture burn within a given time.

ZV

 

[cardiac]

Originally posted by: Zenmervolt

Originally posted by: cardiac
Zenmervolt, isn't it kind of a moot point to have 2 plugs in a hemispherical combustion chamber? That was part of the reason for the design, to keep flame travel equidistant around the chamber? Wouldn't dual plugs have a bigger advantage in a standard pushrod motored combustion chamber? Like the 6.0 liter GM?

Thanks,

Bob

"Hemi" was, and still is, mostly a marketing term. Engines from Ford and Chevrolet have incorporated hemispherical heads for at least as long as Chrysler engines, and many modern engines have hemispherical heads as well.

A hemispherical head helps the flame front travel optimally, dual plugs help the flame front travel completely. The central placement of the spark plug helps make the most of the pattern in which the flame front propagates, but it doesn't make it propagate any faster. If the flame front cannot fill the cylinder fast enough because the chamber is too large, it doesn't matter where the plug is. Dual plugs give you two flame fronts, helping more of the mixture burn within a given time.

ZV

Well said! Thanks for the great answer! I know that Ford had a true hemi-head back in I think 1968-69? A particular version of the 428 maybe?

Thanks for the explanation.

Bob

 

[herm0016]

the ford model T is the only engine i have seen that is truly a hemi head. the piston even has an almost completely hemispherical dome. the new "hemi" is just a marketing term.

 

[Summitdrinker]

yep the new hemi, really isn't a hemi, getting a true hemi to pass emission maybe tuff

the old 50's mopar hemi (331, 352,391)was a really hemi, the 426 hemi was very close

then you have big block chevies, 351 clevelands etc these were not real hemi's but they didn't have the valves in a line, then there was also the old mopar 318 poly head, which was a odd ball too