hemi - Dodge Dakota Forum

Subject: hemi
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What is the difference between a hemi engine and just the plain old engine? What is so exciting about this engine coming out?

Wayne
Dodge Dakota
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11/18/2002
02:21:16

RE: hemi
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Hemi is short for the hemispherical shape inside of the heads. While other engines have had this feature none have capitalized on it like Dodge and Plymouth did back in the late sixties with their 426 cu. in. HEMI. It has a sort of a cult following not to mention that the new one at 345 cu. in. (5.7 L) puts out 345 h.p. and has potential for more. For us gear heads this is a chance to run with the bigger engines that the other guys are coming out with. The Lightning is only rated at 380 h.p. A good tuner can get that much out of the new Hemi with no trouble.

Jon
Dodge Dakota
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11/18/2002
08:32:50

RE: hemi
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Except these new hemi's don't have the exact sabe combustion chambers as the old ones because a true hemi wouldn't meet todays emissions standards.

-Jon

JayWingate
Dodge Dakota
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11/18/2002
09:12:52

RE: hemi
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A hemi has a round combustion chamber with the sparkplug located in the center of the dome. With advances in fuel injection and computer controls on engines, these engine can meet emission standards. The old hemi's use an carb and a crude electronic ignition by today's standards. The hemi cylinder head was a very heavy piece of cast iron. In fact the whole block was very heavy, but they developed great horsepower. With the advances in metal, the weight has come down to make these engines practical again.

Lattimer
Dodge Dakota
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11/18/2002
09:41:41

RE: hemi
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The big thing about the Hemi is the combustion chamber. It is basically half of a sphere (HEMI-sphere). This shape allows a greater valve area using only two valves per cylinder. Most engines have a smaller, flatter combustion chamber. Therefore, you can use a fairly low-tech engine design, with a single cam and push rods, and still get the true-truck low end torque most of us want. But, with the increased valve area, and increased combustion chamber volume, the flow of the Hemi-head allows the engine to make a lot of torque throughout the powerband. Essentially, its a very simple design that makes a lot of power without a lot of extra, complicated hardware in the engine. Historically, nothing could match up with the old Hemi's power for power, and especially not displacement for displacement.

xxx
Dodge Dakota
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11/19/2002
14:21:47

RE: hemi
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If the hemi is so great, then why did they stop making it?

Wayne
Dodge Dakota
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11/19/2002
16:55:53

RE: hemi
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Several reasons not the least of which was gas mileage. Basically the same reason chubby and ferd stopped making their big block motors. HEMI clones are still made by the aftermarket companies for racing purposes. Most of the fastest classes are using designs taken directly from the original 426 HEMI.

cbmoose
Dodge Dakota
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11/19/2002
19:56:21

RE: hemi
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Actually, you guys have some of the Hemi lore and history right. But...the original reason why the Hemis were discontinued in favor of the "A", which was polyspherical, and the "B" engines, which were wedges, was cost of manufacture. Now that they're being made in Saltillo, MX, the cost has come down. Plus new methods of material manufacture, like CAD/CAM machining, made the new 354" possible, from a financial standpoint.
The 426 Hemi does not have true hemispherical heads, like the "early" Hemis. The heads were designed to work with the existing "RB" series block basic design, and so compromises were needed. The rest, as they say, is history.
Hemi heads were first developed for radial aircraft engines a long time ago. Every Japanese motorcycle I've owned, from a Honda CL450 to a Kawasaki 900 Z-1 has hemi heads. In fact, most if not all DOHC engines have hemi design.
Wayne, from what I've read about the new Hemi, it's smaller, lighter, much more powerful, cleaner emissions-wise (thanks in part to its two plug per cylinder design) and gets better fuel efficiency than the LA series 360 Magnum it replaces.
Yes, the new 426 crate Hemi can be purchased from your local Dodge dealer, available in 426, 472, and 528 cubic inch sizes. The original 426 had a reputation for having some weak spots, spots that have been eliminated in the new Mopar Performance engines, since they aren't mass-produced for a production line, where costs have to be kept to a minimum. In fact, with MP engines available for 440 and 360 inch applications, the current line of thought is to remove the nice, original, numbers-matching engine from your Mopar musclecar, drop in a crate engine, and have fun with the car instead of worrying about fragging the engine every time you start it.
I looked at a new Hemi Ram 2500 4X4 the other day. List price was $29,000, which wasn't bad compared to the $26,000 for a '01 Ram 1500 4X4 with the same (SLT) package. But I haven't seen any on the streets of western PA yet.
Wonder how the '04 Dakota R/T will sell...?

Wayne
Dodge Dakota
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11/19/2002
20:04:29

RE: hemi
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cbmoose, you list the new Hemi as a 354. I remember Mopar listing is as a 353 back when they were talking about putting it in Charger. In fact it is a 5.7L which is ~345. Bore and stroke measurements calculate to with in ~.5 of that number. Thanks for the history lesson on the old Hemi.

Lattimer
Dodge Dakota
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11/20/2002
13:16:32

RE: hemi
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Remember, the liter sizes of engines are usually rounded quite a bit. As cubic engines are a smaller unit of measure, so the measuremnt in c.i. is usually more precise. 5.7 liters is 347.83534 cubic inches. However, 354 cubic inches is 5.801020 liters, and 353 c.i. is 5.784633 liters (thanks to my handy TI-85 calculator).

When naming an engine (i.e. 3.7, 4.7, 5.7) many manufacturers like to keep the family of engines sounding similar. So, in the case of the hemi, I'm sure the logo of 5.7L is a little more marketing than mathematical perfection. If you look at the entire chrysler line, you will find a 2.7, 3.7, 4.7, and 5.7. Coincidence??

Shawn

SuperBee
Dodge Dakota
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11/20/2002
14:42:07

RE: hemi
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(thanks to my handy TI-85 calculator).

BAH, NEEDS MORE 86!!!

cbmoose
Dodge Dakota
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11/20/2002
18:34:25

RE: hemi
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I don't know how I got the 354 number stuck in my head, but there it was. Back before the 426 Hemi was popular, the hot ticket was the 392 Hemi, from the original series. Don Garlits and Stone-Woods-Cook rode the 392 to fame and fortune in the halcyon days of drag racing, pre-1965. The really neat thing was that Chrysler made Hemis in a bunch of displacements, from 392 to 241 inches, I think. There are a bunch of sites on the Web that are devoted to Hemi genealogy. Now, as to the new engine: I haven't been able to find anything here on the Web which would indicate that the Pettys, or anyone else, are doing the R&D work necessary to certify the new engine for NASCAR, although I'd bet my eye teeth that it's going on, and NASCAR is waiting for the results to see how small the restrictor plate will be. I've also read rumors that the Hemi will be enlarged, either to 400 or 383 (for obvious historical reasons)cubes. This will accompany the current 4.7 cammer's enlargement to 318 cubes. According to one tech story I've read on the Web, Chrysler considered making the new Hemi a DOHC design, then a SOHC design, and finally stuck with pushrods to keep the costs down, and the engine simple. Rich Ehrenberg, of Mopar Action, wrote an excellent tech article about the new Hemi. You can find a link to it at moparaction.com.

Dan Blodgett
Dodge Dakota
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11/20/2002
19:18:09

RE: hemi
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Another reason Chrysler went with pushrods for the new hemi engine was to to lower the height of the overall engine package. Think about how low the hood was on the "Hemi" showcar. DOHC or even SOHC designs add plenty of height to an engine. The packaging designs of a potential production "Hemi" showcar (with allowances for the 3.5 and 4.7 engine options), forced the hoodline up soo far the design was never shown to upper management! Not to worry, the new hemi engine will rock! The pushrods are short enough to not be a rev limiter like older designs.
Dan.

wantanRT
Dodge Dakota
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12/01/2002
00:36:11

RE: hemi
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i lika da joose...

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