Lately, there have been abundant car commercials advertising a truck with a hemi. One commercial even said “It has a hemi. Do you really need to know anything else?”
So what is it, what does it do, what makes it so special, and do I need to care?
Kind of engine i believe
I means the combustion chamber in the heads has a hemispherical shape, rather than the cheaper flat shape. It means increased thermal efficiency, which translates to slightly better fuel economy and slighty more horsepower per cubic inch of engine displacement. They’ve been around since the 70s, but advertisers are only now seizing on it as feature to tout.
Others more knowledgeable than I could give a more complete answer, but I’ll do my best.
The Hemi was an engine that was popular during the “muscle car” era of the late 60s/early 70s. Chrysler put it in cars under both its Plymouth and Dodge nameplates. The name “Hemi” refered to the curved shape of the combustion chambers, IIRC.
A couple of years ago, they revived the name and slapped it on a new engine as a marketing gimick.
It’s a type of engine, it makes the car go forward, it has some historical significance, and no.
Hemi engines have hemispherical (as opposed to cylindrical) combustion chambers.
Some other hemi-worshipping site.
Car people tend to be fiercely loyal to their favorite brand/model/tech, to the point of a near-religious zeal, of course, so I’d take the listed benefits with a big old grain of salt. Hemishperical combustion chambers have been around for a long time (invented in the 1930s, available on production cars in the 1950s), but they’ve always been relatively rare in production cars. If they were really so great, I expect they’d be more common.
Wow, so many responses so quickly! All the guys must be surfing the Dope right now…
Thank you!
Although true “hemis” are rare, the head design on engines with more than 2 valves per cylinder (generally 4 valves, but thre are 3 and 5 as well) are usually a modified hemispherical shape. Essentially, they are refinements to the “hemi” concept. If you take a wider view on things, hemis are quite common.
The old hemis truly were beasts. IIRC, upon their introduction they began to blow everything else off the track and I think were eventually banned form some competitions. There was a thread here awhile back where some pretty knowlegable folks defined their characteristics and history pretty well. You might try searching for that.
Skip the search…
Here you go.
I am so glad you asked this. I’ve been wondering about it for days.
BTW, the post above is meant entirely in earnest and isn’t supposed to sound snarky. I really was wondering if it was some sort of “real guy” secret 
Hemi…ah, sweet Hemi…awakes oh, that was my first gf’s pet name, if you wanna know. I always wondered what she is upto now. looks like she invented a truck engine. I’m so proud!!
clap clap.
Any so now you know what (or more correctly who) Hemi is. Always happy to help
Bruce Springsteen, Born to Run, 1975
Or to quote Sir Mix-a-lot:
“[her] butt shook like a 426 Hemi”
From the aspect of putting out power, it’s hard to argue that the Chrysler Hemi was not the greatest thing ever. 50 years after the initial design, it’s still the engine of choice for unlimited drag racing. However, what limited the Hemi was economics. The combustion chamber itself was more expensive to produce and the requirement that the valves be arranged at different angles made the valve train much more expensive.
The fastest cars in the world ALL run Hemi’s. They race down a straight quarter-mile track in less than 5 seconds at over 300 mph.
Here are some pictures of Top Fuel Dragsters:
(Click on drivers name to see the car.)
http://www.nhra.com/2003/gallery/index.html
These puppies generate over 5000 horsepower burning almost a gallon of fuel per SECOND. Their fuel? A mixture of nitroglycerine and methane alcohol.
(For comparison, a stock Corvette has about 350 horsepower.)
But are street Hemis as powerful as racing Hemis?
If you two two Dodge trucks (since the only comercials I’ve ever seen for Hemis are the Dodge) that are exactly the same, aside from one having a Hemi and one not, how much difference in power would you have?
Aside: Who the hell needs that much power for driving around the city, anyway?
nitpick: Nitromethane is it’s own molecule (CH3NO2), not a mixture of anything.
Handy? Is that you?
While there are enough good, factual answers in this thread that I don’t feel the need to add anything, I will say that the use of the simple term “hemi”, as used in the commercials, is highly misleading. The mere fact that the engine sports hemispherical-shaped combustion chambers does not in itself mean that any one engine is more powerful than any other. And as someone noted accurately earlier, many multivalve engines are actually improvements on the “hemi” design anyhow. Beside the fact that due to valve placement, flow issues, cylinder turbulence, etc. there is not really any ideal, single shape that will work for all situations.
It’s also interesting to note how many hemi engines are out there, if you listen to the boasting of High School males (as well as those who “peaked” in High School). In my time, I saw an Olds Cutlass with a 350 Chevy “hemi”, a Mercury Montego with a “hemi”, and even a Pontiac Aster Wagon with a “hemi”. And I’ll never forget the Pinto with a “426 hemi” in it. :rolleyes:
KenGr, I think you had it right with the valvetrain comment. A friend of mine in one of the Chrysler engine R&D departments (diesel, actually) claims that the valvetrain arrangement difference was by far the primary expense.