Okay, I think someone already asked this one. I was wondering if someone could perhaps post the link to a resource site that would have information on Hemi engines. What makes it a Hemi, that sort of thing.
:auto:

 

In a nutshell...the spark plug is in the middle of the cylinder, the spark plug hence is in the valve cover, not like yours, under the exhaust manifold.

 

" Hemi " is the abbreviation of " hemi-spherical " combustion chamber.

The combustion chamber is half sphere shaped with the intake and exhaust valves directly opposite and included away from each other with the spark plug in the centre of the chamber.

- it possesses a much higher volume to surface area ratio , which allows for greater resistance to detonation

- the valves are opposite rather than next to one another, which allows the engine to operate cooler

- the spark plug in the centre, helps flame travel and promotes a better and more efficient burning of the fuel and air mixture

As taken from http://www.hemi.com.au/


[Modified by Robert N, 12:39 PM 3/18/2003]

 

Thanks for the link :cheers:

 

My dad just ask me the same question after seeing the Dodge truck commercial several times. It is interesting how much renewed interest there is in the old hemi design. Craig

 

the HEMI and only ONe other engine shared a fully machined combustion chamber in that era.....

anybody know which other brand...hint...it was a V8.....

GENE

 

Speed kills...Drive rice?????

 

Robert, all correct there, but the simgle most important thing about the HEMI was having the valves canted to either port side....intake tilted upright, and the exhaust tilted near horozontal meant the passages in the head casting had near straight shots once past the valves.....
any airflow guy will tell you the restrictions of a bend in the flow path are horrendous, and the tighter the restrictions, the worse the losses in backpressure/flow efficiency....
SO any wedge head....like SB chebby....engine has to make a severe short bend to allow the exhaust to pass under the car....nearly 180* bend...that is a LOT to turn in a small radius....SO the Hemi limited that to about 90* bend...hense the upper end airflow was SO much more effeicient the engine would with proper cam .....turn on so strong above 4k rpm.... and wind up to about 7k rpm before the thing would finally start slowing power/torque curve....now that is a STOCK engine with a decent cam....
can't do that with any other design...except a more modern thing like a twin OHC thing...or maybe 4 valves, some design today...known as Doghouse

the only thing close in design back when was the BB chebby...with the canted valves...reducing the bends in the passages....not quite as inherently smooth flowing as the HEMI...but cheaper to make....

not only that, but having the valves on 'opposite' sides of the chamber, allowed for much larger valves...and of course a dome head piston to keep compression up....and effective chamber volume down....damn HEMI had valves nearly 2.5 inches diameter...stock....bigger than some freaking pistons for christsakes....;-)))

GENE

 

A couple other things to note.. The Hemi in stock form has a much higher
Volumetric Eficiency that any other V8 of it's era.

The design of the head also aids in exhaust scavenging moreso than a more
traditional chamber.

Modified Hemi's with the right heads will rarely ever run out of airflow, instead
they will make power untill the engine suffers a physical component failure.

My father raced a factory SS/AA car for more than a decade (68 Super Stock
Hemi Barracuda) the engine would scatter before it would run out of airflor
capability. That was a relatively "stock" short block running Bill Mitchell DPort
Dual Plug 900 Heads and Bill Mitchel Alloy X-Ram.

The Hemi is a very interesting beast for certain. Also a costly one.. On the
street though, a 440 6 pack would give a Hemi a run for it's life :) (Many Have)

 

LS1-00, hell if you want that 440 six pak, gimme a 455 Pontiac with tri power or maybe dual quads.....;-)))....all sorts of ways to make POWER....hehe....

OR for that matter a 500ci caddy engine....all opened up and doing right....

but one thing for certain, that damn HEMI would charge down on just about anything....hard to beat raw HP numbers, and they were indeed impressive...

THE BEST sleeper I EVER saw was an old Baker, Commander?? I think, gold stock color..boring....lowered a bit....stock as a stove looking...
in the rear tucked in nice as can be was two posi driven ~10 inch mickeys....

ok, and under the hood, which was only raised a FOOT in front...just a foot...enough to see wall to wall valve covers, not much else...no dual quads, no nothing...much...except DPFI with the most wonderful all aluminum machine shop construction I seen in a while....damn t-body was well...HUGE....
saw it at Carlysle about 7 years ago...maybe 8.....lovely car....just MY idea of a street machine....talk about a MONEY maker...

GENE

 

Ive also heard that the hemispherical shape of the combustion chamber directs the forces of explosion in a more downward direction against the piston creating better power. Its easy to spot a hemi as the ignition wires go right down thru the center of the massive valve covers.

 

I am glad that you all explained it so well to Dwayne. He was under the impression that it meant hemi-roid, I tried to convince him otherwise but he just wouldn't listen.
:lol:

 

The funny thing is that most people forget that DeSoto Fireflites also used Chrysler's first gen Hemi. (As in the 300C and 300D.)

The Hemis of the late 60s and 70s were hard to maintain, often requiring a major expensive tune-up just about every 15,000 miles. Back in the 70s, my father-in-law used to drag against Hemis in his '65 Impala SS Convertible (a tank!) with a 460ci single-carb V8. Essentially, he'd look at the owner of the Hemi. If the guy was under 30, he'd accept the challenge, knowing that the guy wouldn't likely have enough money to keep the car tuned correctly after blowing all his money on a Hemi-powered car. If the guy looked to be older, my F-i-L would decline, knowing that a well tuned Hemi could cream an Impala, even one with a big block torque monster.

By the way, many engines have used hemisperical combustion chamber designs over the years... mostly european sports cars. It's only Mopar that made a huge marketing deal over it.

 

:lolg: :rofl: :lol:

What!!! Thats what you were talking about.. :lolg: