what exactly is A Hemi?
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From: western pa,zelienople
Real basic...... the spark plug is centered directly above the piston. This pushes the piston stright down in stead of down and over against one side of the cylinder. So the plugs go into the valve covers.
Post Fiend
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From: Missouri
HEMI is short for hemispherical combustion chamber. The combustion chamber is in the shap of half of a sphere. The piston heads are somewhat the same. The valves are angled at each other on both sides therefore allowing much more direct paths for air to get into the cylinder and larger valves than a wedge type head can allow. I'm not sure what you mean by pushing the piston straight down Bob.
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From: philly pa
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From: Tampa
Don't bust on the hemi. Ford made them too, note the boss 429. It makes for a cleaner burn in the combustion chamber witch means more HP.
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From: Monterey bay area
THe hemispherical combustion chamber also helps mitigate detonation for high compression applications....
This is usually due to the efficient concept of radiating the pressure wave from the upward-bound piston into many equidistant points in the combustion chamber as opposed to bouncing it off the quench in hopes of diffusing it into smaller less significant pressure waves...
The more deliberate paths of the ports also help the V.E.
I would also like to note that almost all if not all 4-5 valve per cylinder heads
have this hemishperical combustion chamber....
with the spark plug centered about the center of the chamber it also helps recreate the most efficient explosion inside the chamber during the powerstroke....we know explosions are spherical in their most efficient form....
This explains why the hemi was so efficient and provided legendary power...for both Ford and Mopar.
This is usually due to the efficient concept of radiating the pressure wave from the upward-bound piston into many equidistant points in the combustion chamber as opposed to bouncing it off the quench in hopes of diffusing it into smaller less significant pressure waves...
The more deliberate paths of the ports also help the V.E.
I would also like to note that almost all if not all 4-5 valve per cylinder heads
have this hemishperical combustion chamber....
with the spark plug centered about the center of the chamber it also helps recreate the most efficient explosion inside the chamber during the powerstroke....we know explosions are spherical in their most efficient form....
This explains why the hemi was so efficient and provided legendary power...for both Ford and Mopar.
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From: western pa,zelienople
[QUOTE]Originally posted by Capone
[B]....
This is usually due to the efficient concept of radiating the pressure wave from the upward-bound piston into many equidistant points in the combustion chamber as opposed to bouncing it off the quench in hopes of diffusing it into smaller less significant pressure waves...
I said that........well.........kinda
[B]....
This is usually due to the efficient concept of radiating the pressure wave from the upward-bound piston into many equidistant points in the combustion chamber as opposed to bouncing it off the quench in hopes of diffusing it into smaller less significant pressure waves...
I said that........well.........kinda
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From: Chicago Area
I think it's interesting that Dodge is getting so much hype out of their new "Hemi", when it bears no resemblence to the old 426 Hemi, and in fact, may not really be a hemi at all!
"Hemi" comes from hemisphere: "half of a sphere". The old hemi's did have a half of a sphere, which necessitated the characteristic huge valve covers to accomodate the resulting widely splayed valve stems. The new engines have a rounded combustion chamber (very common), but it does not seem to be a hemisphere.
But I guess the marketing guys can define these things any way they want!
"Hemi" comes from hemisphere: "half of a sphere". The old hemi's did have a half of a sphere, which necessitated the characteristic huge valve covers to accomodate the resulting widely splayed valve stems. The new engines have a rounded combustion chamber (very common), but it does not seem to be a hemisphere.
But I guess the marketing guys can define these things any way they want!
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Yep, Dodge owns the Hemi name and have used it for their Marketing to make themselves big bucks.
A lot of people were naive when Dodge said they were coming out with a Hemi Ram. I mean what the heck did people think, that they were going to come out with a 5500 lbs. truck that was gonna do 0-60 in 5 seconds? They needed to use their brain... a 5500 lbs. (QC 4x4) flying brick doing 0-60 in 7 somethin' seconds is pretty darn good, and the 2WD RegCab doing 0-60 in around 6 give or take is certainly nothing to put down.
It destroys its predessesor in every respect... weight, speed, power, gas mileage, and is certainly on par with all its competition.
Marketing Hype? Yes, it makes money.
god of all engines? No.
Good engine? Yes.
A lot of people were naive when Dodge said they were coming out with a Hemi Ram. I mean what the heck did people think, that they were going to come out with a 5500 lbs. truck that was gonna do 0-60 in 5 seconds? They needed to use their brain... a 5500 lbs. (QC 4x4) flying brick doing 0-60 in 7 somethin' seconds is pretty darn good, and the 2WD RegCab doing 0-60 in around 6 give or take is certainly nothing to put down.
It destroys its predessesor in every respect... weight, speed, power, gas mileage, and is certainly on par with all its competition.
Marketing Hype? Yes, it makes money.
god of all engines? No.
Good engine? Yes.
Posting Guru
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From: Chicago Area
I didn't say it isn't a good engine - that remains to be seen - only that it is nothing at all like the 426 Hemi, from which it inherits it's image. And I don't think it even has a true hemispherical head as an engineer would define it.