Hemi engines
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 26
From: Austin Texas
True Hemi engines haven't been sold by a new car dealer for years.
The current "Hemi" by whatever Chrysler is calling themselves this month is not a true Hemi. The term Hemi meant hemispherical combution chambers and no current engine has hemispherical combustion chambers. The current "Hemi" by Chrysler is such an inefficient design that they have to use two spark plugs to get acceptable ignition.
The current "Hemi" by whatever Chrysler is calling themselves this month is not a true Hemi. The term Hemi meant hemispherical combution chambers and no current engine has hemispherical combustion chambers. The current "Hemi" by Chrysler is such an inefficient design that they have to use two spark plugs to get acceptable ignition.
Team Owner
Joined: Feb 2001
Posts: 27,254
Likes: 136
From: Short Hills, NJ
There are a lot of similarities between the current Chrysler 5.7L/6.1L Hemis and the GM LS motors. The Hemis are good engines with great cylinder heads and can be modified to make some strong power though I prefer the aluminum block (Hemis are iron) of our LS motor more. 
Safety Car
Joined: Jan 2004
Posts: 4,974
Likes: 14
From: Pinellas Park Fl
St. Jude Donor '08-'09 & '12, '14
True Hemi engines haven't been sold by a new car dealer for years.
The current "Hemi" by whatever Chrysler is calling themselves this month is not a true Hemi. The term Hemi meant hemispherical combution chambers and no current engine has hemispherical combustion chambers. The current "Hemi" by Chrysler is such an inefficient design that they have to use two spark plugs to get acceptable ignition.
The current "Hemi" by whatever Chrysler is calling themselves this month is not a true Hemi. The term Hemi meant hemispherical combution chambers and no current engine has hemispherical combustion chambers. The current "Hemi" by Chrysler is such an inefficient design that they have to use two spark plugs to get acceptable ignition.
Le Mans Master
Joined: Jun 2004
Posts: 6,269
Likes: 50
From: Dallas Texas
St. Jude Donor '06-'07-'09-'10
The value of the Hemi design over the typical wedge shaped combustion chamber is that the valves are opposite each other at approx. 90 degrees rather than side by side as in the wedge. This allows for a more straight thru intake/exhaust flow, but requires either dual cams or an elaborate rocker arm set up and adds to the engine's overall width, weight, and complexity.
Race Director
Joined: Mar 2005
Posts: 10,399
Likes: 26
From: Austin Texas
The hemi design was good for it's time of the 50's and 60's but the hemi head/piston design wasn't the reason for the popularity of the Hemi. Those early Hemi's were cast from a high nickel content block with great for the time dimension control/stability AND had forged internals so added power didn't require a new block or heads.
A true hemispherical head calls for a domed piston. Intake and exhaust flow around a domed piston is difficult to control for peak efficiency and power. The current Hemi's use an "almost" hemispherical head and a piston design that requires two spark plugs to get a complete burn. Look at the power produced from the current Hemi, the 10+ year old LS1 design does better on HP per Cubic Inch without a hemi design and without 2 spark plugs per cylinder.
The Hemi is/was a great advertising gimmick for Chrysler but not a great advance in power or efficiency.
A true hemispherical head calls for a domed piston. Intake and exhaust flow around a domed piston is difficult to control for peak efficiency and power. The current Hemi's use an "almost" hemispherical head and a piston design that requires two spark plugs to get a complete burn. Look at the power produced from the current Hemi, the 10+ year old LS1 design does better on HP per Cubic Inch without a hemi design and without 2 spark plugs per cylinder.
The Hemi is/was a great advertising gimmick for Chrysler but not a great advance in power or efficiency.
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Team Owner
Joined: Sep 1999
Posts: 41,732
Likes: 1,718
From: Springfield MO
With a true hemi head there is much more room to put in larger valves since they are across from each other instead of next to each other and the intake valve port is in line with the intake manifold ports and the exhaust ports are lined up with the exhaust manifold. Nice direct, large ports. To make big power, you need to move a lot of air and big valves are the answer.
Last edited by JoesC5; Feb 19, 2010 at 02:07 PM.
Melting Slicks
Joined: Aug 1999
Posts: 3,422
Likes: 9
From: Rockaway, NJ
With a true hemi head there is much more room to put in larger valves since they are across from each other instead of next to each other and the intake valve port is in line with the intake manifold ports and the exhaust ports are lined up with the exhaust manifold. Nice direct, large ports. To make big power, you need to move a lot of air and big valves are the answer.
Racer
Joined: Apr 2005
Posts: 351
Likes: 0
From: Louisville Kentucky
I don't know anything about the current Chrysler design but the 426 Hemi that I had in my 1970 Dodge Charger was very powerful. It made that automatic transmission, heavy car with 3.54 gears feel light. My 1971 440 6BBL Roadrunner with a manual and 4.10's was a little quicker for about 100 yards but after that the Hemi would walk on away. I actually passed on my first Vette purchase in favor of the RR. It was a 427/390 with a manual and 3-2's. The RR was quicker, which is why I bought it. They were about the same price. What a moron I was that day!
Safety Car
Joined: Jan 2008
Posts: 4,711
Likes: 3
From: Middle of No where AK
You have an LS based motor. One of the best power producing motors made to date. With very little modification (cam, ported heads) it will pretty much torch anything out there and still get decent gas mileage. No other motor can boast that type of performance and economy. Im pretty dang inmpressed with GM's engineering on this particular application.
Safety Car
Joined: Nov 2006
Posts: 3,860
Likes: 5
From: Tampa FL
Burning Brakes
Joined: Apr 2009
Posts: 1,155
Likes: 0
From: Kansas City MO
all marketing. I have the 5.7 Hemi in my yellow truck in my avitar. they are a lot like our LSx motors. big difference is that chrysler locked down the PCM and very few companies have been able to crack it to allow tuning. compare that with our motors which have a lot of options with tuning tools. I know there are some basic tuning tools out there for the hemi but they do not compare to the ones for our LS series motors.
LS motor CAN make power just by looking at it the wrong way.
LS motor CAN make power just by looking at it the wrong way.
Team Owner
Joined: Apr 2001
Posts: 26,794
Likes: 614
From: Elmhurst, IL (West Suburb of Chicago) & Home of MEGA Horsepower
St. Jude Donor '06
True Hemi engines haven't been sold by a new car dealer for years.
The current "Hemi" by whatever Chrysler is calling themselves this month is not a true Hemi. The term Hemi meant hemispherical combution chambers and no current engine has hemispherical combustion chambers. The current "Hemi" by Chrysler is such an inefficient design that they have to use two spark plugs to get acceptable ignition.
The current "Hemi" by whatever Chrysler is calling themselves this month is not a true Hemi. The term Hemi meant hemispherical combution chambers and no current engine has hemispherical combustion chambers. The current "Hemi" by Chrysler is such an inefficient design that they have to use two spark plugs to get acceptable ignition.
100% Very well put. The classic hemispherical combution chambers is also a dominant force in professional drag racing today and has been so for many, many years (since the mid 60s) with most top fuel (funny cars and dragsters) running them today still. 
The mystique behind the HEMI engine has a big part to do with the way MOPAR domininted with the Hemi in the the mid to late 60s on the dragstrip and also Nascar Circuit.
Safety Car
Joined: Jan 2004
Posts: 4,974
Likes: 14
From: Pinellas Park Fl
St. Jude Donor '08-'09 & '12, '14
all marketing. I have the 5.7 Hemi in my yellow truck in my avitar. they are a lot like our LSx motors. big difference is that chrysler locked down the PCM and very few companies have been able to crack it to allow tuning. compare that with our motors which have a lot of options with tuning tools. I know there are some basic tuning tools out there for the hemi but they do not compare to the ones for our LS series motors.
LS motor CAN make power just by looking at it the wrong way.
LS motor CAN make power just by looking at it the wrong way.
