It's "Hemi Day" 4/26!!!!
We all know we love our hemi engine but what is a hemispherical engine?
The classic idea for a hemispherical engine is for the top of the combustion chamber to be a hemisphere. This would minimize heat loss per unit of volume. However, this gives a far too low compression ratio unless you have a very long stroke. Normally, the piston is domed so that it protrudes into the head at top dead centre. This gives it a more of a chamber shape. This design hasnít been used in production vehicles for several decades.
Modern Hemi engines have flatter heads and are vastly more complex than the first models. The chambers are no longer truly hemispherical. They do use a coil-on-plug distributorless ignition system and two spark plugs per cylinder to shorten flame travel leading. This turns into a more consistent combustion and helps reduce emissions.
In 2009, Chrysler made various revisions to the 5.7L Hemi. They introduced a Variable Camshaft Timing (VCT) system. This is essentially variable valve timing that uses an oil control valve which controls oil flow to a unique camshaft sprocket that contains a phasing device. This device either advances or retards the camshaft timing depending on the operation of the oil control valve.
Also, the cylinder heads have been revised to increase flow. And for the first time, the intake manifold is now model specific. Notably, Ram trucks and non-Hybrid Electric Vehicle Chrysler Aspens and Dodge Durangoís use an active intake manifold with a short runner valve to optimize torque and horsepower. Basically at low RPMs, the intake valve is closed, resulting in better low-end torque. The valve is opened at high RPMs to improve horsepower. Chryslerís passenger cars, Jeep vehicles and HEV models of the above donít use that manifold and donít have a short runner valve.
Lastly, Chrysler introduced ďMulti Displacement SystemĒ to the larger V-8 Hemi engine. This system essentially is cylinder deactivation. When the computer recognizes that not all cylinders are needed, it will shut them down to conserve fuel. The modern engine can shutdown a cylinder in .04 seconds and this process is unnoticed by the driver. It has also been proven to be highly reliable and since its introduction in 2005, there have been zero reported issues.
All of these changes resulted in better reliability and gas mileage with more horsepower and torque.
Sunday: Sleeper10Hemi - Shawn from Texas
CASilver04 - Chris from California
If it's your birthday/anniversary/special occasion let us know and we will celebrate with you.
Try your luck at being "Truck of the Month"!! Post a picture and a write up of your ride between the 1st-21st then we vote the 22nd-months end. After the voting the winner will be messaged for email info. The email is for the digital TOTM award. Printing and shipping them was getting pricey and time consuming. The awards will be printable on your end and then you can frame them. Thanks to Keith (charged392) for heading this up!
It's with great sadness that have officially cancelled this year's rally that was scheduled in Fort Worth, Texas. Just a reminder that if you have already reserved your hotel room be sure to call and cancel your reservations! However, read the post under rallies & gathering for "Post covid 19 Picnic" for ideas of when and how we can see our HTC peeps again.
Chatroom is back!! Join us every Thursday evening at 7:00 CST for chatroom. See what going on with the rest of the HTC'ers.
If you have a prayer request you would like to share either add it to this thread or PM me.
*HemiSuperbee - Mark - health concerns
*Rancher - Doug said to take him off the list but I think a quick prayer for his general health issues isn't a bad idea
*Doc's mother - recent fall resulting in fractured femur & surgery, she is currently in rehab
*Studmuffin - Morris' brother-in-law, David, with liver failure
*boedacres - Steve - health issues including diabetes
*SuperBee - John & his wife - health issues
*Those affected and impacted by the Covid 19 virus both physically and financially!
Have a great week and stay safe!!!