what the hell is a hemi??
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From: Berkeley
thanks for all the informative replies--all the reasons why i love this place.
my question is: if a "hemi" designed head makes a more efficient combustion chamber, then why have not more contemporary engines utlized this design?? is it because the design makes the engine's dimensions taller and more bulky--which is a big no-no for todays sleeker car designs??
my question is: if a "hemi" designed head makes a more efficient combustion chamber, then why have not more contemporary engines utlized this design?? is it because the design makes the engine's dimensions taller and more bulky--which is a big no-no for todays sleeker car designs??
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From: Midlothian
The advantage of the hemi layout, with valves angled away from each other, lies with increased valve size, and greatly enhanced porting. This was a major development in large V-8 designs that Chrysler pioneered, although the hemi head had been around for a very long time, including V-16 aircraft engines. The hemis made tremendous power because of their airflow advantages.
Since then, DOHC, pent roof designs, as well as new tricks from piston squish advances, plus precise fuel metering and induction tricks like vtec have prevailed, as they offer their own advantages. Look at the results Honda gets with its 2 liter engines.
Since then, DOHC, pent roof designs, as well as new tricks from piston squish advances, plus precise fuel metering and induction tricks like vtec have prevailed, as they offer their own advantages. Look at the results Honda gets with its 2 liter engines.
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From: Va Beach, VA
The only thing that makes the old Chrysler Hemi different than any other engine with a hemispherical head (I'm not sure if the extreme pushrod/rocker arm angles were Chrylser only or not) is the pistion. The pistion has a very high dome, as in the pistion face stuck up above the block deck. I'm not sure if the new Hemi has this though.
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From: Hawaii
The Hemi design paved the way for some of the technologies being implemented today, even in our own Honda engines. The design and function was an incredible leap for the automotive industry, but with modern electronics, computer aided designs and such, there are a lot more options available today to take advantage of.
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From: Bay Area
Hemi is pure PR hype. It has no place on a moden multivalve motor. Better technology exist today.
Here is a good explanation of a Hemi motor:
http://auto.howstuffworks.com/hemi1.htm
Here is a good explanation of a Hemi motor:
http://auto.howstuffworks.com/hemi1.htm
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From: Longmont, CO
Originally Posted by Hyper-X,Oct 27 2004, 04:11 PM
The idea behind how the Hemi works is being implemented on our cars also, I don't see how it could be PR hype when most modern engines of today use the same design philosophy behind the Hemi.
If HEMI engines have all these advantages, why aren't all engines using hemispherical heads? It's because there are even better configurations available today.
One thing that a hemispherical head will never have is four valves per cylinder. The valve angles would be so crazy that the head would be nearly impossible to design. Having only two valves per cylinder is not an issue in drag racing or NASCAR because racing engines are limited to two valves per cylinder in these categories. But on the street, four slightly smaller valves let an engine breathe easier than two large valves. Modern engines use a pentroof design to accommodate four valves.
Another reason most high-performance engines no longer use a HEMI design is the desire to create a smaller combustion chamber. Small chambers further reduce the heat lost during combustion, and also shorten the distance the flame front must travel during combustion. The compact pentroof design is helpful here, as well.
One thing that a hemispherical head will never have is four valves per cylinder. The valve angles would be so crazy that the head would be nearly impossible to design. Having only two valves per cylinder is not an issue in drag racing or NASCAR because racing engines are limited to two valves per cylinder in these categories. But on the street, four slightly smaller valves let an engine breathe easier than two large valves. Modern engines use a pentroof design to accommodate four valves.
Another reason most high-performance engines no longer use a HEMI design is the desire to create a smaller combustion chamber. Small chambers further reduce the heat lost during combustion, and also shorten the distance the flame front must travel during combustion. The compact pentroof design is helpful here, as well.