I personally don't see the huge mark the hemispherical head made in engine history. The efficiency, to me, is in question too. I'm no scientist or engineer, but hemis don't appear to do much better, if at all, than normal V designs when it comes to MPG. I saw a 50s era Chrysler a couple weeks ago with an old hemi in it and the heads were about twice the size of the ones on my engine. Maybe there was an efficiency increase in torque production, but it couldn't have been that big an increase, as it didn't take hold in the Ford or GM camps, and still doesn't today.

From my vantage point, Chrysler's hemi has been little more than a marketing and PR win over the last 50+ years. Chrysler first toyed with this design in the late 40s, and fit multiple foreign boutiqe cars with them, such as the recursor to the original AC cobra. But that doesn't really prove the breed in those instances.

People talked about 409s and Cobra Jets and 427s just as much as they talked, and still talk, about hemis. Maybe Chrysler did well at the drag strip, but I'm not a top fuel dragster kind of guy. =\

To me, the "hemi" is just something for Chrysler fans to rally around, which is fine. For guys have their 302s and 428s, Chevy guys have their 327s and 396s.



FYI: another "unknown" car that used hemispherical heads was the Z31 300ZX.

 

[QUOTE=Elistan]Then again, I rather doubt that F1 engines use a hemi design.

 

here's a page that shows how the Hemi head design differs from other styles:
http://www.thehemi.com/heads.php

There is more to head design than just the combustion chamber, the valvetrain and port design can play a huge part in engine performance and potential.

It is worth noting that the hemi design and pentroof designs are essentially the same - pentroof is simply a modification of the topography of the combustion chamber, the essential characteristics are the same, i.e. opposed valves, rather than side-by-side. In the link I posted, the top two images are hemi/pentroof designs, while the bottom two are bathtub or wedge design, with parallel valves. Hemi/pentroof designs are more expensive to manufacture, but are more efficient, power-wise. Chrysler didn't invent the hemi design, but they did sell a ton of engines using a proven performance design. I'd be very surprised if modern F1 engines didn't use a pentroof combustion chamber.

It is interesting that the howstuffworks.com article totally missed the thing that makes the hemi design significant - the opposed valves. Most engines have valves that are parallel, with the spark plug off to one side of the cylinder. The common wedge design is efficient, with very little unburned fuel and highly tolerant of detonation, but the valve position limits valve size, whereas an opposed valve design allows for larger valves and a centrally located spark plug. Total power output can be greater in the hemi design, but it makes the engine physically larger, more expensive to manufacture, less tolerant of detonation, and potentially less fuel efficient, which is why it isn't universal.

 

I believe the big, thundering nitromethane and alky drag engines do, but the passenger car Hemis had 1 plug per cylinder.

Older BMW 6s have hemispherical combustion chambers as well.

-Mirror

 

The new passenger Hemi's are dual plugged, as posted earlier.

 

Ah yes, I was referencing the old stuff. Duly noted on Chrysler's new offering.

Cheers,
-Mirror

 

HEMI: old school.
Back in the 50

 

[QUOTE=Dr. WOT,Jan 15 2004, 01:11 PM]

True, but they way you said that casts a very negative light.

 

Not allowed. Racing restrictions. If they could they would.

Also as stated in this thread already Honda and most other auto companies do use some of the design techniques used in a Hemi engine. So everybody in here that thinks it's just marketing needs to think again.