I know it has something to do with the head, but what exactly is a "hemi"?

 

the cumbustion chamber is hemispereical

 

The above is true, that 's where "the Hemi" got it's name from.
But you are probably referring to the famous line of Plymouth/Chrysler engines that made racing history in NASCAR in the late 60's/early '70's.
The 426 Hemi, sold to the public for race homologation, in a select few cars. Road Runners, Chargers,etc.
The fastest car I was ever in was a 1970 426 Hemi, Super Bee.
My god was it fast for a "street" car.
My friend pinned the 140-150?? mph speedo in about 10-15 seconds, on open strech of closed highway. That was scary as hell, but still fun. LOL Other car companies have made hemi-head engines too, just none as famous as the plymouth/chryslers. And now Daimler/whatever it's called is trying to bring back some glory days. LOL

 

[QUOTE=4crx4me]LOL Other car companies have made hemi-head engines too [QUOTE]

yeah but they did not market it like Chrylser did, IMO they are trying to bring back sales and i personally hate Dodge, Chrylser, and Jeep i would never own one.

I don't believe that a Super Bee shot ot 150 in 10sec i have ridden in a few of them and they are not nearly that fast at all. Stock muscle cars were lucky to ever get out of the 14's

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 99blackcivicSi &raquo;</TD></TR><TR><TD CLASS="quote">

yeah but they did not market it like Chrylser did, IMO they are trying to bring back sales and i personally hate Dodge, Chrylser, and Jeep i would never own one.

I don't believe that a Super Bee shot ot 150 in 10sec i have ridden in a few of them and they are not nearly that fast at all. Stock muscle cars were lucky to ever get out of the 14's

</TD></TR></TABLE>
Answer to first thought.: So, don't buy one, then. Who cares.
Answers to the second.:
I never said 10 sec. flat. I said 10-15 secs. to 150mph.
It was NOT a drag race, we were merely goofing around. No-one had a stop-watch. It was a while ago, so maybe my "memory's" faulty.
Seeing how uncommon Hemi's are it seems hard to believe you've been in that many. And I'm not sure what "muscle cars" you may have been in, but Hemi Super Bee is quite capable of reaching 150mph from a rolling start in 15 secs.
They were made for "superspeedways", not drag racing.
If you think muscle cars are not that fast you haven't been in a REAL one.
There are MANY muscle cars capable of 13's and 12's with very little work. And MOST were quicker than "14's" I don't know what you've been reading. The 427 Shelby Cobra held the record for something like 37 years for 0-100-0 in 13 secs.

 

Yep the 426 hemi - 425hp/490tq - used from '66-'71 in street cars usually yeilded 13-14 second quarter mile times. Cars used to be such pigs.

 

my 2 liter piston vs 426 hemi

 

Good photo!!!!! It put a good smile on my face.

Wes

 

Basically the combustion chamber was hemispherical with the spark plug placed in the middle. Chrysler tested different combustion chamber configurations in the 30s and found that the hemispherical chambers gave the best efficiency. Chysler had hemis back in the 30s btw but the largest displacement then was 392 Cu. in. When they decided to go racing in the 60s, they brought back the hemi chambers. The hemis werent without their problems though. The combustion chamber was a deep dome and to get good compression out of the engine, the piston had to have a very high dome. The ideal piston shape is a flat top so the dome wasn't the best. The large valve angle and close proximity of the valves also caused a lot of the mixture to go straight out the exhaust valve during the valve overlap period.

These problems were easily solved with supercharging though. The low compression meant a highly domed piston was no longer necessary and blower cams have no valve overlap. Supercharging really made the engines produce amazing power levels. Because of the centrally located spark plug, the flame front had less distance to travel before it reached the cylinder wall. This reduced the chance of detonation so more boost could be run than with a wedge type head.

The hemispherical combustion chamber evolved into the pent-roof chambers that are common on todays vehicles. The addition of squish pads increases fuel mixture turbulence, which further reduces detonation and allows higher compression ratios to be used. The only way to increase the thermodynamic efficiency of an engine is to increase the compression ratio. Therefore all combustion chamber research is dedicated to detonation reduction in order to increase compression ratios.

Alin

 

like everybody already said its a hemispherical design with the plug in the middle.. if you look at it from a side cut..it would look like a half circle..the placement of the plug gives it a real good and even burn when the mixture is ignited

 

A centrally located spark plug doesn't "give it a real good and even burn". Because the flame kernel is started at the center of the combustion chamber, the flame front has less distance to travel than if it started on the end like in a wedge head. As the flame front travels across the cc, the unburned end gasses are heated and compressed, which can cause them to spontaneously combust. That is detonation. With a centrally located spark plug, thse unburned end gasses are heated and compressed less, thereby reducing the chances of detonation and allowing a higher compression ratio to be used. And like stated above, the higher CR make the engine more thermodynamically efficient. It was all done to increase the efficiency of the engine. The mixture doesn't burn more "evenly" or even more "real goodly" than before.

Alin

 

To see a really overdone version of a hemi motor, look at a late 70'-early 80's Harley twin. The angle between the valves is around 90 degrees. To get compression up to around 8:1 they had to put a dome nearly as tall as the main part of the piston. I have not seen the heads from the new hemi, but I'll bet they are closer to a pentroof than an old hemi. I suspect they are similar to the Chevy big block head design. They must flow OK since the new 5.7 picked up 100 hp over their old 5.9.

BTW, the early Chrysler hemis were in the 50's not the 30's. In the 30's Chrysler was making flatheads. Fun trivia, the Ford model A used a flathead 4 cylinder with 4:1 compression in the late 20's, early 30's.

 

More fun engine trivia.The famous Ford V-8 flathead was produced from
1932 until well into the OHV era, Ford ceased production of it in 1953.
About the same time as Chrysler was experimenting with it's soon to be famous Hemis.
Just a couple more of my .02 cents

 

Who made the first 350 cid for passeneger cars?

 

isnt it true that most of our dohc 4 cyliners are in fact hemi based

 

Honda uses more of a pent roof style combustion chamber.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mista Bone &raquo;</TD></TR><TR><TD CLASS="quote">Who made the first 350 cid for passeneger cars?</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HOT ROD Magazine &raquo;</TD></TR><TR><TD CLASS="quote">Every month we get letters lambasting us for printing yet another 350 Chevy engine story. But we get even more asking for help building 350 Chevys. It’s been that way ever since 1967 when the first 350ci was introduced as an option only in the Camaro. </TD></TR></TABLE>

I love trivia

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mista Bone &raquo;</TD></TR><TR><TD CLASS="quote">Who made the first 350 cid for passeneger cars?</TD></TR></TABLE>
I can't quite remember,LOL too much junk in my head.
I'm 99% sure the first 350 cid was a chevy 350. in 1968 or '69
Can't remember when the ford 351 cleveland/windsor's came out.
But the evolution of the small block chevy started in 1953 or 1954 with 255 cid or 265? until the late '50s,Then 283cid, then 327 from the early to late '60's. Then it was upped to 400cid I think. And finally in '68 or '69 the dropped down to 350 where it stayed until now. ?? Do they still make a 350? Can't remeber LOL
And I agree I believe honda enginges are pent-roof heads.

 

well thanks for correcting me.... for me

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4crx4me &raquo;</TD></TR><TR><TD CLASS="quote">
Can't remember when the ford 351 cleveland/windsor's came out.</TD></TR></TABLE>

1969 if I remember correctly

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4crx4me &raquo;</TD></TR><TR><TD CLASS="quote">
But the evolution of the small block chevy started in 1953 or 1954 with 255 cid or 265? </TD></TR></TABLE>

I know it was the 265, but I forget the date. I think it was 1954.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4crx4me &raquo;</TD></TR><TR><TD CLASS="quote">Then it was upped to 400cid I think. And finally in '68 or '69 the dropped down to 350 where it stayed until now. ?? </TD></TR></TABLE>

in 1970, the 400 was released. The 350 chevy was never dropped, it was always in the line.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4crx4me &raquo;</TD></TR><TR><TD CLASS="quote">Do they still make a 350?</TD></TR></TABLE>

The LT1 (92-96 vettes, 93-97 f-bodies) was the last of the 350 base engine. The LT1 was computer controlled 350 (the castings were a little different from the old 350 and the head were completely different).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ProdriveWRC &raquo;</TD></TR><TR><TD CLASS="quote">Basically the combustion chamber was hemispherical with the spark plug placed in the middle. </TD></TR></TABLE>


Yeah an easy way to tell a hemi is look for the plugs on top of the valve covers. (kind of like our Hondas )

 

everybody has chevys on the brain, so sad........

Mopar Red Ram and Super Red Ram motors.


http://www.allpar.com/mopar/redram.html


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">The 'B' series wedge engine was introduced in 1958 with 350 and 361 cubic inch versions, followed a year later by the 413. It took several years and much experimentation for the new engine to establish a reputation</TD></TR></TABLE>

 

BUMP FOR KNOWLEDGE!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91wagonsir &raquo;</TD></TR><TR><TD CLASS="quote">BUMP FOR KNOWLEDGE!</TD></TR></TABLE>

There is enough in this post no reason to prolong the topic.

 

i heard that suburban's produced in the early 90's used 350 based engines. they get like 12 mpg