RE: PH Origins: The 'Hemi' combustion chamber

RE: PH Origins: The 'Hemi' combustion chamber

Monday 22nd October 2018

PH Origins: The 'Hemi' combustion chamber

The quest for more power led to the development of the hemispherical combustion chamber decades before Chrysler arrived



Say 'Hemi' and the first company that will undoubtedly enter most enthusiasts' minds is 'Chrysler'. That won't surprise many, given that the American manufacturer has built a substantial brand around that four-letter word - and one based on a long-standing legacy of high-performance engines for both consumer and motorsports applications.

Chrysler's first production hemispherical-headed V8, for example, arrived in late 1950. The 5.4-litre 'Firepower' V8 initially cranked out 180hp and 312lb ft, figures that would be sneered upon by the horsepower per litre brigade today. Back then, though, that was a pretty stout output - and higher than many a rival.

Things had improved considerably by the time this first generation of hemi-headed motor was drawing to a close, though; the 1958 '392' displaced 6.4 litres and thundered out 390hp and 435lb ft. This was thanks in part to an early, albeit finickity, electronic fuel injection system called the 'Electrojector'.


Chrysler launched the second generation in 1964 and, this time, the engine was formally branded 'Hemi'. This line consisted solely of the now-legendary 7.0-litre '426', which today still features prominently in NHRA drag racing and other motorsports classes - although it often bears little resemblance to anything offered back then.

In 2003, the 'Gen 3' Hemis arrived. The combustion chamber of these was substantially different from the fabled hemispherical design of their predecessors, though, making them more Hemi by association than design. Nevertheless, these engines are still often held in high regard. Justifiably so, given that the likes of the supercharged 6.2-litre Hemi in the Dodge Challenger SRT Hellcat Redeye pounds out 797hp and 707lb ft.

However, Chrysler's history with hemispherically shaped combustion chambers begins before all of this - and dates back to development projects prior to America's entry into World War II. Back then, Chrysler was reportedly studying ways to cut carbon deposits in combustion chambers. These carbon deposits, once they started accumulating, would gradually cause a reduction in efficiency.


During these studies, Chrysler found that a bowl-shaped hemispherical combustion chambers resisted the accumulation of carbon deposits. The design also had other advantages, compared to conventional wedge, bathtub and heart-shaped combustion chambers.

In particular, the cross-flow layout of the valves, and the angle at which they were mounted, improved gas flow in and out of the cylinder. This, in conjunction with the ability to fit larger valves in a hemispherical chamber, boosted the volumetric efficiency of the cylinder considerably.

The design also meant that the spark plug could be located in a far better position, granting improved combustion - which no doubt contributed to the reduction in carbon build-up - and the design was also more thermally efficient. All in, the hemispherical combustion chamber was one that offered good potential power and reliability. There were some downsides, mind, including large cylinder heads - due to the angle of the valves - which induced weight and packaging issues.


It's worth noting that, by this point, the more modern and capable four-valve 'pent-roof' combustion chamber design was also around. Nevertheless, Chrysler persisted with research into the hemispherical chambers and this experience culminated in the production of the prototype 'XIV-2220' of 1945. This force-fed inverted V16 aero engine, which displaced 36.4 litres, was initially planned to produce 2,500hp. Reputedly, the engine used both supercharging and turbocharging - like some others from the era - and went on to develop upwards of 3,000hp during trials.

The development of that engine was ultimately curtailed by both the end of the war and the start of the jet era. That all said, though, the concept of the hemispherical combustion chamber dates back even further than Chrysler's developmental work.

In the early days of the internal combustion engine, getting a good fuel-air charge into a cylinder and burning it effectively was proving difficult. Early combustion chamber designs were often inefficient and the valves small, restricting performance. This, for one thing, is what spurred many engineers to begin working on forced induction systems right from the outset.


This was a particular problem if you wanted a light engine that produced a good amount of power. This was proving a particular hurdle for those developing the first powered aircraft, such as oft-overlooked innovator Augustus Herring. The American engineer, who was born in 1867, was one of the pioneers of powered flight - but he was struggling to find suitable powerplants for his airframes.

Herring was undoubtedly fascinated by engine technology, aviation work aside, and contributed to numerous issues of 'The Horseless age' - a magazine founded in 1895 that charted and explored the ever-developing automotive marketplace. In it he wrote frequently on matters of engine efficiency, balance and commonly encountered issues.

This interest and expertise led to Herring developing his own engine in order to come up with something of an appropriate weight and output. In doing so, he is claimed to have designed an experimental hemispherical head in 1897. The was then used in a prototype petrol two-cylinder overhead cam engine - albeit one with a single valve per cylinder and exhaust ports near bottom-dead centre.


Herring then worked for the Truscott Boat Manufacturing Company in 1898, where the concept of hemispherical cylinder heads was seemingly advanced further - because, in 1901, Truscott itself unveiled a prototype two-cylinder, hemi-headed engine with two valves per cylinder. Other versions would soon follow.

Herring would also produce other engines using this design, including a single-cylinder variant that ran in 1902 - along with other innovations, covered in C. David Gierke's excellent two-part book 'To Caress the Air: Augustus Herring and the Dawn of Flight'.

Other engineers seemingly took note and, before long, hemi-headed engines were popping up all over the place, such as that found in the 1903 Premier racer - which had a four-cylinder, air-cooled 15-litre hemi that produced 100hp. Belgian manufacturer Pipe adopted the concept in 1905, too, as did the Welch Motor Car Company - which produced four- and six-cylinder engines, equipped with hemispherical combustion chambers, before the company was bought by General Motors in 1909.

The design would continue to be used for decades to come, by numerous manufacturers, and - when finally branded 'Hemi' in Chrysler's high-performance applications - it would go on to become one of the most recognised types of engine in existence. As the advertising and well-established saying goes, 'That thing got a Hemi?'

Author
Discussion

Lowtimer

Original Poster:

4,014 posts

107 months

Monday 22nd October 2018
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Seriously? Doing a piece on the history of the hemispherical combustion chamber and not mentioning the Jaguar XK?!

Omega1987

23 posts

11 months

Monday 22nd October 2018
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My Moto Guzzi also uses Hemi heads, supposedly for efficency which it certainly does well.

TooMany2cvs

29,008 posts

65 months

Monday 22nd October 2018
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Just shows how good Chrysler's marketing was, that anybody EVER thought they were in any way innovative...

Not one bit of it - it was just that the other yank v8s were and are about as technologically sophisticated as a dinosaur.

(and 1948 wasn't just the year the XK six was launched with hemispherical combustion chambers - the 2cv's flat twin, too.)

unsprung

2,677 posts

63 months

Monday 22nd October 2018
quotequote all
TooMany2cvs said:
Just shows how good Chrysler's marketing was, that anybody EVER thought they were in any way innovative...

Not one bit of it - it was just that the other yank v8s were and are about as technologically sophisticated as a dinosaur.

(and 1948 wasn't just the year the XK six was launched with hemispherical combustion chambers - the 2cv's flat twin, too.)
hooray! splendid indeed

British Drag Racing Hall of Fame honors the Chrysler Hemi V-8
https://www.hemmings.com/blog/2015/12/02/british-d...


Strugs

449 posts

168 months

Monday 22nd October 2018
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Let's not forget Turner's 2.5 litre V8 Daimler engine..
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Mound Dawg

1,868 posts

113 months

Monday 22nd October 2018
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TooMany2cvs said:
Just shows how good Chrysler's marketing was, that anybody EVER thought they were in any way innovative...

Not one bit of it - it was just that the other yank v8s were and are about as technologically sophisticated as a dinosaur.

(and 1948 wasn't just the year the XK six was launched with hemispherical combustion chambers - the 2cv's flat twin, too.)
Alfa engines had hemi heads from the late 20s/early 30s. The immortal twincam has them too-

https://www.alfaholics.com/race-parts/105-series/e...

CDP

5,605 posts

193 months

Monday 22nd October 2018
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My father had a 1927 Ballot LTS with an overhead cam and hemispherical combustion chambers.

donkmeister

1,434 posts

39 months

Monday 22nd October 2018
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Strugs said:
Let's not forget Turner's 2.5 litre V8 Daimler engine..
And it's 4.6 litre "450" brother. Marvelous engines.

rockin

6,227 posts

184 months

Monday 22nd October 2018
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If this hemi thread flots your boat, just wait 'til they get to "twin-spark"! smile

Nitro666

14 posts

85 months

Monday 22nd October 2018
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Yes, Britain’s own mini Hemi, Daimler’s 155cui V8. Incredible engine. Just look up Russ Carpenter’s “Glacier Grenade” or Robin Read’s “Bad Habbit”. I think both ran 6 second quarter miles.

v8250

2,612 posts

150 months

Monday 22nd October 2018
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Who wrote this article? Many paragraphs and not a single mention of the great British engineer, Edward Turner

https://en.wikipedia.org/wiki/Edward_Turner

Lewis Kingston

208 posts

16 months

Monday 22nd October 2018
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v8250 said:
Who wrote this article? Many paragraphs and not a single mention of the great British engineer, Edward Turner
I did – but, as the title suggests, these focus on the origin of the concept or technology at hand. I generally try to avoid them simply becoming lists of everyone who has later used or developed similar (countless companies in this case - including Jaguar, Daimler, Ford, Alfa, Toyota, Peugeot, BMW, etc.). smile

Rest assured, though, when it comes to doing a piece on hemi-headed V8s, he'd be in there. Always loved those Daimler engines. Fancy building a 2.5 on ITBs at some point...

Edited by Lewis Kingston on Monday 22 October 21:50

Strugs

449 posts

168 months

Monday 22nd October 2018
quotequote all
Nitro666 said:
Yes, Britain’s own mini Hemi, Daimler’s 155cui V8. Incredible engine. Just look up Russ Carpenter’s “Glacier Grenade” or Robin Read’s “Bad Habbit”. I think both ran 6 second quarter miles.
Russ has just rebuilt the engine in our 1966 Daimler V8 saloon. His dragster is in the workshop there. 1000bhp back in the day. He smiled when I asked whether, technically, his dragster engine could be made to fit our car.. biggrin

NFC 85 Vette

2,344 posts

175 months

Tuesday 23rd October 2018
quotequote all
TooMany2cvs said:
Just shows how good Chrysler's marketing was, that anybody EVER thought they were in any way innovative...

Not one bit of it - it was just that the other yank v8s were and are about as technologically sophisticated as a dinosaur.

(and 1948 wasn't just the year the XK six was launched with hemispherical combustion chambers - the 2cv's flat twin, too.)
While they're deemed technologically prehistoric, it's difficult to dispute that when it comes to producing horsepower, they're still ahead of the competition. The article mentioned that in current competition, they bare little resemblance to the original elephant motor - in truth the bulk of the changes centre around materials that were improved over the years to give more durability and oil galleries repositioned; the OEM architecture remains largely the same, it's just bits were beefed up for competition. Valvetrain geometry gets tinkered with in certain applications (the Pro Mod and TM alky heads have altered valve angles etc).

Chevy and Ford could produce good amounts of power back in the day, but when nitro racing became a business rather than a sport, the necessity for between rounds maintenance led toward adopting the Mopar way of doing things as they're just easier to strip down and rebuild if you're on a clock.

If you were take an iron World Products block, iron 426 heads and stock valve gear, you could still make an honest 2000 horsepower with relatively little spend. In racing though, we need more durability, and the advent of billet blocks, heads and cranks allows to run motors harder, to the tune of something between 3000-4000 horsepower in an application such as Nostalgia Funny Car, or up to 11,000 horsepower in big show fuel classes. Not bad for a dinosaur with a camshaft in block, 16 valves and some push rods thumbup

TooMany2cvs

29,008 posts

65 months

Tuesday 23rd October 2018
quotequote all
NFC 85 Vette said:
While they're deemed technologically prehistoric, it's difficult to dispute that when it comes to producing horsepower, they're still ahead of the competition.
Only because they're big.
Specific power is lousy.

NFC 85 Vette said:
If you were take an iron World Products block, iron 426 heads and stock valve gear, you could still make an honest 2000 horsepower with relatively little spend.
Mmm. Meanwhile, in real life showrooms, the 5.3 v8 in a brand new 2019 Chev Tahoe puts out 355bhp and 383lbft. Or you could have a 6.2 v8 with 420bhp and 460lbft.

That's roughly 67bhp/73lbft per litre from each. Woo. Hoo.

NFC 85 Vette

2,344 posts

175 months

Tuesday 23rd October 2018
quotequote all
TooMany2cvs said:
NFC 85 Vette said:
While they're deemed technologically prehistoric, it's difficult to dispute that when it comes to producing horsepower, they're still ahead of the competition.
Only because they're big.
Specific power is lousy.
What's the definition of big? You might have 800ci mountain motor nitrous engines, and 526ci blown pro mods, but the engine I built for the Corvette displaces 411ci (6.85 litres - so it isn't massive in the grand scheme of things) and will produce something in the region of 3500bhp in its base tune (probably closer to 4000bhp with some planned upgrades to ensure it's competitive). I thought that was pretty decent with a 6/71 roots blower, mechanical fuel injection and a single points magneto.

PorkRind

2,761 posts

144 months

Tuesday 23rd October 2018
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Interesting article. Thanks.

TooMany2cvs

29,008 posts

65 months

Tuesday 23rd October 2018
quotequote all
NFC 85 Vette said:
What's the definition of big?

(6.85 litres - so it isn't massive in the grand scheme of things)
Riiiight.

irocfan

18,605 posts

129 months

Tuesday 23rd October 2018
quotequote all
TooMany2cvs said:
NFC 85 Vette said:
While they're deemed technologically prehistoric, it's difficult to dispute that when it comes to producing horsepower, they're still ahead of the competition.
Only because they're big.
Specific power is lousy.

NFC 85 Vette said:
If you were take an iron World Products block, iron 426 heads and stock valve gear, you could still make an honest 2000 horsepower with relatively little spend.
Mmm. Meanwhile, in real life showrooms, the 5.3 v8 in a brand new 2019 Chev Tahoe puts out 355bhp and 383lbft. Or you could have a 6.2 v8 with 420bhp and 460lbft.

That's roughly 67bhp/73lbft per litre from each. Woo. Hoo.
Who gives a st about hp/cc? The SBC is the world's most popular engine and lasts quite well despite abuse. Repair costs are, relatively, cheap as chips thanks to the ability to chunter along at 1800rpm @ 75mph and then push to forward in a most entertaining manner if called upon to do so. KISS, great principles

TooMany2cvs

29,008 posts

65 months

Tuesday 23rd October 2018
quotequote all
irocfan said:
Who gives a st about hp/cc?
Here in the real world, anybody with a smidgin of basic common sense - not least because it's a fairly fundamental clue as to basic efficiency.

irocfan said:
The SBC is the world's most popular engine
Debatable, unless you struggle to comprehend that "the world" exists past the borders of the US. 'course, that also ignores the myriad of quite wide-ranging changes made to the small block family across 50 years of production.

Even if it is true, surely the fact that there were apparently no significant technical advances between the mid 50s and the early 00s is not particularly laudable?