Hemispherical combustion chamber

A Hemi engine (from hemisphere) is an internal combustion engine in which the roof of each cylinder's combustion chambers is of hemispherical form.

History[link]

The 1903 Premier engine had a gear-driven overhead cam, roller cam followers, and crossflow hemi heads.

Hemispherical combustion chambers, which had been used for centuries in mortars and cannons,^[1] were introduced on some of the earliest automotive engines, shortly after proving the concept of internal combustion engines themselves.

Hemispherical cylinder heads have been used since at least 1901;^[2] they were used by the Belgian car maker Pipe in 1905,^[3] the Peugeot Grand Prix Car of 1912, the Alfa Romeo GP car of 1914, Daimler, and Riley. Stutz built four-valve engines, conceptually anticipating modern car engines. The BMW double push rod design, taken over by Bristol Cars, the Peugeot 403, the Toyota T engine and Harry Arminius Miller racing engines are other examples.^[4]

Technology and implementation[link]

With the hemispherical combustion chamber design, the intake and exhaust valves are on opposite sides of the chamber, sending the combustion mixture flowing directly across the chamber. This design is commonly referred to as a "cross-flow" head. Significant challenges in the commercialization of engines utilizing hemispherical chambers revolved around the design of the valve actuation, and how to make it effective, efficient, and reliable at an acceptable cost. This complexity was referenced early in Chrysler's development of their 1950s hemi engine: the head was referred to in company advertising as the Double Rocker head.^[3]

Benefits and drawbacks[link]

Although a wedge-head design offers simplified valve actuation, it usually does so by placing the valves side by side within the chamber. This can restrict the flow of the air/fuel mixture into and out of the chamber without a compensating design (including designs utilizing overhead cams). With a hemispherical chamber, a straighter flow path is provided for the air/fuel mixture across the chamber. Engineers have learned though, that just passing gas through a chamber quickly does not provide the best combustion event from an emissions, efficiency, or power perspective.

Drawbacks of the hemispherical chamber include increased production cost, high relative weight (25% heavier than a comparable wedge head per Chrysler's engineers^[5]), poor low-rpm performance characteristics and difficulty meeting emissions standards. These have pushed the hemi head out of favor in the modern era.

Usage[link]

Chrysler[link]

Perhaps the most widely known proponent of the hemispherical chamber design is the Chrysler Corporation. Chrysler became identified primarily by trademarking the "Hemi" name and then using it extensively in their advertising campaigns beginning in the 1960s. Chrysler has produced three generations of such engines: the first (the Chrysler FirePower engine) in the 1950s, the second (the 426 Hemi), developed for NASCAR in 1964 and produced through the early 1970s, and finally the "new HEMI" in the early 2000s. The "Hemi" engine introduced in 2002 by DaimlerChrysler had a combustion chamber featuring valve and twin spark plug locations markedly different from the second generation 426ci version. The current-production "Hemi" V8, with its pinched chamber, does not have true hemispherical combustion chambers despite the name; rather, it bears a closer resemblance to the mid-1950s polyspherical chamber, which Chrysler engineers developed as a lower-cost alternative head for their V8 engines. The polyspherical head needed less metal and was narrower due to using only one rocker shaft. This saved costs in material, space, and warranty claims and allowed it to be used in smaller vehicles. Chrysler's Australian-market Hemi-6 of 1970-80 had partial-spherical hemi chambers, though they were only 35% of a sphere.

Ford[link]

Ardun heads for the Ford flathead were perhaps the first use of a hemispherical head on a readily available American V8.^[6] First offered in 1947 as an aftermarket product, these heads converted the Ford flathead to overhead valves operating in a hemispherical chamber. Zora Arkus-Duntov, who later worked for GM and was a major force behind the development of the Chevrolet Corvette, and his brother Yura, were the "AR" "DUN" of "Ardun."

Ford produced an engine with two overhead cams (one cam per head) and hemispherical chambers in the mid-1960s. The engine, displacing 425 cu in (6,965 cc) and belonging to the FE family of Ford engines, was known as the "427 SOHC"; it was also known as the Cammer. It was basically a set of SOHC hemi heads that bolted onto Ford's FE engine block. The 1964 engine was designed in 90 days of intensive engineering effort^[7] for use in racing. The 427 SOHC used the side oiler engine block modified slightly to deal with the missing in-block cam among other OHC issues.^[7] Because of their power levels it was banned from NASCAR races, though allowed in certain drag racing classes. After the NASCAR ban, Ford continued to produce the SOHC, selling it over the counter to racers and others^[8] who used it to power many altered-wheelbase A/FX Mustangs and supercharged Top Fuel dragsters. Connie Kalitta, Pete Robinson, and "Snake" Prudhomme all used the engine in their Top Fuel racers. In 1967 Connie Kalitta's SOHC-powered "Bounty Hunter" won Top Fuel honors at AHRA, NHRA and NASCAR winter meets, becoming the only "triple crown" winner in drag racing history.^[9] Dynamometer results of the day showed the SOHC Hemi producing almost 700 hp (522 kW) in crate form (100 hp per liter).^[10] The overhead cams meant that it was not as rpm-limited as the Chrysler Hemis were with their pushrods and heavy and complex valvetrains.^[11]

Later Ford engine designs with hemispherical chambers included the Calliope, which used two in-block cams, arranged one over the other, to drive 3 valves per hemispherical chamber.^[12] The pushrods activating the valves from the top camshaft were almost horizontal. In 1968, Ford brought out a completely new engine family called the 385-series. This engine's heads used a modified form of the hemispherical chamber called Semi-Hemi.^[13]

In the 1970s, Ford designed and produced a small-block engine with hemispherical heads to address the growing concerns about fuel economy. Unfortunately, even with an ahead-of-its-time direct fuel injection system feeding a stratified charge chamber,^[14][15] the hemi's emissions could not be made clean enough for compliance with regulations. This plus the cost of the valve actuation systems, along with the cost of the high pressure pump needed to deliver fuel directly into the chamber, as well as the gilmer belt drive system needed to drive the pump, made further development pointless at the time. In 2007, taking advantage of the improvements in equipment, computer controls, and chamber design during the intervening years, Ford introduced its non-hemi Ecoboost line of direct-injected engines.

Aston Martin[link]

Aston Martin V8

Lotus Big Valve Head Hemi Chambers

Aston Martin's famous DOHC (4 cams) V8 used a hemispherical chamber during the late 1960s through the late 1980s. Each cam controlled one set of valves, either a bank of intake valves or a bank of exhaust valves. The Aston Martin V8 5.3 L (5340 cc/325 in³) produced 315 hp (235 kW).

Mitsubishi[link]

Mitsubishi produced several hemi engines including the 'Orion', 'Astron', and 'Saturn' units.

Alfa Romeo[link]

Alfa Romeo has produced many successful hemi-head engines throughout the years. Arguably one of their most beloved examples is Giuseppe Busso's original 2.5-liter V6, which has been cited by some as one of the best and most distinctive sounding production engines (even in its latter 24v forms) of all time.^[16] Part of this praise is likely because the hemispherical heads on the original 2-valve engine allowed for an almost completely straight exhaust port, resulting in a less diluted or muddied engine sound, allowing Alfa Romeo to use quieter stock exhausts without losing much of their distinct and beloved race-bred engine noise.

Porsche[link]

Porsche has made extensive use of hemi-head engines, including the air-cooled flat-6 engine in Porsche 911 models from 1963 to 1999. The 1973 2.7 L version generated 56 hp per naturally aspirated litre of piston displacement.^[17]

Jaguar[link]

Jaguar used this head design, beginning in 1949, on the legendary XK engines, which powered cars ranging from the Le Mans winning D-Type to the XJ6.^[18]

Lotus[link]

Lotus, along with many many other manufacturers, some of which are listed above, many others which are not, used hemispherical chambers in some of their engines (see photo to right). The relatively large valves possible in such a chamber allowed large volumes of air-fuel mixture to enter and exit the chamber quickly; not always completely combusted. In the modern emissions-era, the hemi chamber has begun to fade away from continuing development. The hemispherical combustion chamber is the simplest, and easiest design to understand. As such, it has served for more than a century as the basic design in combustion engines, from which all other improvements and engineering developments derive. As the engineering involved in new engines has improved and evolved, the true hemispherical chamber has morphed and twisted into more sophisticated and complex designs that are meant to extract more power, with lower emissions, from any given combustion event.

The hemi engine requires parts of more complexity and quantities. Upper photos of double rocker system for a pair of Hemi heads and its complex piston casting. Lower photos of comparable parts for a pair of Wedge Heads.

You get a Pentroof hemi chamber when you fit 4 flat-headed valves into a hemispherical space. Ford Windsor pentroof casting.

Supersession in modern engines[link]

Modern (2007) non-Hemi active combustion chamber

Current-production Chrysler "Hemi" combustion chamber

Many of today's engines use active combustion chambers designed to tumble and swirl the fuel/air mix within the chamber for the most efficient combustion event possible.^[19] These active chambers usually look like kidney beans or two merged small 'hemi' areas surrounded by flat quenching areas over the pistons.^[20] By the end of the 1970s, development of engines utilizing true hemispherical chambers had ceased around the world; it had been gradually displaced by dramatically improved newer engine designs. Today,"hemi" is more of a trademark than a description of a combustion chamber.

References[link]

Tim Allen
Allen in 2012
Birth name	Timothy Alan Dick
Born	(1953-06-13) June 13, 1953 (age 59) Denver, Colorado, U.S.
Medium	Stand-up, film, television, books
Nationality	American
Genres	Observational comedy, improvisational comedy, physical comedy, character comedy
Subject(s)	Relationships, marriage, masculinity, gender differences, parenting, everyday life
Spouse	Laura Deibel (1984–2003; 1 child) Jane Hajduk (2006–present; 1 child)
Notable works and roles	Tim Taylor on Home Improvement Mike on Last Man Standing Jason Nesmith in Galaxy Quest Scott Calvin/Santa Claus in The Santa Clause film series Buzz Lightyear in Toy Story film series
Website	http://www.timallen.com

Tim Allen (born Timothy Alan Dick;^[1][2] June 13, 1953) is an American comedian, actor, voice-over artist, and entertainer, known for his role in the sitcom Home Improvement. He is also known for his starring roles in several popular films, including the Toy Story film series, The Santa Clause film series, and Galaxy Quest.^[3][4] Allen currently stars in the ABC sitcom Last Man Standing.

Early life[link]

Born in Denver, Colorado, Allen is the son of Martha Katherine (née Fox), a community-service worker, and Gerald M. Dick, a real estate agent.^[3][5][6] He is the third oldest of five brothers. His father died in a car accident, colliding with a drunk driver, when Allen was 11.^[3][7] Two years later, his mother married her high school sweetheart, a successful business executive,^[5] and moved with her six children to Birmingham, Michigan, a suburb of Detroit, to be with her new husband and his three children.^[8] Allen attended Ernest W. Seaholm High School in Birmingham, where he was in theater and music classes (resulting in his love of classical piano). He then attended Central Michigan University and transferred to Western Michigan University in 1974.^[9] At Western Michigan, Allen worked at the student radio station WIDR and received a bachelor of science degree in communications specializing in radio and television production in 1976 with a split minor in philosophy and design.^[10] In 1998, Western Michigan awarded Allen an honorary fine arts degree and the Distinguished Alumni Award.^[9]

Career[link]

Allen started his career as a comedian in 1975.^[3] On a dare from one of his friends, he participated in a comedy night at a comedy club in Detroit. While in Detroit he began to get recognition appearing in local television commercials and appearing on cable comedy shows such as Gary Thison's Some Semblance of Sanity. He later moved to Los Angeles and became a member of The Comedy Store there. He began to do stand-up appearances on late-night talk shows and specials on record and film.^[3] Allen rose to fame in acting with the television series Home Improvement (1991–1999) on ABC, playing Tim "The Tool-Man" Taylor.^[3] During one week in November 1994, he simultaneously starred in the highest grossing film (The Santa Clause), topped the New York Times best-seller list with his book Don't Stand Too Close to a Naked Man, and appeared in the top rated television series (Home Improvement).^[3] The following year, he provided the voice of Buzz Lightyear in the blockbuster Toy Story.^[3] Simultaneous with his time acting in Home Improvement, Allen formed a race team with Steve Saleen and race driver Bob Bondurant, called the Saleen/Allen "RRR" Speedlab. The team raced Saleen Mustangs in the SCCA World Challenge, with Allen and Saleen as the team's drivers.

In 1997 he starred in the family comedy Jungle 2 Jungle from Disney. The film was poorly received by critics. The next year marked the final year of Home Improvement, for which he was paid $1.25 million per episode. The next year he returned to voice Buzz Lightyear in Toy Story 2 which was a financial and critical hit. Also in 2000 he starred in the sci-fi parody Galaxy Quest alongside Sigourney Weaver, Alan Rickman and Sam Rockwell. The movie was a critical hit and connected with audiences as well. In 2003 he had a cameo as Seann William Scott's father in American Wedding.

In 2006, Zoom was released, featuring Allen as Jack Shepard. The same year, he also starred in The Santa Clause 3 and The Shaggy Dog.

Allen began narrating the "Pure Michigan" television and radio commercials for the "Travel Michigan" agency. These commercials can be seen and heard throughout the Midwest and began airing nationally in 2009.

In December 2009, Allen started a preview tour of Crazy on the Outside, a film that debuted in January 2010. Allen accompanied the film, helping promote it with a series of stand-up acts beforehand. During the performances he told audiences that he plans a 2010 comedy tour. Allen also directed the film, marking his film directorial debut.^[11]

Allen with Jay Leno at the 45th Emmy Awards.

Allen hosted the 8th Annual TV Land Awards on April 25, 2010.^[12]

As of September 2010, Tim Allen is the official voice of the Chevrolet Cruze, narrating commercials for the vehicle. Also in September 2010, Allen was named the voice of Campbell Soup's new "It's Amazing What Soup Can Do" campaign.^[13]

As of 2011, Allen currently stars in the ABC sitcom Last Man Standing. He plays the role of Mike Baxter, a dad who is fighting for his manhood in his house filled with women.^[14]

Personal life[link]

On October 2, 1978, Allen was arrested in the Kalamazoo/Battle Creek International Airport for possession of over 650 grams (1.4 lb) of cocaine. He subsequently pleaded guilty to drug trafficking charges, and provided the names of other dealers in exchange for a sentence of three to seven years rather than a possible life imprisonment. He was paroled on June 12, 1981, after serving 2 years and 4 months in a Federal Correctional Institution, Sandstone in Sandstone, Minnesota.^[15][16][17] Allen had the Federal Bureau of Prisons Register # 04276-040.^[18]

Allen was raised as an Episcopalian.^[5] He was married to Laura Diebel from April 7, 1984, until they legally separated in 1999. Their divorce was finalized in 2003.^[19] They have a daughter, Katherine, born in 1989. Allen married actress Jane Hajduk on October 7, 2006, in a small private ceremony in Grand Lake, Colorado. They had dated for five years.^[20]

In 1997, Allen was arrested for DUI in Birmingham, Michigan, and was recorded as having a .15 percent blood-alcohol content.^[21] He was sentenced to one year probation. He entered a rehabilitation clinic for alcohol abuse as part of his court obligation.^[22]

On January 5, 2009, it was announced that Allen and Hajduk were expecting their first child together.^[23][24] On March 28, 2009, Allen's second child, a baby girl named Elizabeth, was born.^[25]

Awards[link]

Allen was nominated for one Emmy^[26] and 5 Golden Globe Awards. He won the Golden Globe Award for Best Actor – Television Series Musical or Comedy in 1995 for Home Improvement.^[27]

In 1999, Allen was named a Disney Legend for his work on the Toy Story and Santa Clause franchises.^[28]

In 1999 Allen won a TV Guide Award for Favorite Actor in a Comedy.^[29]

For contributions to the television industry, Tim Allen was honored with a star on the Hollywood Walk of Fame at 6898 Hollywood Blvd.^[30]

In 1996, he won the Hall of Fame award at the Kids Choice Awards.

The cast of Home Improvement was honored with a "Fan Favorite" award at the 2009 TV Land Awards.

Filmography[link]

Films[link]

Television[link]

Books[link]

• Don't Stand Too Close to a Naked Man (1994) – ISBN 0-7868-6134-7
• I'm Not Really Here (1996) – ISBN 0-7868-6257-2

References[link]

External links[link]

	United States portal
	Biography portal
	Film portal

Wikimedia Commons has media related to: Tim Allen

• Official website
• Tim Allen at the Internet Movie Database
• Tim Allen at AllRovi