Honda's Inline-Four Manifold Pipe Models: Birth and Expansion [Catalogs Reflect the Era: Part 18]

In December 1974, the "Dream CB400 FOUR" was released, featuring the world's first 4-into-1 exhaust system on a mass-produced motorcycle.

Affectionately known as "Yon-For" by motorcycle fans, it is a masterpiece that is still cherished by many enthusiasts over 50 years later.

It is no exaggeration to say that the birth of the Yon-For marked the beginning of the full-fledged history of so-called "collective mufflers" or "shūgōkan."

Let's look back at collective mufflers before the birth of the Yon-For.

1972 Yoshimura-tuned CB750 FOUR Racer

Commissioned by "Krauser," an American Honda dealer, Yoshimura Racing developed a CB750 racer equipped with a 4-into-1 collective exhaust system, in addition to engine tuning. At the time, many questioned this exhaust system, which overturned the common sense of two-wheeled vehicles. However, its high potential demonstrated at the 1972 Daytona 200 Miles race changed the world of racing.

#10 1972 Daytona 200 Miles Entry CB750 Racer (Yoshimura Krauser Honda) #15 1973 Daytona 200 Miles Entry CB750 Racer (At Honda Collection Hall in 2025)

The CB750 racer was equipped with a 4-into-1 muffler and achieved 6th place with rider Morio Sumitani.

While the 4-into-1 system gradually gained traction in the world of road racing, its practical application in production motorcycles faced numerous hurdles, including noise levels, ease of use in urban areas, balance with the chassis, and styling considerations.

1974 Birth of the Dream CB400 FOUR

The Dream CB400 FOUR, released in December of that year, featured a sleek and beautiful collective exhaust system that was both innovative and elegant.

The Yon-For was developed as a successor to the Dream CB350 FOUR, which also featured a four-cylinder engine. For the exhaust system, Honda challenged the development of a collective type that would be lighter and potentially more cost-effective than the 350's four separate mufflers. With the cooperation of muffler manufacturer Sankei Giken Kogyo, they succeeded in creating an exhaust system that captivated onlookers.

※The catalog is privately owned, so please excuse any dirt or discoloration.

Catalog cover produced in March 1975. The 4-into-1 exhaust system is the main feature.

The slogan "You are the wind." left a fresh and powerful impression.

The body colors were Light Ruby Red and...

...and Varnish Blue.

Introducing the features of the 4-into-1 system. ...

...achieving both increased output and silencing effect.

The air-cooled inline-four engine and...

...a page emphasizing the 4-into-1 system.

Page 4 appears to discuss the high-quality ball joints used in the backstep and shift linkage.

Second Wave: CB750 FOUR and CB550 FOUR

In June 1975, the CB750 FOUR-II and CB550 FOUR-II were released as the second wave of 4-into-1 muffler models.

Issued June 1975. The cover of the CB750 FOUR-II features the 4-into-1 logo.

This is a standard angle for collective muffler models.

The usefulness of the exhaust system...

...is explained on this page.

The yellow body color stands out against the blue sky. Yellow is a color of adventure.

Equipped with disc brakes on both front and rear wheels, ...

...improving safety.

In this era, many catalogs featured...

...three-view drawings.

The body colors were yellow and red.

Due to its luxurious equipment, the CB750 FOUR-II was priced ¥73,000 higher than the concurrently sold CB750 FOUR with four mufflers.

Issued June 1975. The cover of the CB550 FOUR-II inherits the gentle image.

The slogan "The quiet man" from the CB500 FOUR is carried over.

The tank features the SUPER SPORT logo, same as the CB400 FOUR and CB750 FOUR-II.

The exhaust pipes are designed with...

...a beautiful curve.

Explanations of each part are presented using many photos...

...making for an easy-to-understand layout.

The colors are black and blue. The price is ¥398,000. The 4-into-1 models are unified in solid colors.

The CB550 FOUR-II, while reflecting the styling of the CB400 FOUR, did not gain widespread support from users.

Four months after its release, the CB550 FOUR was released with minor changes, suggesting that many users at the time still preferred four mufflers. This model, along with the CB550 FOUR, became the last in the CB550 FOUR series.

CB550 FOUR released October 1975 (4 mufflers)

The Later Years of the CB750 FOUR-II

Due to a lukewarm reception from users for the 1975 model, a change to a sportier model was planned.

In April 1977, the new CB750 FOUR-II was announced.

Cover of the CB750 FOUR-II issued June 1977.

The front and rear wheels are equipped with Honda's unique Comstar wheels. The muffler has been updated to a megaphone type, giving it a powerful styling befitting a 750.

The CB750 FOUR with four mufflers also underwent minor changes and was released concurrently with the new CB750 FOUR-II. This indicates that many CB fans at the time preferred the four-muffler setup.

These two models were the last in the OHC four-cylinder CB750 FOUR series.

CB750 FOUR released April 1977 (4 mufflers)

The CB750 FOUR evolved into the CB750F, released in June 1979.

The engine was updated from OHC to DOHC.

The exhaust system became a dual muffler, although still a collective type, and the 4-into-1 system disappeared.

From the catalog issued April 1980. The highly successful CB750F.

Return of the Inline-4 Collective Muffler with the CBR

In December 1983, the CBR400F was born as the first model under the product brand "CBR."

The high-performance DOHC 4-valve inline-four engine featured a 4-2-1-2 collective exhaust system with dual mufflers.

CBR400F from the catalog issued December 1983.

The CBR400F was successful in production racing and gained popularity as a super sport model incorporating Honda's racing technology.

Then, in August 1985, the CBR400F, CBR400F Endurance, and CBR400F Formula 3 were simultaneously announced with model changes. These three models adopted a 4-into-1 exhaust system.

Ten years after the release of the CB400 FOUR in December 1974, the collective muffler made a comeback in the 400cc class.

Since then, the CBR series has actively adopted the 4-into-1 exhaust system.

CBR400F Endurance released August 1985 (model with half cowl).

CB Reborn with the CB-1

In March 1989, the CB-1 was released as a pioneer of naked styling, featuring a water-cooled DOHC 4-valve inline-four engine. The exhaust system was a 4-into-1 system.

CB-1 released March 1989.

The 4-into-1 system was subsequently adopted in models such as the CB400 Super Four and CB1000 Super Four, becoming long-selling models supported by many riders.

While exhaust system preferences vary from person to person, the collective muffler, a staple item for inline-four supersport models, owes its current prevalence to the ideas and challenges of Yoshimura Japan, and its success in mass-produced vehicles with the CB400 FOUR.

1974 CB400 FOUR

2026 CB400SF E-Clutch

Side Story: Twin-Cylinder Collective Muffler CJ

In April 1976, based on the twin-cylinder CB250T and CB360T, the CJ250T and CJ360T were released, featuring a 2-into-1 system.

The CJ adopted a cafe racer style, with a resin front fender and a compartment box (rear cowl) behind the seat.

To reduce weight, the starter motor was removed, but the vehicle weight of both the 250 and 360 was 2kg heavier than the CB.

The transmission was changed from the CB's 6-speed to a 5-speed, prioritizing ease of use in urban areas.

The price was over ¥10,000 higher than the CB, resulting in sluggish sales.

The environment surrounding the motorcycle industry at the time was deteriorating due to incidents involving "bosozoku" (biker gangs).

Parts essential for the cafe racer style, such as flat handlebars (or semi-up handlebars) and backsteps, were difficult to obtain approval from administrative agencies.

Reflecting these circumstances, the CJ250T and CJ360T were short-lived models.

Issued 1976. CJ250T/360T and...

...from the CB250T/360T catalog.

The CJ's color scheme was solid yellow and red, inspired by the CB400 FOUR. Solid colors at the time were perceived as inexpensive.

Introduction page for CB250T/360T.

The CB series, with its tank stripes, upward-swept mufflers, and chrome fenders, evokes the tradition of the CB and provides a sense of security.

The cafe racer style promoted by manufacturers in the 1970s shows evidence of difficult choices made in consideration of the social climate.

(End)