A 400 on Steroids: Suzuki GS450

By Motorcycle Classics Staff
Published on February 13, 2014
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In Japan, 400cc bikes are popular because they classify as “medium” size; go bigger than 400cc and you’re in a more expensive tax class. But that line in the sand doesn’t apply in the U.S., so Suzuki gave its little twin a cc boost to make it more appealing to U.S. buyers. The Suzuki GS450 was really a 400 on steroids. Though it used the same format as the 1976-1979 GS400 and the interim GS425, the GS450 engine was new from the crank up.
In Japan, 400cc bikes are popular because they classify as “medium” size; go bigger than 400cc and you’re in a more expensive tax class. But that line in the sand doesn’t apply in the U.S., so Suzuki gave its little twin a cc boost to make it more appealing to U.S. buyers. The Suzuki GS450 was really a 400 on steroids. Though it used the same format as the 1976-1979 GS400 and the interim GS425, the GS450 engine was new from the crank up.
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Honda tuned the CB400 engine for midrange torque, courtesy of its “power chamber” exhaust collector box, but it still turned in a respectable 14.3-second quarter-mile run at 91mph. And on the road, Cycle magazine found it to be “one of the best handling motorcycles available today,” with “light, precise and responsive steering.” Cycle’s gripes were limited to noticeable driveline lash, a fade-prone front brake, vibration at high revs and cheap stiction-prone fork seals. They also noted a few missing conveniences, including the lack of an integrated steering lock and no self-canceling turn signals. Summing up its impressions, Cycle Guide called the CB400T, “a bike that answers your commands instantly and zings around corners with speed that will be the envy of 750cc riders.”
Honda tuned the CB400 engine for midrange torque, courtesy of its “power chamber” exhaust collector box, but it still turned in a respectable 14.3-second quarter-mile run at 91mph. And on the road, Cycle magazine found it to be “one of the best handling motorcycles available today,” with “light, precise and responsive steering.” Cycle’s gripes were limited to noticeable driveline lash, a fade-prone front brake, vibration at high revs and cheap stiction-prone fork seals. They also noted a few missing conveniences, including the lack of an integrated steering lock and no self-canceling turn signals. Summing up its impressions, Cycle Guide called the CB400T, “a bike that answers your commands instantly and zings around corners with speed that will be the envy of 750cc riders.”
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At first pass, the Yamaha Seca 400’s spec sheet reads a lot like the GS450: an air-cooled, double overhead cam, 2-valve, 180-degree parallel twin with counterbalance shaft, 34mm Mikuni CV carbs, transistor ignition, gear primary, six speeds, 14.1-second standing quarter at 92mph, braking from 30mph in 32 feet and a 100mph top speed.
At first pass, the Yamaha Seca 400’s spec sheet reads a lot like the GS450: an air-cooled, double overhead cam, 2-valve, 180-degree parallel twin with counterbalance shaft, 34mm Mikuni CV carbs, transistor ignition, gear primary, six speeds, 14.1-second standing quarter at 92mph, braking from 30mph in 32 feet and a 100mph top speed.

Suzuki GS450ET/ST
Claimed power:
38hp @ 9,500rpm (measured at the rear wheel)
Top Speed: 100mph
Engine: 448cc air-cooled, DOHC parallel twin
Weight (dry): 386lb
Fuel capacity/MPG: 55-50mpg
Price then/now: $1,739 (ST), $1,659 (ET)/$700-$1,500

The Suzuki GS450 was really a 400 on steroids. In Japan, 400cc bikes are popular because they classify as “medium” size; go bigger than 400cc and you’re in a more expensive tax class. But that line in the sand doesn’t apply in the U.S., so Suzuki gave its little twin a cc boost to make it more appealing to U.S. buyers.

Though it used the same format as the 1976-1979 GS400 and the interim GS425, the GS450 engine was new from the crank up. The 180-degree crankshaft was now one piece (it was built-up on the 400 and 425), and ran on three automotive-style plain bearings instead of balls and rollers as before. The bore was stretched from 67mm to 71mm, while stroke was shortened from 60mm to 56.6mm.

Beyond that, the GS450 engine was just like earlier versions. A single self-adjusting chain spun two overhead camshafts, which in turn operated two valves per cylinder, with a 36mm intake and 30mm exhaust. A revised gear-driven engine counter-balancer quelled primary vibration and rocking forces, and helical primary gears drove a wet multiplate clutch and 6-speed gearbox with chain final drive. Two 34mm constant velocity Mikuni carbs fed the combustion chambers, fired by transistorized electronic ignition.

The drivetrain slotted into a dual-downtube steel tube cradle frame with hydraulic front forks and swingarm rear suspension with preload adjustable shocks. A single-disc front brake and rear drum provided stopping. The package was available as the naked GS450ET or the sportier GS450ST with a handlebar-mounted quarter fairing; Suzuki called the GS450ST their “little café” in period ads. A cruiser-style GS450L rounded out the 450 lineup.

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