Suzuki GT550

The Suzuki GT550 is a two-stroke, air-cooled, three cylinder 1970s-era motorcycle in Suzuki's "Grand Touring" GT series. Even though total production of the 550 exceeded 60,000 examples spread over a six model year production run, this total was exceeded by both of its three-cylinder GT series brothers. Suzuki produced over 80,000 units of the GT750 and over 100,000 units of the GT380. All three models were originally offered for sale with the beginning of the 1972 model year (MY) with the 550 called "Indy" for the North American market. Production of the 550 was delayed because it was not available to dealers in the US until after April, 1972. In Suzuki's numbering scheme, automobile race tracks identify each of its 3-cylinder GT bikes for the North America market: 380 for Sebring, 550 for Indy, 750 for Le Mans.

Due to poor styling, high weight, poor ground clearance, a relatively low top speed and economical pricing the GT550 was more of a commuting and touring bike than a racer, despite its racetrack-derived name.

The 550 (and the 380 ) have a ram-air cooling system for the one-piece cylinder head. Two-stroke engines lose power after the engine reaches its critical temperature, so Suzuki used a system from its 500 cc two stroke twin cylinder racer, the T500.

This system consisted of a two piece aluminum shroud bolted to the cylinder head to duct ambient air over the cylinder head finning. The centre part of the head had an increased fin area and a larger shroud entry area in an effort to keep the centre cylinder running at the same temperature as the naturally more exposed outboard cylinders.

Suzuki Recycle Injection System (SRIS) was the first attempt by anyone to reduce visible emissions from a two stroke motorcycle. It was a small check valve in the bottom of each crank chamber. Two stroke engines have a tendency to collect unburnt oil and fuel in the bottom of the crank chamber at idle. Upon acceleration, after a period of idling, the unburned oil and fuel gets sucked up the transfer ports and contributes to an overrich mixture for the first 5 to 10 seconds resulting in a smokescreen from the exhaust. The SRIS plumbing routed the unburned fuel and oil to the next cylinder in the firing order thus allowing it to mix more thoroughly with the incoming charge of that cylinder and lowering the production of visible smoke. Overall fuel and oil consumption was unchanged but visible smoke was greatly reduced on sudden acceleration from rest.

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