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Brilliant Biking Inventions – Twin Swirl Combustion Chambers (TSCC)

Yes we love our classics here at CB-Net, but you may be surprised to learn that the ol’ acronym TSCC has been seen on a range of bikes as new as Suzuki’s SV650S, a raft of Suzuki GSX-Rs, through to dirt bikes like the DRZ400S and the cruiser GN250…

But where did TSCC come from? Well, we mentioned a little while back that the legendary Keith Duckworth who was behind the majority of the design of the Cosworth DFV F1 V8 engine had looked at the mighty Rolls Royce Merlin engine that powered the Supermarine Spitfire of World War II. Some of the ideas he found in the aero engine he put into the DFV which won first time out at Zandvoort in the hands of Jim Clark in his Colin Chapman-designed Lotus 49.

As we mentioned before, the likes of Suzuki had studied both the DFV and the Merlin and in the late 1970s (at a time when the DFV derivatives were still winning in F1) Suzuki engineer Sadao Shirasagi was given the job of improving the firm’s range of GS750 and GS1000 engines for a new range of motorcycles. What he came up with – TSCC – did owe a fair amount to the DFV…

Shirasagi-san knew that the DFV’s four-valve per cylinder layout was the way ahead for the up-coming GSX1100 (GS1100 in the United States) but he also wanted to improve the engine’s fuel consumption and performance across the rev-range, so actually improving efficiency as well as increasing the fuel/air flow with more valves was the goal for both him and the team at Suzuki.

The way to get more oomph from your fuel charge, was to get better fuel aeration and distribution in the combustion chambers. The original Twin Swirl Combustion Chamber featured a longitudinal ridge in the roof of the chamber, intersected by the spark plug, which effectively divided the chamber in two, funnelling the intake charge into what is now two, small domed chambers in a controlled circular ‘swirl’ rather than a more random turbulence that you would get in one large chamber. As the piston rose on the compression stroke, a V-shaped squish area located between each set of valves accelerates the ‘swirl’ effect. The chamber itself was also small and shallow, allowing the use of a flat-topped piston with the associated higher compression ratio this would allow.

So it proved that TSCC promoted even distribution of the fuel, which – allied to the overall design of the combustion chamber itself – permitted a higher compression ratio without the worry of pre-ignition. The central spark plug also ensured an even-burn of the intake charge, hence giving more complete combustion. Meanwhile the included angle between the GSX1100’s valves of 40 degrees meant they were located closer to a point right above the combustion chamber, allowing a smoother shape for the intake port, as the valve guides didn’t intrude into the port itself.

Suzuki was quick to patent their take on the idea – even if many similar designs (including the DFV’s) were around at the time. On 1980’s GSX1100E, TSCC gave better fuel efficiency and cleaner burn at both low and high revs and therefore improved throttle response into the bargain. The motor has since become a legend in classic circles…

As technology developed, so did TSCC. By 1983 when the GSX-R750 was on the drawing board, many tuners were coming to terms with the limitations of the original TSCC design. Some were cutting chamfers into the top of the cylinder at the four corners of the combustion chamber. The idea was to increase the spread of combustion and reduce detonation. In the GSX-R750, TSCC was made more compact being completely within the cylinder bore, and equipped with larger valves compared to the out-going GSX750. Air was fed by the eight-litre air-box under the tank as part of the DAIS or ‘Direct Air Intake System.

When the 750J Slingshot arrived, mods were made to the TSCC to give even better combustion with the larger valves of the new motor. With the introduction of the water-cooled WN in 1992, a more compact combustion chamber with smoother intake ports to minimize turbulence was debuted.

With TSCC going on to be seen in a number of different motors from Suzuki alone, it’s little wonder that we rate it as a Brilliant Biking Invention!