Sequential turbo5/30/2023 Sequential turbocharging requires all sorts of convoluted plumbing and valving to manage the path of exhaust gasses. It's almost as if there's a momentary flat-spot in power delivery, then wham! Off to the races. You wouldn’t call them super laggy, but the introduction of the second turbocharger is never 100-percent seamless. At the time, these setups were a huge technological step forward, and we were extremely impressed at the time, but by today's standards, sequentially turbocharged cars feel odd. So, does sequential turbocharging work? Yes and no. All these systems use the same basic principle as the 959-exhaust gasses are routed to one turbocharger at low RPMs, then around 4000 rpm some of those gasses are diverted to a second turbocharger. The most famous sequential-turbo equipped Japanese car, though, is the Toyota Supra, with its twin-turbo 2JZ-GTE. Subaru did the same with various (mostly JDM) Legacy models. It did not copy the 959's sequential turbocharging, though the GT-R drew lots of inspiration from Porsche's variable all-wheel drive system.) Mazda went with sequential turbochargers for the third-generation RX-7 and in the three-rotor Eunos Cosmo. (Fun aside: Nissan actually bought a 959 for benchmarking while it was developing the R32-generation Skyline GT-R. The late Eighties was the bubble era in Japan, when automakers had practically unlimited budgets to engineer whatever the hell they wanted. The 959 proved influential, especially on Japanese automakers. Two turbos operating in sequence theoretically offer the quick spool of a small single turbo, with enough oomph to deliver lots of air, and thus, horsepower, boost at higher engine speeds. Twin turbochargers operating in series-where one feeds the next-have the same problem. A large turbo may provide the desired peak power, but it takes a long time to spin up a big turbo, leading to big-turbo lag. The principle behind a sequential turbocharging system is fairly basic. Yet, the next time Porsche offered a twin-turbo car, the 993-generation 911 Turbo, the 959's sequential system was abandoned. All of us spoke in hushed tones about what happened when that second turbo was going. A couple colleagues also drove the 959 that day. Below 5000 rpm, it feels like a pretty quick old 911 above, it's astounding, with an almost violent surge to its 6500-rpm power peak. Out around Sonoma, the 959 felt like nothing else. If the driver went to wide-open-throttle at 2500 RPM, the 959 would reach its maximum 14.2 psi of boost in two seconds, whereas with a simple parallel twin-turbo setup, the same would take 6.5 seconds. Paul Frere's The Porsche 911 Storyhas a fabulous explanation of the 959's complicated plumbing system, but all we really need to know here is that the system reduced turbo lag significantly.
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