![]() Some designs combine the intake charge from each turbocharger into a single intake manifold, while others use a separate intake manifold for each turbocharger. The reason for this is the location of the exhaust manifolds on cars with two cylinder banks make a single turbo impractical to route.Porsche 935 flat-six engine with parallel twin-turbosĪ parallel configuration refers to using two equally-sized turbochargers which each receive half of the exhaust gases. Most cars on sale today with twin-turbos are parallel V or flat-engined cars, like the Porsche 911 Carrera. It’s just two turbos working to make more airflow. Most modern twin-turbo cars are much, much simpler parallel twin-turbo cars. Mazda used a nutty vacuum system to carefully measure engine load to determine switchover conditions, with a strange-looking siamese exhaust flange and turbos. The methods to achieve the switchover vary greatly, with Toyota using physical flaps to force more air into the primary (small) turbo, and opening the flaps above 4,000 RPM for the secondary (big) turbo. The A80 Toyota Supra used a sequential setup as well, with a smoother switchover. The FD Mazda RX-7 used a sequential turbo setup that switches around at 5,000 RPM, making for two very distinct powerbands. It may seem a little hairbrained, but sequential twin-turbos in fact work that way. The most important distinction is that sequential twin-turbos share the same exhaust gases, and they pass through both turbos on their way to making boost. That basically means that they feed pressurized air to the same pipes. These turbos also ingest air separately, and do not feed each other, but they share a charge air system. Like discussed earlier, a smaller turbo works better at lower RPM, and a larger turbo works better at higher RPM. Sequential twin-turbo means that there are two slightly different turbochargers working together to achieve a very wide power band to make the engine responsive and usable at low speed, but have the high-speed kick of a larger turbo. ![]() Completely confusing, right? – Image: Wikimedia Commons An excellent diagram showing how sequential twins work on a 2JZ A80 Supra, specifically the “pre-spooling” stage where the 2nd turbo is getting fired up. The turbos ingest air separately, and do not feed each other, and they also receive separate exhaust gases, which is what makes them truly parallel twin-turbos.Īn old Supra site actually has a great writeup of various twin-turbo setups that can be used with the venerable Toyota 2JZ, and though the resolution on its illustrations are a little dated the information is timeless and nicely organized. Parallel twin-turbo means that there are two identical turbochargers feeding air and functioning as one, to achieve more power and efficiency than a single larger turbocharger. It gets interesting when we start talking about parallel twin-turbos or sequential twin-turbos. A less confusing diagram about good ‘ol parallel twin-turbos. Bi-turbo and twin-turbo is just nomenclature, no functional differences exist between the two. There are two turbos hanging off of your exhaust manifold. ![]() Enter twin-turbochargers.īi-turbo, twin-turbo, parallel twin-turbo, or sequential twin-turbo they all mean the same thing. Back in the day, before every manufacturer on Earth made a mass-produced turbo engine, the technology was young and inefficient, requiring big band-aids to make work in performance applications. The more air you can catch and release, in the least turbulent (or sometimes most beneficially turbulent) way, is the big secret of turbo efficiency. An oversized turbo will make the car sluggish at the bottom, raise the boost threshold, and potentially be laggy, even if it makes excellent high-RPM power. An undersized turbo for an engine will make it efficient and punchy in low to mid-rpm. Another fun thing to consider is turbo size affects your power band. ![]()
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