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Location:
NSW.south coast.Drifting
Registered:
February 2004
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 Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 04:26
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can anyone please tell me how these 'sequential' turbo systems work? im in first year at uni doing mechanical engineering and any info would be of great help. (i just need a basic outline of how these systems work)
thanks
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Location:
Cabramatta, NSW
Registered:
May 2002
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Re: Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 04:36
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The system that Mazda uses in the FD RX-7 uses two turbos of different sizes.
The small turbo spools up first 'coz it's small and masks the lag of the larger turbo. The larger turbo takes over in the top end where the small turbo runs out of puff.
Not sure if there's a switch over or if both turbos are always run.
The sequential system of the 2JZ-GTE found in the Supra has two turbos of the same size. One is on constantly, the other is brought on at about 4,000rpm where it provides more breathing.
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Location:
Brisbane
Registered:
May 2002
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Re: Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 05:18
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Nark is correct. The 2JZ-GTE uses a system of computer-controlled valves to make the sequential system work.
At low rpm the exhaust path out of the second turbo is blocked by a butterfly valve, and all exhaust gases are redirected to the first turbo by a crossover pipe. There is also a valve just after the compressor outlet of the second turbo which isolates it from the inlet system and prevents back-flow.
At a designated point based on rpm and engine load, the ECU opens up the exhaust valve which allows exhaust gases to flow through the turbine of the second turbo. After the turbo has spooled up to match the first turbo (I'm not sure how this is determined by the ECU), the valve in the inlet side opens up and the engine is in twin-turbo mode.
The result of all this is an amazingly tractable engine which can develop positive manifold pressure at nearly any engine speed, while still having a screaming top end. Unfortauntely the system isn't perfect though; as soon as you increase the boost pressure or even install a free-flowing exhaust, things don't work as smoothly as they should. In my case there's a noticeable trough in the power curve as the engine changes from single to twin turbo mode, which can be a little off-putting or even scary in some situations. That's why I disabled the sequential system in my car and have it in twin-turbo mode all the time.
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Location:
NSW.south coast.Drifting
Registered:
February 2004
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Re: Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 08:53
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ok so small turbo runs first into the intake, to 'mask' the lag from the bigger turbo and then when the engine has enough rmp, the larger turbo gains boost? in other words the exhaust gasses flow through BOTH turbos, just one spools up quicker.
thanks for the help guys
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Location:
Cabramatta, NSW
Registered:
May 2002
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Re: Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 09:19
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That's for the Mazda system.
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Location:
Brisbane
Registered:
May 2002
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Re: Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 23:45
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Subaru also has a sequential twin turbo system on one of the upper-spec Liberty/Legacy models, but from what I've heard it's ludicrously complex and somewhat unreliable.
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Location:
Cabramatta, NSW
Registered:
May 2002
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Re: Toyota lexus and mazda turbo systems
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Tue, 16 March 2004 23:51
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Yeah, the B4. I've heard bad things about that system too.
Doesn't seem to work too well.
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Location:
near chris and murray vic
Registered:
July 2002
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Re: Toyota lexus and mazda turbo systems
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Thu, 18 March 2004 03:34
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afaik, the mazda has a switch from one turbo to the other
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