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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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