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Re: That really depends where you mark your ambient place
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Posted by aero guy (more from aero guy) on Thu, 2 Aug 2001 20:51:54 Share Post by Email
In Reply to: Re: Turn off the engine, the gage should be on the line between, markw, Thu, 2 Aug 2001 15:25:59
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as soon as you open the throttle butterfly the engine intake valves see pressure of the ambient rather than vacuum. this increases the volumetric efficiency of the engine and thus more exhaust flow this spins up the compressor and more air is pumped to the valves and the process starts all over. Boost (1.001 bar) can begin at as low as 1150 - 1200 rpm IF the throttle valve is full open and the engine is loaded heavily. The TD04 compressor will actually start producing boost slightly above idle (1000 rpm) under the right conditions. Your car has the T25 compressor and it will start at about the 1150-1200 rpm.
If you are asking if you are getting boost above ambient if the needle is above the point of gage with engine off and that is what you call neutral, then the answer is yes. You are so far down on the torque curve that this boost is in essence useless. You are increasing horse power with the boost, but it is the torque output that makes the car go. Usable torque really starts peaking around 1800-1900 rpm on the 2.3 engines This coincides closely with turbo boost rate increase and you can actually feel a double surge of power around 1900-2000 rpm the first is when the cams come in and the second when the turbo reaches maximum volumetric effeciency. Taking into account Turbo lag, this is around 2800 rpm. This is not max boost, but max delta P across the gas turbine blades around 75-85000 rpm. Maximum boost is around 110,000- 120,000 rpm depending on the compressor unit. Early books show RPMs of around 127,000 RPMs for max boost but most of those data are for very early turbos. Hope this answers your question.
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