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Yet another way to look at it. Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 16 Jan 2003 13:04:45
In Reply to: Is my turbo functioning properly or not? Confused (long, Tony O, Thu, 16 Jan 2003 05:11:19 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Perfectly normal. Remember how things are connected - air comes in the air filter, gets pressurized by the turbo, then goes THROUGH the throttle plate to the intake manifold to the engine. (Yes, there is an intercooler and other stuff, but ignore that for now).
The turbo gauge is measuring the pressure in the intake manifold. That is on the engine side of the throttle plate.
An engine is just an air pump. When the piston goes down on the intake stroke, it sucks in air from the intake manifold. When it exhausts, it exhausts it out the, well, exhaust. The engine pumps air, uses fuel to help it pump air. Clever designers use the rotational energy left over to drive the wheels.
All the turbo does is cram air into the engine. More air, more fuel, more power.
When you go to shift, not only do you push the clutch down, but you also back off on the throttle. The throttle plate closes, but the engine is still running at high RPM. So the 'pump' of the engine sucks the intake manifold of its air - a vacuum. The turbo is still running - it's pressurizing the system, but on the OTHER side of the throttle plate. So yes, the gauge will drop, as it sees intake pressure, not turbo pressure. Perfectly normal.
In fact, the turbo is frantically trying to stuff air into the intake, but instead is hitting a closed throttle plate. This can cause a very high pressure to buildup in the intake system (on the turbo side of the throttle). This produces a pressure wave that flows back and 'stalls' the turbo. To prevent this, there is the famous "hooter valve", technically known as the Turbo Bypass Valve. When the throttle closes, this valve opens up and ports high pressure air from the turbo side of the intake back to the input of the turbo. This allows the turbo to keep spinning at high speed, so it's there when you complete the shift.
posted by 192.249....
, Thu, 16 Jan 2003 13:04:45 <-- Viewing This Message, Thu, 16 Jan 2003 12:18:00, Thu, 16 Jan 2003 16:36:18
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