What RPM engages the turbo?

[Volta]

Hi all,

Well, it's been exactly one week and a day since I purchased my '94 850. I really enjoy the car so far. I'm just crossing my fingers nothing goes wrong.

One question, however. My turbo gage shows the turbo engaging at 2,000 RPM. Is that normal? I thought most Turbos engage at 3,000?

Also, while the car idles, the turbo gage isn't resting to the extreme left (or, what i would consider the furthest point from engaging). Instead, at idle, the turbo gage rests between the furthest point from engaging, and the white bar that indicates the turbo's been engaged.

I have no idea if this is even a problem. I'm pretty inexperienced when it comes to the mechanics of a car, but I do plan on learning this one.

Thoughts?

[Jaxx]

the beginning of the white bar means that it is about to spool...

in the white is spooled up.

also depends on how hard you're gassing it, dont worry if the gauge is off, the stock gauge isn't exactly meant to be used as a exact measure.

hope this helps,
-jaxx

[adamc]

The turbo is running ALL the time - it simply boosts the air pressure before the butterfly valve (in front of inlet manifold). The faster the engine is working, the more the turbine (turbo) rotates, providing more air (pressure) to the inlet manifold. The turbi guage shows both vacuum and pressude with atmospheric pressure being in the centre (check when motor turned off). At idle, engine is starving (ie vacuum) but when you put your foot down, you open the butterfly valve allowing more air to enter the engine. A normal car goes up to atmospheric pressure as its maximum, but with a turbo, that air pressure is boosted by as much as 1 atmosphere positive (actually around 13 psi). By boosting the air pressure, the engine is able to take a bigger gulp of fuel-air mixture hence a bigger bang and more power (almost doubles - so that makes a 2.4ltr engine give out the power equivalent of about 4 ltrs). When the turbo guage is in the positive (past the mid-point) it means your manifold air pressure is greater than the outside (atmospheric) pressure - hence you are boosting the engine's power. The further the guage shows positive, the more you are ramming air into the cylinders. When it is negative (les than midway) the engine is acting like a normal (non-turbo) engine. The negative air-pressure shows that it is being throttled back (normal crusing or idle mode). Hope this helps

[Guest]

The turbo is running ALL the time - it simply boosts the air pressure before the butterfly valve (in front of inlet manifold). The faster the engine is working, the more the turbine (turbo) rotates, providing more air (pressure) to the inlet manifold. The turbi guage shows both vacuum and pressude with atmospheric pressure being in the centre (check when motor turned off). At idle, engine is starving (ie vacuum) but when you put your foot down, you open the butterfly valve allowing more air to enter the engine. A normal car goes up to atmospheric pressure as its maximum, but with a turbo, that air pressure is boosted by as much as 1 atmosphere positive (actually around 13 psi). By boosting the air pressure, the engine is able to take a bigger gulp of fuel-air mixture hence a bigger bang and more power (almost doubles - so that makes a 2.4ltr engine give out the power equivalent of about 4 ltrs). When the turbo guage is in the positive (past the mid-point) it means your manifold air pressure is greater than the outside (atmospheric) pressure - hence you are boosting the engine's power. The further the guage shows positive, the more you are ramming air into the cylinders. When it is negative (les than midway) the engine is acting like a normal (non-turbo) engine. The negative air-pressure shows that it is being throttled back (normal crusing or idle mode). Hope this helps

Wow. Yeah, that helps. I don't understand 90% of what you said, but I get the gist. I'm not worried about it anymore.

Thanks again. You guys are great!