hi - i just bought my 05 WRX and it also happens to be my first turbo charged car. I LOVE IT!! but i do have a question on the boost gauge. the vehicle had a SPT boost guage in it when i bought it and it seems to read in the negative alot during normal driving, when i am not really getting on the gas. now i was under the impression that it should be staying in the positive unless i am between shifts or engine braking/off the gas completely? is this normal? and if so isn't that also causing my turbo to spool down?
Negative numbers (vacuum) are absolutely fine during normal driving/cruising...when you accelerate anywhere from a little to WOT, then you should be hitting target boost levels (ie. in the positives on the gauge).
Also, I'm not sure what you mean by your turbo 'spooling down' but the gauge and its readings don't have an impact on your turbo's spooling properties.
When its in the vacuum side of the gauge the turbo is spinning faster than the exhaust gases can push it creating a vacuum, this is what you might be referring to as "spooling down" but its perfectly normal, When you floor it the exhaust gases are moving faster than the turbine causing boost. For every action there is an equal and opposite reaction, some gauges dont even have a vacuum reading on it.
ok so if am undertsanding correctly then when i am in the negative, or creating vacuum, that would consequently be slowing down my turbo impeller? which i don't want. and does anyone make an exhaust gas bypass to prevent this???
its not 'slow' perse. its spinning backwards. there is a load on the impeller its just reverse. the exhaust gases will leave the system at a normal rate, the impeller should not hinder the flow.
i think your worried about a lack of performance under vachume. but its a nil point. 1) if your in vac your not big on the throttle and must not be accelerating very quickly. 2) when the impeller is under a vac load like that it wont take much at all to get into the posotive. if your pulling a crap load of vac then your probably in the sweet spot rev wise and just need to use teh go juice.
To sum it up for you, its normal dont worrie about it. It doesn't hurt anything, you are going to get the best gas mileage when you are in vac.
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