General turbo question...

[Aahz]

Iv argued this question on both sides but have never gotten a definitive answer from anyone. Will a turbo spool up and give you any kind of usable power when you rev the engine at a stand still? At first I thought not because of needing air movement in the intake to spool the turbo but then somebody pointed out that it's actually exhaust vacuum that causes the turbo to spool so the engine revvin might cause it to spool. SO which is it?? Or are both theories bunk?
Thanx to any who reply

 

[reckedracing]

revving the motor should spool the turbo except for 2 problems...

1. cars equipped with turbo controls that keeps the wastegate open until its gotten moving...

2. as soon as you let off the throttle its going to sense extra boost and open the wastegate...

 

[dohcvtec_accord]

Exhaust "vacuum" doesn't cause a turbo to spool. Spent exhaust gasses do, though.

On most factory turbo cars, as recked pointed out, there are usually measures built in to keep the wastegate partially open so the turbo won't reach FULL spool. However, on Subies (for example), they'll reach about 2-3 psi so that there can be some power had off the line. I imagine that, on a custom turbo setup (or custom tuning on a factory turbo setup), you could keep the wastegate shut at a stop. Most transmissions, however, wouldn't like being subjected to full boost immediately after the clutch is released, however.

 

[posol]

on a MAF equipped car, it is possible to create boost without engine load. a small turbo may even reach full boost.

on a MAP equipped car, it is not, without doing a bunch of blip-revs to mimic engine load, and having a dinky ass turbo. and even then, it is rare to see more than a couple of pounds...

if you set up some sort of ignition retard to have post ignition on a 3=-step, you can actualyl use the "backfire" to spool the turbo... the combusting will happen in your manifold and cause a lot of energy to be released and create flow over the turbo.