Turbo pressure withuout gear engaged

**alfista_AR** · 27-02-12, 18:31

Hello there,

Need some help regarding turbo pressure

Wich should be the pressure when no gear engaged and motor revs. at 3500/4000 ?

I can see only vacum (-0.5 bar) on idle,an this is normal, but no positive pressure at all even when reach 3500 or 4000 revs.

I suspect that it's losing air at some point.

Thanks.
-DO.

**mpampis_** · 27-02-12, 18:52

It is natural. Without gear (neutral) the only way to see boost is with WOT and no more that 0.4-0.5 bar. If you had a leak I think you would have unstable idle

**Steve Webb** · 27-02-12, 20:16

Because spinning the engine up with no load doesn't take much power, you won't see any real boost, certainly not if you are holding the engine at a set rpm.
The Turbo relies on exhaust gas pressure to create boost, so if there is no real load on the engine, you won't be passing much fuel through the injectors, which means not much in the way of exhaust gas, so nothing to spin the turbo with.

You can however see some boost if you blip the throttle several times, it won't be much though.

**AlfaJack** · 27-02-12, 23:22

It is the same as driving at a steady 4000rpm on the motorway, it won't give any boost. But, when you put your foot down, you are still at 4000rpm for a short while but with 1 bar boost as it is filling the bores with petrol and creating much more gas pressure.
(It has taken me 7 years of Q4 ownership for my little mind to work that out!)