Interpreting the Boost Gauge

[chrispazzi]

I don't know much about turbos yet and would like to know a thing or two about what it means when my boost gause shows different pressures.

 

Any light anyone can throw on what my turbos are actually doing when the gauge is reading different figures (explained below) would be appreciated.

 

The boost is always in one of four readings when I'm driving. Here's the readings and what I think they mean (I could be totally wrong though!).

 

1. -0.5bar at idle and low revs/load

Are both the trubos idle? Does this mean that the turbos are therefore not spinning and are cooling down even if the engine's not at idle (e.g. trundling down the street at 15mph)?

 

2. 0 bar at light load and low/medium revs

Turbo 1 spooled up but not boosting?

 

3. +0.4 bar at meduim+ load at 2-4k revs

Turbo 1 is boosting?

 

4. +.8 bar at medium+ load and over 4k ish

Turbo 2 (and 1) boosting?

 

The only other thing I know (or think I know) is that if the gauge flies off the scale to stop the engine before the turbine blades fly clean through the bonnet!

 

[Alex]

1. ) Is a vacuum - this is negative pressure (less than atmospheric)

 

2.) This is atmospheric pressure.....IE no boost or vacuum

 

3.) Turbo 1 only

 

4.) Turbo 1+2 runs a higher boost than 1 on its own.

 

 

1.) Should be even lower when you let off the throttle after boosting....nearer .7

 

What's the scale of your boost gauge what does it read up to??? On standard turbo's you don't want to go above 1.2-1.3 bar.

If you lift off the throttle your boost can't fly up!!! What on earth kinda failure would cause that anyway!! Never ever shut your engine off in that way....you shouldn't even shut it off straight away after finishing a journey.

 

Unless you've literally blown the engine up there is no excuse for turning it off in that manner.

[chrispazzi]

The gauge goes up to 1.5 or so. I've not noticed what it does at gear-changes or lift-off, I'll have a look next time I'm out.

 

Thanks for the note about not swithcing the engine off too hastily, that would be a costly mistake!

 

[Adam W]

The turbo uses energy from the exhaust gas stream to spin round, kinda like a water wheel in a river. The faster the river is flowing, the faster the wheel turns!

 

What this means is, the more exhaust gases are being produced by the engine, the faster the turbos spin, and the more boost is produced. Peak boost will be when you're foot to the floor at 4500+rpm. At low throttle or very low revs, the turbos are barely spinning at all, just like when the engine is idling (as you say).

 

There is no reason for your boost to suddenly go very high, so don't worry about that, but should you ever get concerned about the boost level simply lift right off the accelerator and your boost will drop instantly.

 

The ECU has a built in safety cut out which will activate before the boost level can get dangerously high, so don't feel obliged to watch it like a hawk.

[Need4Speed]

At least you have a boost gauge and are paying attention to what it's telling you.

[Terminator]

Chris, from the readings you are quoting, it sounds like you are running stock boost, just what your turbos are designed for so no problems. While it is possible for blades to be damaged, that is more likely to be caused by foreign bodies impacting with the turbines, usually down to poor filtration.

 

There are guys on here that have seen 1.4 bar and higher, me included, on stock turbos and they are still fine. BTW that level of boost is not recommended. Running stock boost and stock turbos one car has passed 300,000 miles and still going strong. Just do regular oil changes with a good oil and follow hand book cool down periods before switch off and you will be fine.