boost and bar ???

In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm)
 
Bar or psi is used to tell you the air pressure that the turbo has created by pumping air into the inlet manifold... Like your car tyre has say 30psi of air pressure in it, on full boost your car will have x amount of air pressure in it
 
[quote author=willyob link=topic=42621.msg488138#msg488138 date=1409506281]
iv heard people saying they boost at 1 bar or 1.5. is a higher bar (psi) not better to boost?
[/quote]

Depends on engine components, intended use, ECU map etc.
One boost value can be great in one scenario and terrible in another scenario.

As a very basic rule of thumb: factory Subaru boost levels are max about 0.9-1.0 bar, a typical "mapped" car would see values of 1.0-1.3 bar.
Values higher than 1.3 bar are seen, but would usually mean it is an engine with a lot of work done like forged internals, uprated studs and much more, as the risk of damage on stock parts is too big at high boost pressures.

BTW 1bar is the average absolute air pressure at sea level. So when you see 1bar boost, it really means 1 bar over relative air pressure, or with other words the pressure in the inlet manifold is approximately 2x the normal air pressure outside.
 
[quote author=willyob link=topic=42621.msg488145#msg488145 date=1409508070]
is it better to boost at 1 bar or 2 and can you change when you boost? :imnewhere:
[/quote]

Either using the ECU map (read settings), or using a manual boost controller allows you to control the level of boost pressure.
Your potential highest boost pressure depends on your engine, the turbo used and the RPM (a car will make more boost at 4000rpm than 1000rpm for example). The engine components, turbo, exhaust work together to give a potential boost profile (when boost will first build, when you can hit full boost, how long it takes to rebuild boost after you come off the throttle etc). Some cars can boost 1bar by 2600rpm and others can only hit 1bar by 3500rpm, regardless of any ECU or boost control settings.

Whether 1 or 2 bar is better is not a question that can be answered here with the level of info available, though for most the right level will be much closer to 1 bar than 2 bar (see my previous answer).

Is there something specific you are trying to accomplish?
 
:goodjob: I think im with you. so what if I rev engine to high wihle driving or stopped will the guage go up to 2 bar and blow up the engine?
 
[quote author=willyob link=topic=42621.msg488153#msg488153 date=1409509000]
:goodjob: I think im with you. so what if I rev engine to high wihle driving or stopped will the guage go up to 2 bar and blow up the engine?
[/quote]

It shouldn't... unless something is configured for it to do this.
 
Only adjust the boost when you get it mapped, the mapper will configure the boost, otherwise the fuelling will be off by quite a way if you do it manually
 
I was just worried if I drive it 'wrong' (too high revs or anything like that) and I hit 2 bar will it blow up (newbie to turbos sry)
 
No, the turbos will run out of puff and the boost will drop as you go up the revs. No point taking a B4 past 6,500 revs as there is no power. Just remember they are not Hondas that you rev the balls out of and you'll be grand.
 
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