Turbo PSI/Efficiency vs Engine Capacity

[rorge]

So this has come up in my headgasket thread and I think it's threadworthy..

I'm fairly sure i've learnt in the past that a 1.6ltr engine flows a different amount of air to a 2.0ltr engine..

Here's the possible grey area of my learnings...

When a turbo is providing a given PSI to a lower capacity engine it is actually working more efficiently (well moreso not as hard) to provide that same boost due to the reduced capacity the engine can flow....???

Is this right?
Discuss and make me learned!!

[Billzilla]

I'd guess it depends where the turbo is on the compressor map, so not really enough information.

[Coffin]

I thinks its more like, if an xyz turbo was out of its efficiency zone @ 20psi on a 2 ltr, would it still be out of its efficiency zone @ 20psi on the 1.6ltr

My uninformed conclusion is yes, as the compressor map is the same, 20psi is still the same 20psi on the compressor map

[Scuba-Steve]

Two factors, a compressors efficiency island is defined by flow and pressure ratio.

Flow is the volume of air
Pressure ratio is the boost pressure

Here is a compressor map


Pressure is on the vertical axis Flow is on the horizontal axis.

Your theory was if it flows 15psi on a 2litre then 20psi on a 1.6 is about the same. Well this may be the case on the airflow volume but take that airflow figure and move it up to the pressure ratio you want to run and see if its still in an efficient area of the map.

That said in your case its probably wont be too bad.

[GreyBeard]

it's all about mass flow & p/r, not volume & psi
forget psi and volume, learn to read a compressor map
and don't forget the turbine map is equally important.
the rest is just bullshit for boostloosers to get a high post count

[9triton]

put some numbers here: and play around - can compare maps:

http://www.squirrelpf.com/turbocalc/

[CussCuss]

is a pressure ratio of 2 1 bar (as we measure it)? ignoring things like compound turbos and shit, but in normal application?

[Shifty]

2bar = 1 bar boost

and yes you need to look at flow vs boost as this is the point of relevance for engine capacity changes with the same turbo