I lay down for about 8 hours and the master himself asks me a question! :doh: :rolleyes:
First thing first - at max impeller RPM we have max airflow into the turbo. This the only thing you can really -hear- because it's loud, and the interaction between the intake manifold / valves and the impeller isn't really heard for the purpose of what we're discussing. The impeller taking in air is what we hear, rather than the engine taking in air (semantics, but still). At X impeller RPM, the turbine will move X amount of air (basically, save for losses due to pressure buildup etc). The sound created by the impeller will get louder with impeller RPM, but also with pressure buildup since air on the output side is generating friction by providing backpressure on the impeller. This is why the sound should be related to impeller RPM, but
also as pressure builds up there should be a further increase in volume. This is what I was saying in an earlier post, that the increase in volume is not linear to impeller speed and this is why...
Turbines are only efficient at specific RPMs, which is one of the problems in LFS. LFS doesn't appear to model the efficiency range of the turbocharger's impeller as it is, and I think this is the big reason for the "bigass lag" problem (although the GTRs cars are probably not that far off TBH, huge turbo, tiny efficiency range). It will tend to spool very easily (not linearly like in LFS) up until it hits it's efficiency range, so most of the spooling should happen much faster - this is missing in LFS. Really, would should happen is that the cars should start to loose boost at higher RPMS, which they do not. In the LFS world, the turbo can supply enough air no matter how high you rev (WAY past the engine's torque peak) and this is a short comming. The only alternative to make it work, is to make them act like the RAC which is dead wrong - the impeller RPM and boost pressure are always too related (higher boost at lower RPM needs less impeller RPM, but very little is generated...).
This kind of went way off track, sorry :sadbanana
However, when you do decide to look at boost modelling please have a look (if you haven't already) at how compressor maps work
http://www.rangerpowersports.com/tech/?p=132 and this should clear things up a lot... I'm sure you know most of it anyway, just trying to help
So, if at full throttle in the XRR, max impeller RPM occurs around 4500, along with max boost, then our wastegate will kick in and allow exhaust out of the turbocharger's turbine housing to stop boost creeping, since we want it maxed at X lbs (24?). Thus, the turbocharger is pumping it's max volume of air into a particular demand for the engine (XXX CFM) At 6500RPM, the turbo is still working as hard as possible, max pumping, but the engine now demands more than XXX CFM to maintain 24LBS, thus some pressure should've been lost. (small turbo efficiency range - probably totally right for a GTR car). Road cars behave similar, but generally the turbos have better (more suitable) efficiency ranges to make them driveable, plus they're not usually trying to maintain 2 bar
. So, yes it's a problem with the model - but the fact still remains - the air sound must inherantly be related only to the amount of air the turbocharger is pumping, and also be affected further by how much pressure already exists in the manifold.
Hope this makes sense, sorry for my tardiness - living across the world has disadvantages