| If you have a look at the Garret graph. Notice that the lower scale is actally in Lbs per minute of air. We are talking in PSI. PSI is not an absolute pressure measurement. We normally talk PSI but neglect to note the temperature that the charge is at to get the PSI we talk about. 28 PSI at 800 degrees have less volume in lbs per minute than 28 PSI at 500 degrees. So if you look at an engine with significant restriction. The temperature of the charge after combustion is significantly higher than a low restriction engine. This means that the actual lbs/min rate lower for the higher temperature engine moving the graph lower down into the graph. So what Greg is saying is that by removing the restrictions in the engine and letting it flow better. We have now changed the PSI scale that I added on the graph I did so that it no longer relates to the lbs/min scale as it did before. Reducing the engine back pressure has now caused the turbo to fall off the high end of the scale and essentially is now seems smaller than we thought it was. This not neccesarily a bad thing as we can now hit max boost for that turbio and hence maximum power at lower boost levels. The turbo has a maximum boost point that has now been reached. (max efficency) Having said
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