precompressor density increase > intake mani density increase
EDIT: Technically the above is wrong, but was written in the sense that making increases in precompressor density is more worthwhile than post compressor increases, although you can more easily increase density post compressor due to the larger deltaT of the now compressed air.
A better way to put the above is: post compressor density increase = PR
* precompressor increase for the same mod. /EDIT
This is especially true with smaller compressors, or will make a bigger difference to you. With a larger, efficient compressor you just turn up the boost...but in trying to eek every last little bit out of my tiny IHI I did everything I could to get the densest, coolest, highest pressure air into the compressor intake.
A given pressure ratio does not equate to an absolute mass flow rate. A 2.0 pressure ratio simply pressurizes the air to twice what it was at the intake. It does not care what the intake pressure or density was, it will operate as efficiently as it's flow map dictates at that pressure. What does change is the air mass. You can effectively "shift" your efficiency map by providing denser, or higher pressure air. This is how compound turbocharging works, and why the second compressor on such setups doesn't need a huge pressure ratio, just a high flow rate that is efficient for said pressure ratio.
The RHB5 was only efficient up to about 1.7 pressure ratio for the 1.6L, and blowing nothing but hot air after that. Coupled with a tiny intercooler on the original BEGi kit and I had to do what I could to direct cool, high pressure air to the intake.
Either way you're optimizing your setup. It amazes me that we can spend $200 for 5hp, but will scoff at the $6 solution that nets just as much gain, especially when it's one that makes life easier on both turbo and motor.