MANDALAY
My IAT's are low being a SC which is great one of the things over a Turbo but i want to get it as close to ambient as possible and to improve recovery
You've mentioned your low intake temps a few times as compared to turbos, implying that the Rotrex heats the air less. In fact the opposite is true, and I'd suspect your low intake temps are testament to the effectiveness of your intercooling system.
It is a known physical property of gases that an increase of pressure results in an increase of temperature in the absence of any other energy transfer. This is known as an adiabatic process and can be approximated with the ideal gas laws. It doesn't matter how the pressure is raised, if no further heat energy is added the final temperature is the same.
The other significant factor affecting the final gas temperature is the compressor efficiency. Centrifugal compressors by their nature have a rotational speed range where their efficiency peaks, and the highest absolute peak efficiency is achieved in designs where this speed range is narrow. The Rotrex compressor must provide usable efficiency over a wide range of compressor speeds, dictating that its efficiency island is wide but not terribly high. Therefore its peak efficiency cannot by its nature match a turbo which can be optimised for the narrow speed range that the wastegate regulates it to. It should be noted that a centrifugal compressor's pressure ratio is loosely proportional to its shaft speed, regardless of actual flow rate. For example, on a given engine/turbo configuration, the turbo might be doing 90K RPM at 12 PSI boost and 3000 engine RPM, but at 6500 engine RPM with double the air flow but the same 12PSI, the turbo would only have raised to maybe 105K RPM.
So the net temperature rise through the compressor is defined as the product of compressor efficiency and adiabatic thermal effect. The former is lower in a turbo due to its higher peak efficiency and its ability to operate within that narrow efficiency range, the latter is an unchangeable physical property identical between the Rotrex and turbo. It therefore makes sense that the Rotrex producing the same boost as an equally well matched turbo will have a higher compressor outlet temperature.