Originally Posted by
Payu E cover its .60 A/R will help for spool and response will sacrifice some top end...
S cover its .70 A/R comes plain, bullet hole or machined anti surge more lag but more top end... Most result you will get over the net are with the bullet hole S cover....
This is wrong, compressor housing size does not affect spool.
It also makes a minimal impact on HP since they typically change the radius and keep the area roughly the same. The reason for running different size A/R's is because with a smaller A/R, the efficiency is increased at higher boost levels due to less compressor power needed to fill the area of the compressed air exiting the housing.
A larger A/R helps the surge region of a compressor for lower boost applications, which is why the larger A/R housings typically have the anti-surge housings.