your statement is way too broad - not all small blocks are created equally - nor are all big blocks... MOST mid-level performance engines will do well with a 2.5" system - big or small block.. but once you get into the higher HP ranges (I think someone aptly stated above 450HP) a 2.5" system could be restrictive - again, big or small block. I would venture a step further - if you are approaching 400HP - a 3" system will likely work well for you.