Your prolly right about the exhaust.
But, thats the point of the exercise and most of the fun. We park a big airflow device on there and systematically remove bottlenecks until we get the ponies were looking for. Then we get to quantify the gains at each step.

Im running a .87 in the PE from 3500 on up. It's pulling about 9% fuel under boost so it may be a touch rich, But within the range of the WB.
I get no knock with the stock timing tables, havent looked for power in them yet.