[aws]

Derek: You need at least a 1 5/8 exhaust diameter in order not to give up any horse-power. Recently I used a set of 1 1/2 diameter SSI's on a fairly aggressive 3.0 for the street (10.5/1 twin plug, modified GE-80 cams, 3.2 ported heads, 42mm vent in 46 IDA's) and it just seem to increase the low end with a small decrease in total power. I don't have any dyno numbers to confirm this beyond seat of the pants---It is one of my race engines I refreshed and stuck in my street car.
aws