2.5'' on 318?
I've ran a 2.5" system on my dart with a mild 318 with headers the car ran fine,with no problems at all,sorry I cant give any e.t. as ive never raced the car,but it was alot of fun on the street.I'm restoring it and putting the 340 back in,with stock manifolds.The headers seem to bottom out on right side.Headman headers is what I ran,oh well, live and learn. Good luck!