n20fed

I've got a 355"95 z with ported afr's,big hydraulic cam, th400,3800 verter,etc,etc.
I went to the dyno yesterday and put close to 400hp to the wheels naturally aspirated. I then added some 100 unleaded fuel. I have a nx dp kit jetted for a 200 shot. The car Na peaks at 6600. I have a dedicated pump for the nitrous. Basically I couldn't get the a/f richer than a 13.5. I had also pulled out 8 degrees of timing from my msd timing control, but the knock sensors still pulled another 4 out. NA timing is at 37 degrees. I believe that the piston in the fuel solenoid is bad, because I had my holley blue flowing almost max at 13 psi, and I started out 9 psi. After increasing pressure 4psi, it only changed my a/f by 1/2 point. It picked up a litle over a hundred horse at 5600 and was pulling 4 degrees of timing out. I've got a new piston on the way for the fuel solenoid. Any idea on how much hp can be gained by richening the a/f down to a 11.5? At 5600 NA the car put 349hp down with a a/f of 13.25.