Head work will get you 400RWHP using the stock 930 manifold with stock 7.0:1 compression at 1.0bar or less. If you bump the compression to 8.0 you can get your 400RWHP with less boost and a little better response.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8