Having read many comments on engine operation by R.F., I'm confident that running an LS3 at 3600-3900 rpm is not going to hurt it one bit. The redline is north of 6200 rpm. So cruising at 3800 rpm would only be about 60% of the engines operating range. Robinson said to run it at 4000 rpm in cruise. And that may be where the 18 gph is. I am a believer in running engines as they were designed to be run. But I will not shove the throttle wide open, rather, a slow continuous push to the desired power setting will be employed. This is inflight, and on the ground for takeoff. The big 94" prop has a big arm moment. Just got off the phone with the folks at Supermarine Spitfire. They have been running LS2's / LS3's in their Spits. At high cruise, 3600 rpm, they claim a fuel flow of 14 gph. And a corresponding airspeed of 193 knots.