Maul driver....the reason speed does not vary much with RPM when LOP is that HP is a function fuel flow, but when ROP it is a function of Mass Airflow. Have a good look at the APS/John Deakin graphs and you will see why
I am with Scott, we have 600 hours and we are LOP all the time and I say 160+/-4 depending on level, temps, turbulence, and up in the FL's we find that we are usually around 157TAS on 35LPH compared to 40-41 down lower.
Now, as for your questions about your speed........which is really why you asked in the first place.
1. Have you installed all the fairings and wheel spats? If not...You should.
2.Have you done a 4 way GPS box test and compared this to your indicated TAS on your EFIS or one calculated from IAS etc. If not you need to do this.
3. Which kind of static port have you used?
The reason you need to know these things, and the reason I ask is that if you dig back through the records, I was baffled why we had the slowest RV10 in the world. I soon discovered we did not, it was like all the others, fast!
So it was all about static vents, I started experimenting by glueing a big rivet head like the Vans one over the static port disc, now I had the fastest RV10 in the world
, but of course that was wrong.
This is my experimental static port below, and once I jagged it right....well It works so don't muck with it!!
By the way some on RV7's have been the same, a small fence in front of the port corrected big errors there too.
Now as you can imagine, this static error has a corresponding effect on your altimeter and encoder, so your Transponder is reporting false altitudes and your alimeter is too. I did some calculations based on 160 knots and whatever else I needed at the time and the error was around 140 feet. And Speed effects it, less error the slower you go.