After Doug said that this thread was appropriate, he re-opened it. Thanks Doug!
Let the informative dialog begin anew on LS-3 cam shafts, moving the torque peak down to the normal rpm range used in aircraft installations, etc.
One question I had for the OP was why the RPM limitation on the prop is so severe. I think he said tip speed of 475 mph. Thats only Mach 0.62.
It is very common for props to run much faster than that. A 72" prop turning 2700 rpm is Mach 0.77. (Not the helical tip speed that includes the vector addition of the forward flight velocity). For cruise at 2400 rpm, its Mach 0.68. So why does the OP need to turn his prop so slow?
First things first...our propeller is 84", and we may opt for the correct 3/4 scale 96" propeller when it becomes available next year.
The 84" prop hits 475 mph (700 fps) at 3600 engine rpm, which is 1890 prop rpm. This is with a 1.9-1 reduction ratio. 475 is the tip speed cruise limit, where Mach .88 (+/-) would be a normal takeoff limit (red line) for tip speed.
In the RV world, it is likely not an issue as the diameter is normally smaller. But having a slower turning engine should be beneficial, and perhaps more efficient.
We have chosen the GM LS Hot Cam. It will give a minimum of 14% to 15% power increase. So the engine / PSRU / prop can all turn slower for the same power output. The primary benefit is being able to develop more power at altitude. At ten thousand, it is 189hp vs. 224hp. That is a significant increase, not to mention the added rate of climb.
Sea level numbers for the stock cam vs. Hot Cam are:
3600 rpm = 270hp
3600 rpm = 315hp
Comp Cams has an off the shelf model they recommended for us. It was more aggressive than the GM cam. Both cams were very close in power output from 3000 to 4000rpm.
Crane Cams told me..."Sorry, we have nothing for you."
The LS3 is an excellent choice for a number of reasons. Cost, reliability, and power. My friend has a SBC 327 LC9 in his plane. He uses 3000rpm for takeoff. It has gobs of torque! The acceleration is something else. But the LS3 will blow it's socks off!
Hope this helps shed some light on the process, and hope it is of interest to some of the folks here. I have never seen an RV with anything other than a conventional aircraft engine.
The above engine data came from GM Performance. Prop tip speeds came from:
http://www.warpdriveprops.com/propspd2.html