Hey Johnny,
I'm Maurice and I have the same problem you have had in the past. What did you do about the 6800 RPM and loss of power problem?
Mine just started doing the same.
Maurice
925-595-1111
check your intercooler, if its not winterized properly it may develop small cracks and actually burn water and gas resulting in incomplete combustion and thus a loss of power as well.
Intercooler leaks are not common but certainly lethal and invisible from the outside.
Remove the plugs after a run and check inside.
Reason for low revs
1. old plugs, bad spacing, consider getting iridum plugs, NGK DCPR8EIX or denso IXU27 or IXU24
2. overfilled oil (plugs will also be oily, should be a cream color)
3. leaky supercharger tubes (check clamps and hoses on all intakes)
4. Old supercharger washers, you will have to check PSI on full boost, superchargers need a rebuild kit at 100 hours, the kit is about 300$ if you do it yourself in parts
Note you will also get some vibration if your engine is combustion water (small amounts). If the leak is bad you will blow a valve or rod
PS your max redline on an RXP should be around 8050 RPM with the stock impeller. Upgraded impellers will reduce the RPM if the pitch cannot be pushed by the engine mods (ie 14/19 solas on a stock rxp setup will reduce RPM). You would just need more mods, most HP to push a higher pitch prop. Stock is around 13/18 pitch.
Cheers
C