you can try an x460/3 blade,this gets the back end to lift a bit and not seem so sluggish,plus it will allow the engine to "wind out" as nitro engines love to do,,,I believe the person you bought the engine from is right that it's output is around 6hp. I'm not sure but it looks like your engine was slightly modded from the external views you provided...(lightened flywheel,and head tapped for water exit) looks like he had that engine in a rigger before,I started a thread awhile ago asking the power losses involved in plumbing a tuned pipe into a quad exhaust and most of the replies agreed that power loss would be minimal.....if any.......[:-]