I took a Webra .50 that was already a very strong performer and turned it into a fairly high speed engine.
The key is to start with a very free but "tight" lower end. I used the best Swiss made bearings rated for this application. The crank should be a snug fit into the inner races and of course the case needs to be heated to 350 degrees or so for the bearings to drop in place.
The exhaust port [open] timing is increased to 180 degrees, the closing edge of the crank's intake is moved back to about 60 degrees, the crank's "tunnel" is increased by patient sanding drum work until it is as big as you dare take it to increase air handling capability.
I made a 10 or 11 mm venturi and placed the carburetor in storage.
The crankcase is tapped to supply pressure to the fuel system.
The engine uses a very short Mac's header and tuned pipe.
This combo is tuned for 7.5 x 8 props and it will pull a Diamond Dust or Screamin' Demon delta in the 170 mph range without getting hot. on 15% nitro.
I've taken APC 8 x 8s and chopped them down for cheap props to break.
Once you increase the timing to 180, that liner will only be useful for small speed props, so you are making a commitment when you decide to modify an engine to this degree.