Another possibility is, if the engine has a head shim, remove the head shim for a small increase in compression ratio.

Some guys heavy into pylon racing send their engines off to be cryogenically frozen. It changes the properties of the metals and reduces friction. If that is allowable, it is worth checking into.

This won't help on an engine you already have but just know that all FP .40s are not created equal. It helps if you can hand select one with the best fit of piston and sleeve. Additionally, you would look for one that not only has a nice fit but feels ever so slightly gritty as you move the piston in the sleeve. These seem to seat the piston better. Also, a clean engine, without any varnish or carbon from castor will, all else being equal, turn a few more rpms. The engine will stay much cleaner using all synthetic fuels.

Here is another trick that worked extremely well for me. We used to race Fourstar .40s with the Supertigre GS .40 engine. I set my needle where the engine was running on the ragged edge of being too rich. All of the other pilots are tweaking their needles for just about the maximum rpms. What happens is that for the first two or three laps is that they would have a slight speed advantage over me but as the race continued, their engines would begin to heat up and lap by lap they would be slowing down while I picked up speed and became faster and faster because my needle setting supplied adequate fuel to the engine as it "unwound" in the air.

Another item that helps is the Tettra fuel tank which has a bag inside it to prevent the muffler pressure air from having any possibility of mixing with the fuel and leaning out the engine. As you may already know, as fuel burns down in a tank, the tendency is for the engine to run a little leaner. With the Tettra tank, you have a consistent fuel flow to the last drop without this tendency to become lean.

Just as all FP .40s are not created equal, the same goes for props. You can take say, 10 props, all the same make, diameter, and pitch, and one of them will give you more rpms than the rest. In pylon racing, every rpm makes a difference.

All of these things help out a small amount but collectively they can make a big difference.