Do not believe the thrust numbers you see on the RCShowcase website! They use this little program to calculate that... and this little program doesn't even take prop pitch into account when calculating thrust. So it shows the same thrust for (example) a 20x8 at 8000 and a 20x12 at 8000... Go figure

Two different engines turning the same prop at the same rpm will generate the same thrust.

The ZDZ 80 twin and single engines will be close... I would be very surprised to see that much of a difference between these two engines on the same prop.