[Arragonis]

You need more torque not hp - hp is a function of maths :

hp = (lb/ft * rpm) / 5252

Torque is the twist your engine makes when you press the go pedal. To get more torque throttle bodies will not help much. Not even if you got superbike ones. Superbikes don't need much torque so they just rev higher.

To get more torque you have three choices in order of difficulty :

1. Buy / borrow / rent a tow barge - truck, car, whatever.
2. Add a turbo - turbo means more torque at lower engine speeds.
3. Convert to Diesel - unlikely to work unless you want to restrict yourself to ~50mph due to the lower redline (4K vs 6.5 in the Petrol)

If you go with 2 or 3 you will find the clutch is no longer your friend as it wasn't designed for the level of torque being produced. It also probably was not designed with towing either. 2 will also require reworking to the FI system and maybe some head work to reduce the compression ratio. Option 3 I think has only been done with a Kubota which is not a car engine and won't work well.

Go for 1, it makes sense.