This weekend?
£500 isnt going to get you much, and thats assuming your not including removal/fitting costs.
There are big gains to be had on the 172/182 head, however application is more important. If your running the stock inlet manifold setup, then any work carried out on the cylinder head is severely masked and gains are minimal.
As an example, my development program from a few years ago resulted in me being able to attain an 8% raw flow gain over stock with just one of our CNC valve seat jobs (none of this 1974 '3 angle' stuff), which provides great value for money.....however if you stick it onto a stock engine the gains are virtually nothing due to the inlet manifold.
Also the head requires quite some substantial amount of work to make modification worthwhile. The portshape as it is standard flows well enough, but you just dont have the material in the right area to modify it to a shape that provides an optimum port shape. If you just get someone to 'open' up the ports then the flow bench might register a bulk gain in flow, but that rarely is what we are looking for nowadays.
Relying on straight flow gain data is the wrong way to go about modifying a cylinder head.
The F4R is tricky and traditional methods dont work well.
