Head work (question ???)
 

I got 323 1.8 DOHC , the head is allready port and polished , but I want to mill it. How far could i go whit the mill? It's safe to mill it something more over .40? What is the safety margin whitout having belt tension problems or piston to valve contact problems?

How much Hp gain do I expect from this? ( rissing the Compresion)

Pd. ( Sorry if I got some erros... I don't speak/write english very weel...)

Mazda apparently is very conservative on this. They spec no more then 0.20mm (or 0.008"). There wouldn't be much compression increase from this little (about 0.1 increase). You can also grind 0.10mm (0.004") from the head. This hardly seems worthwhile when you can get 11:1 pistons from Mazda, or higher compression from elsewhere.