So i found a diy guide on how to port and polish in an old autosalon magazine. I've never done this before. Will it be beneficial to corolla? It has the 4A-F engine. What are the dangers if i get something wrong. Can anyone who has done this before give me some tips?

There's a bit of an art to an effective port and polish. Its the sort of thing I would probably get a machine shop to do so I know its done right.

If you grind away material that you shouldn't, you could open up a water or oil gallery which mean the head goes in the bin.

 

You won't hear ME say this too often ;) , but your best performance upgrade would probably just be to drop in a 4AGE, ZE or TE.

There's probably not a whole lot of point on a 4AF, they should have pretty decent ports to begin with. You'd probably only do it if you're also putting in big cams and changing the whole induction system. There would be easier ways to get more go first.

pretty decent ports? like as in nice and rough from the original casting.

 

There's plenty of people that home job this, but it's not just a matter of opening it as much as you want and yay, more power.

 

If you want to give it a very light touch and polish out the casting marks then sure, get into it.

When he says port, I'm assuming it means changing the shape of the port for a different function. A tidy up and a polish (that being a whole other argument) isn't really porting.