Those are from my old Chrysler Conquest I ported and polished at home. Worked beautifully.
My opinion with the exhaust and chamber is to make it shine like chrome. My theory is to try to retain as much heat as possible to drive the piston down the bore. They say that you only use 1/3 of the heat energy in the fuel to actually move the car, 1/3 out the exhaust and 1/3 to the cooling system.
The heat the the cooling system is where you can gain. by polishing the chamber and the exhaust side you lessen the surface area that heat is able to transfer through, there by increasing the work the heat can do. Granted there will be more out the exhaust side, but that we can call a byproduct of the added work.
Now I don't know how well this may work for a N/A vehicle (the Conquest was turbo'd, factory then upgraded), but I'd imagine and improvement in efficiency will yield power gains and possible some economy gains. I do plan on putting my thoughts to the test and am working at it slowly as I just acquired a test subject.
Very time consuming, and yes its difficult. The motor has to come apart, drop all the valves and keepers, and then go to work.
It can have some good gains, but you can only go so far without some serious knowledge of what works and what does not. You cannot risk reshaping the ports without the right tools and knowledge, BUT you can smooth things out and improve some flow a bit. Alot of work to just go after that. If it is apart already, then it may be worth the time , if you have the free time and a good steady hand.
oh is it really that difficult? dang. i was just going to take off my exhaust manifold, mark out the ports and grind/polish away until they're the same shape/size as the exhaust entrance. i wont be touching the chamber as i dont wanna remove the head or anything.
If you are not taking the head off, don't bother. Metal shavings can do serious damage to your engine and no matter how hard you try odds are you will leave something behind and it will come back to haunt you.
ah bugger this turns out to be much more complicated than i assumed. i figured it would be an "exhaust header off - grind - header back on" sorta thing. guess i'll just port the throttle body for now. i think i can handle that one.
Good Porting takes alot of practice. good to have a caliper on hand. There are basic DIY porting kits out there for decently cheap. pic up a spare head and practice doing it. once ur confident, then if you ever have time, use ur good head and get to work. It's not really worth it unless you do a serious NA build or go w/ some boost though.