When working with ally you want proper tungsten bits, a selection of sizes and shapes to create the port bends and angles you need for correct flow. Using hard metal burrs with hatched angles will see you getting it clogged up fast and getting nowhere after about 30 secs. And drill speed isnt really what i live to use as you can catch a nick with the edge of the burr and rattle it about in the port, wrecking it, since you will need to take your eye off the burr to switch off the drill.
As for resin casting, dont bother, your not getting into totally redesining a port. And itll jsut be cheaper to do a differnt port design on each cylinders inlet and exhaust, then get it tested if you wish, then copy that onto a new head. They can be had for about 15-20 quid.
Dont go just increasing the port size to the size of the gasket, that will see you gaining no power at all and just loosing a nice dollop of torque at lower rpm.
The most important part that you need to concentrate on in DIY porting is the 3/4" below the valve seat. Youll need ot remove the valve guides to get the desired shape. Im not about to divulge my work so cant go into too much detail.
But basically, just smooth it up and create as smooth a constant radii as you can on the floor and roof.
With the manifold side of the port, just remove the casting marks and the rough finish and end up with a 120 or so grit finish, do this in the inlet manifold aswell. And the manifold responds well to reshaping aroung the TB base and where each runner seperates just under teh TB. Dont forget to match either.
Get the seats cut in at least 3 angles as this will see the majority of your easy gain. backcut the inlet valves and cut a flow reversal edge on the exhaust valve.
This basic work should see you a decent gain if you do it properly.
But since your just mucking about just have fun.
Bigger valves are useless at this point and cost far too much.
As i said before, just enlarging will see your head going...ffffffffttttt......instead of brrrrrrrrrm
