I have not tried this on the 4.0, but in most cases the intake passages are best left as cast to retain some turbulence to keep the air-fuel mixed well. The point where performance can be gained is in matching the size and shape of the manifold-head juncture. Go ahead and polish the exhaust ports, but don't make the port too big or you will lose velocity.
Yeah, but as i read on they say that porting with a ruffer grit it better, Like its better to port with a ruffer cut then a polish,, Theres so many opinions out there lol ill just have to keep reading and get more opinions
You polish the combustion chamber and the exhuast port, just open everything else up.
To get to the 40hp mark you need to do more than a gasket match. Porting is a skill at least if you plan to make horsepower it is. There is a reason places charge 1600 for a set or ported and polished heads.