Here is what lapped valve seats look like. They do appear to be a bit dull in finish. Of course!
They have been ground on very gently, and with a very fine abrasive grit compound. The result is a very uniform and air tight sealing surface between the valve and the seat. It is good enough to hold water.
The exhaust seat is wider than the intake seat. Because the exhaust valve runs a lot hotter than the intake valve. The seat conducts heat away from the valve head when the valve is closed. The wider seat helps conduct more heat.
The SOHC head comes with the valve seats ground at three angles. The valves are done primarily with a single angle cut. I did not depart from that format and go for a five angle cut on the seats, nor did I go for a three angle cut on the valves.
I lap the valves in to end up with valve seat contact surfaces that are on the high half of allowable widths: so the valve heads can shed heat better. I do not remove any more material from the valve seat inserts so that they can have the best chance of remaining stable and located; and not become a hot spot.
Increasing flow via camshaft change is the way to get more flow without sacrificing durability. A larger and more efficient turbo and exhaust system will also help.
The valves and seats are the hottest things in the combustion chamber. The intake valve is cooled somewhat by the incoming air/fuel mix; in conjunction with the valve seat. Reducing the heat transfer via the seat only puts more heat into the incoming air as it passes around the intake valve head: that does not help performance. The exhaust valve head is cooled primarily via the seat face contact. Reducing the heat transfer by narrowing the contact surface area elevates the valve head temperature; and that could become a source of pre-ignition.
I realize that many believe that NOT going with the five angle seats and three angle valves is stupid.
IF this were a NA build, then I might agree.
BUT, this IS a boosted build.
The heat load that the head and valvetrain sees and will see while boosted is considerably more than what a NA motor will ever see. My priority is durability and reliability first.
For more flow.....well, that's what that turbocharger is there for.
ADDITIONAL: Lapping compound IS an abrasive compound. You DO want to make sure that there is no residue left on either the seats or the valves....
....that is what hot, soapy water and a toothbrush is for.
....you CLEAN the head thoroughly with hot soapy water; scrub thoroughly the valve seats with the toothbrush, and rinse the head off repeatedly until it is REALLY clean.
[and you do the same thorough cleaning to the valves]
THEN, you can start the assembly process.