I'm thinking about putting some 2.02's in my double humps and I remember reading one time that factory 2.02" heads had little notches in the combustion chamber that un-shrouded the big valves. Does anyone have a picture they can show me? I'm also wondering if unshrouding the valves will be worth more than the loss in compression!?

Originally posted by 19Nova72:
I'm thinking about putting some 2.02's in my double humps and I remember reading one time that factory 2.02" heads had little notches in the combustion chamber that un-shrouded the big valves. Does anyone have a picture they can show me? I'm also wondering if unshrouding the valves will be worth more than the loss in compression!? =
Small blocks don't need the notches but it does help on 4" bores to "roll" the edge of the chamber to the gasket a little on the intake.
The biggest deal is to be sure the head is unshrouded to the gasket on the intake & the throat is done correctly under the valve or you can lose up to 20cfm of flow which is probably not what you have in mind :D
You basically want a 60 degree cut about .080 to .100 wide under the seat in most applications on the intake.
You do this with a 70 to 75 degree cutter in the throat area. This will leave a "ledge" on one side in the bowl which you should grind out assuming no rules disallowing grinding ( lot of circle track deals)
On the top you want 30 to 35 degrees above the seat for about 25 to 50 thou or so followed by a 15 degree cutter that has a radius edge that goes to the side of the chamber out to the gasket line.
Do not take the sharp edges off of the different angles.
You also want the valve backcut about 30 degrees to take the 45 degree seat edge off.
The ex should be a full radius off the seat into the throat & bowl & the top will like 35 to 38 degrees followed be a 10 degree cutter to unshroud the chamber.

Piece of cake,, you can do it in your garage with just a few stones & your dremel :D
Just kidding, there is a little more to installing large valves then just cutting or grinding seats & this was the short version ;)