zipfast

iTrader: (2)

Ok say I have 1.94 intake and 1.60 exhaust valves.
How much clearance from the valve to the chamber
wall is considered good or NOT shrouded?

five7kid

iTrader: (14)

Per http://www.sa-motorsports.com/diyport.aspx Step 5:

"Exhaust valve "shrouding" occurs when, at high valve lifts, exhaust flow is impeded by the closeness of the chamber walls to the edge of the open exhaust valve. Shrouding is common with pre-1971 Chevrolet small- and big-block V8 and early 289/302 Ford Windsor heads. At .300-.400 valve lift, there should be 3/16-in. or more between the edge of the valve and the adjacent chamber walls. If you do lack 3/16-in. clearance and there is material between the edge of the chamber wall and the gasket opening scribed on the head; remove material along the chamber wall such that exhaust valve shrouding is reduced. Only remove material inside the scribe line and only enough to achieve the clearance."

zipfast

iTrader: (2)

Thanks Five7, that's just what I wanted to know.

Damon

Yep, good info. I was always told that 1/8" was marginal and that 3/16" was good.

1989GTATransAm

iTrader: (3)

One other thing is the intake valve diameter should not be larger than 52% of the bore. This will help prevent shrouding.

jamon8

iTrader: (3)

what about on the intake side

I put 1.94 valves in my 305 heads and wanted to know

F-BIRD'88

You have to take "valve shrouding" with a big grain of salt.
The airflow thru the intake port and into the chamber is biased to the common wall side and roof of the port. it curves toward the spark plug as it enters the chamber. Squirt some water with the garden hose in the port to see the flow pattern. This is the high flow area. This is where you do your "deshrouding" to get flow. The area around the valve that appears to be shrouded is actually a low flow area anyways. The airflow does not flow thru the port and into the chamber then take a right turn into the cylinder wall. You do not need to get all carried away releiving the chamber around the valves.
Your new valves is .050" larger in radius than the old valve. So you only need to relieve the chamber around the valve by .050".
The head gasket is a lot lot bigger than the cylinder bore. Do not grind out the chamber to the gasket. You won;t gain any flow and just weaken the head. To fit the new valve in the chamber use the old valve and select a drill bit that just fits between the partially open old valve and chamber wall. the drill bit is your guage. Now using the new larger valve and drill bit see how much and where to grind the chamber wall. .050" large valve radius= .050 larger chamber walls. No need to get carried away.
The black line in the second pic shows where the valve is shrouded.

F-BIRD'88

high flow pattern in intake port and into the chamber towards the plug

1989GTATransAm

iTrader: (3)

Jamon8. From what I have read you are right at the maximum. However just adding a larger valve is part of the equation. Proper head porting and valve seating angles plays big part of it.