They also do a little massaging in the exhaust valve region by jumping from the stock 1.550-diameter two-piece stockers to 1.60-diameter one-piece forged replacements from Manley (PN 11365). While both valves share 0.311-diameter stems, the stock valves have a flow-hampering 0.382-inch fat section beneath the tulip (pen points). By contrast, the Manley stainless valves go the opposite way. Thanks to an undercut, the stems reduce to 0.305-inch directly beneath the tulip for better flow. Also note the swirl polished texture. Going to 1.60 diameter exhaust valves doesn’t require seat removal – just a simple cut to suit the added head diameter – and delivers an extra 3-7 percent flow capacity.
Here’s a trick Fred performs on most exhaust valves, regardless of engine type or application. Using a simple flat file, he contours the edge of the valve face to break the sharp edge. It only takes 20 seconds to do each valve. A careful rolling motion and medium pressure are what he uses.
The pen points to the rounded edge after the filing trick. Fred says the new shape makes it easier for pressurized exhaust gasses to flow around the valve head and out the port. The abrupt contour found on most unmodified valves (left) is more likely to cause the gasses to shear and slow progress. Net gain to the total flow figure is about 1 percent.
