Machine work even just to restore a stock head to OE condition is not a budget exercise. It's often more cost-effective to invest in a set of aftermarket aluminum heads than it is to rebuild a set of stock iron heads.
The Price of Machine Work
The price of performance isn't just in the parts. It's also in the machine work. When you take a set of heads to your local machinist, keep in mind you're paying for more than just his time. Those trick machines cost a ton of money, and chances are your machinist is still making payments on them, not to mention the skilled labor necessary to perform all those precise machining operations. This work isn't cheap. The following are prices based on JGM's current rate. Other shops will certainly be different. Not all of these operations are required.
Chamber Mods
Most backyard porting heros overlook the combustion-chamber side of the head, preferring to work only on the port. The better way to look at porting is to keep the entire system in mind. This is true for both the intake- and exhaust-flow versions. For our big-block Ford, we worked only on the exhaust, but many of these concepts also apply to the intake.
There is a very slight radius in the Ford combustion-chamber wall adjacent to the exhaust valve at the closest point between the valve and the wall. Grubbs decided to open this distance to improve the low- and mid-lift flow. In order to save time, we didn't evaluate this change separately, but it appears this may cause a slight improvement in flow.
The stock seat also includes a clearly visible ledge or tiny trench just around the outside diameter of the valve. JGM feels this is a detriment to low-lift flow, so Grubbs used a cutter to lay back that ledge. In the test data, you can see that we lumped the chamber-wall modification, an enlarged throat diameter, the radiused outside diameter of the valve seat, and the radius cut on the valve face all into test 5 because of time constraints. This led to an improvement in low- and mid-lift flow but with no increase in high-lift flow. It's possible that certain changes cancelled others out or were detrimental to overall performance since we have no way of knowing how each change interacted with the others. If this sounds increasingly complicated, it's only because it is. Welcome to the world of cylinder-head modifications. Be prepared to be disappointed, because we thought all these changes would make this exhaust port really perform much better than it did.
This is the stock chamber area surrounding the slightly larger Manley 1.71-inch exhaust valve. Note the small ledge (arrow) just outside the edge of the valve. | 
JGM used a radius cutter to trim back the combustion-chamber wall away from the exhaust valve to improve flow while also removing the ledge that surrounded the valve just outside of the seat. |
Ford 460 Heads: Parts and Machine WorkDescription PricePerformance
valve job* $368.00Install guides 144.00Install hardened seats
144.00Convert to screw-in studs 172.00Back-cut valves, 32 degrees
64.00Intake valves, 2.08 Manley 103.60Exhaust valves, 1.71 Manley
170.00Guides, bronze wall 64.00Hardened exhaust seats 70.40V
alvesprings, Comp 84.88Retainers, Comp 59.99Keepers, Comp 24.88S
eals, positive-style Viton, Comp 33.95Screw-in studs, 716 inch, Comp
40.69Guideplates, 516, inch, Comp 46.39Total $1,590.78*Note: JGM's performance valve job includes cleaning and magnetic particle inspection, surfacing, facing the valves, honing the guides, and assembly.