Porting isn't difficult but it does require restraint. It's very easy to go overboard and actually reduce flow rather than improve it.
PRICE VS.PORTING
`It's the same old question that is debated daily. Everyone wants power, but few have the resources to buy those romantic CNC-ported heads with unobtainium valves that cost a bazillion bucks.
The budget solution has always been to pick the best original iron head and then do the porting work yourself, hoping for an improvement. But is that really the best way to go? We decided to find out. Last month, we assembled a very streetable 9.0:1 compression 466ci big-block Ford equipped with the Edelbrock RPM cam/aluminum head/intake package. The motor made a tire-roasting 565 lb-ft of torque at 4,400 and 514 hp at a leisurely 5,400 rpm. This combination was not bargain-basement but real-world using the stock crank and truck rods. So the question became, could we do a backyard port job on the stock iron heads and get them close to the Edelbrock aluminum jobs, or would the end result be cost-prohibitive?
We marched back over to Jim Grubbs Motorsports (JGM), tied up their SuperFlow 600 bench for three days, and basically made pests of ourselves in search of better flow numbers with the stock iron heads. We generated some minor improvements, but nothing to make Edelbrock nervous. The abridged version is that, at least with iron 429/460 heads, our limited backyard porting doesn't come close to the Edelbrock heads, and the cost to rebuild the stock iron heads ended up being within a couple hundred dollars of the cost of the lighter aluminums. Check out what we learned.
Porting at Home
The stock 429/460 iron heads in this story represent an interesting challenge. As with most Ford heads, the intake port is plenty generous if not a little on the large side. Conversely, the exhaust ports are horrible. Looking at the stock unmolested flow numbers, the average exhaust-to-intake (E/I) percentage for the stock exhaust port is a miserable average of 60 percent. The Edelbrock CJ 460 heads average a far superior 70 percent. These numbers direct us to work exclusively on the exhaust ports. It's true that we could crutch the engine with 10 to 15 degrees more duration on the camshaft to help the exhaust side. Our test last month proved the Edelbrock heads could use even more exhaust help since peak horsepower occurred at only 5,400 rpm.
We also discovered that the stock iron ports come with a 90 percent intake-throat diameter and 88 percent on the exhaust. This leaves very little material to blend into the valve-seat area, especially on the shortside or port floor. The only way to improve this situation is to enlarge the exhaust-valve size from 1.655 to 1.710 inches. This gives us half of 0.055 inch to work with, which still leaves precious little material.
The Ford exhaust port also includes an ugly square emissions A.I.R. injection boss inside the port just downstream of the valve stem that works as a wonderful flow impediment. This required about 15 minutes worth of tapering. With no prior experience with Ford heads, we improved flow slightly to increase exhaust flow and most of this was around mid-lift flow. But these numbers still do not come close to the Edelbrock exhaust flow numbers.