Jerry made up a fixture that attached to the cylinder heads cam mounts that allowed him to open the valves in a controlled manner while he flow-tested the heads.
A velocity stack was attached over the heads port opening to smooth out the airflow during testing.
Flow-testing cylinder heads is a very precise job. The vertical gauges on the left measure inches of water, while the horizontal gauges on the right measure airflow.
The cutaway of the intake port revealed two potential problem areas, if the porting gets too aggressive. The long side of the valve pocket (A) is very close to the water jacket, and the hump in the port (B) is close to the bottom of the lifter bore.
The exhaust-side cutaway also revealed a couple of problems. The water jacket and valve pocket have thin walls (A), and the valve-guide boss (B) protrudes into the port. Careful contouring of the valve-guide boss will be a big help here.
The turbulence vane (arrow) shrouds a good portion of the intake valve. According to the engineers at Ford, it promotes more complete combustion of the air/fuel mixture at low rpm (for lower emissions). The stock combustion chamber has a volume of 52 cc for a compression ratio of 9:1.
Jerry removed the vane and blended the area around the intake valve into the roof of the combustion chamber. This increased the volume of the combustion chamber to 55 cc which dropped the compression ratio to 8.77:1. The super-trick thing to do would be to weld up the chamber around the spark plug boss into a wedge shape.
The valve pockets were blended into the valve seat with a rotary file. Jerry didnt drastically reshape the pockets and ports; he blended them so the air would flow smoothly.
The combustion chamber and valve pockets were finished with a cartridge roll. He left the spark plug in place to prevent damaging its boss if he slipped with the grinder. He exercised great care to keep from nicking the valve seats.
The intake port was cleaned up and blended into the valve pocket. Because the port walls are so thin, Jerry didnt go in there with a rotary file, only a cartridge roll.
The exhaust port received the most attention. Jerry opened it up until it equalled the outline left by the header gasket. He smoothed down the valve guide boss and then blended everything with a cartridge roll.
A finished combustion chamber and valve pockets. Notice how close the valves are to the edges of the combustion chamber. You couldnt install larger valves even if you wanted to.
The finished intake port. There was no great trick to this work, just paying attention to detail.
The finished exhaust port is not substantially larger, but it is smoother and it has a better transition to the valve pocket.
The stock valves have well shaped heads. The intake valve from this used head had a fairly large deposit of cooked oil on its back side. This oil fouling happens during cold start up,when most engines have a little blow-by that condenses on the back of the valves. This condensation is then baked in place once the motor heats up. Over a period of time, this buildup will cut down on the motors breathing.
To minimize the fouling on the valves, Jerry had them polished. They were chucked into the output shaft of a 1,700-rpm electric motor and given a mirror finish.
The valve seats were given a three-angle valve job. And then...
The valves were hand lapped into place.
The finished combustion chamber with polished valves. This setup should add a few of the lost ponies back into our Stang.
When the Dearborn boys started putting the 4.6 two-cam motor in the '96 Mustang, our collective hot-rodding hearts sank. On paper, the trade-off from the 5.0 pushrod mill, to the 4.6 overhead-cam modular motor didn't seem to be that bad--we lost only 20 ci and we gained less valvetrain weight. But when the horsepower potential didn't seem to be there--there were no high performance parts (head, cams, manifolds, and so on) available--the future seemed bleak.
Ford SVO has jumped into the 4.6 scene with some really cool parts: a supercharger, high-flow intake manifold, exhaust head-ers, and cylinder heads. But what about the parts that make up the stock motor?
Well, maybe there's hope. In looking at the individual parts, it appears that the cylinder heads are the key to more power. By normal high-performance standards, the 4.6 heads are a sorry lot. The intake valve diameter is only 1.750 inches, while the exhaust is an anemic 1.340 inches. The ports are just as small--1.5-inches by 1.3-inches for the intake, and a 1.35-inch-round exhaust port. With a cylinder bore of 3.55 inches, there isn't a whole lot of room for larger valves.
The more we looked at these heads, the more we thought the valves and ports appeared to belong on a motorcycle. So to find out if there was any hope for them, we took them to Jerry Branch of Branch Flowmetrics; he has more experience in reworking motorcycle cylinder heads than just about anyone, so if anybody could help them, he could. After looking over the cylinder heads, Jerry said, "The best place to start is to flow-test the heads for a baseline and then saw one up so that we know what we have to work with."
The flow bench pointed up the head's shortcomings. The intake port flowed 208 cfm at .450 inch of valve lift, and the exhaust 140 cfm at .450 inch of valve lift; the measurements were taken at 28 inches of water. The valve lift was limited to .450 inch because that is the amount of lift for the stock camshafts. The valve springs had a seat pressure of 60 pounds and an open pressure of 150 pounds at .450 inch; these low pressures are acceptable due to the low weight of the valvetrain.
The cut-up head showed that any porting of the heads would have to be done very carefully. But there was a bright spot in the combustion chamber, in the form of a turbulence vane next to the intake valve. Jerry believed that if the vane was removed, it would unshroud the intake valve which would improve air flow into the combustion chamber.
After all the work was done, Jerry flowed the cylinder heads again. The intake flowed 250 cfm at .450 inch of valve lift, for a 20-percent improvement, and the exhaust flowed 158 cfm at .450 inch of valve lift, a 12-percent increase in flow. This should equate to about 25 hp. The power increase would be even higher on a motor that uses a blower. And since the aftermarket is finally starting to offer up some camshafts, there should be even more potential in the stock heads.