Ford Racing Performance Parts' Z304 Head - True Power
We Hook Ford Racing Performance Parts' New Z304 Heads To The Horsepower Polygraph And Find They Aren't Lying
The Hedman long-tube headers with which we tested the Z304 heads and 347 engine combination have to be one of the more tested sets of headers in the Ford world. This same set of headers has been collecting hot air for us since the mid '90s when we began testing at Westech. We think they've been on every small-block we've ever run there.
Last month we introduced Ford Racing Performance Parts' Z304 cylinder heads ("Draggin' Ball Z," June '03, p. 50). The buzz on these was centered on their low cost and gung-ho power production-a noticeable gain in aggressiveness in a stock-architecture cylinder head from the engineers at FRPP.
This month we put those claims to the test by bolting the new Z304s to our equally new 347 dyno mule and giving them the ol' trial by open throttle. The results were good, with 427 hp showing up with a streetable cam, a small carburetor, and excellent efficiency. So, for now, let's say the Z304 head is certainly a capable unit.
As the 347 test mule was new to both you and us, we wanted to provide a baseline using commonly available and well-known cylinder heads. That was easily done by bolting on a set of stock GT-40X heads Westech had on hand. The quick news is these aluminum GT-40X heads gave up 24 hp to the Z304 castings.
Before we could dyno the Z304s, we obviously had to assemble them with valves, springs, and so on. Our intention was to use exactly the hardware Ford specifies, so we consulted the data sheet that came packaged with the cylinder heads. It called for Manley 2.02x1.600-inch valves and several part numbers worth of Crane valvesprings, retainers, keepers, and valvespring seats. After a few phone calls, Manley and Crane supplied us with the parts, and we were ready to go.
In the meantime, the heads were sent to Dougan's Engine & Machine for the required valve seat grinding and, as it turned out, valve guide honing. This is detailed in our June story, as referenced earlier, so we won't plow that ground here, other than to say the valve seat grinding is prominently listed as required by Ford. There was no surprise there, but having to hone the guides to get rid of some taper was. Nothing really out of the ordinary, Dougan's assured us, as many new heads require a bit of guide finishing before they're just right. Overall, Dougan's gave the Z304s high marks for general finish and machining accuracy-just what we've come to expect from FRPP.
As you've already guessed, when we showed up at Westech to put the heads together, not all those springs and things were compatible. The Manley valves were fine, but the valvesprings were 600-pound monsters ideal for Pro Stocking a Caterpillar, but totally unsuitable for our moderate hydraulic-roller cam. Luckily for us, Westech is heavily supported by Comp Cams, so a large supply of its valvetrain parts are on hand for just such deadline emergencies. With no time to go back before our dyno pull, we raided the Comp gear and came up with PN 929 valve-springs, Comp retainers and locks, and some oh-too-thin shims to function as valvespring seats.
A noteworthy aspect of all this was the valvespring that best matched our cam was out of stock at Westech-how could it be any other way-so we had to go up a step to accommodate the large, somewhat-out-of-phase, 1.55-inch-wide spring pocket on the head, and the relatively mild 0.500-inch valve lift and 220-degree duration at 0.050 inch of the cam. In other words, Ford has the Z304 head set up to accommodate racing-style large spring diameters for hot-to-trot tuners, but we had a more streetable camshaft that didn't require so much spring.
We ended up with 180 pounds of seat pressure and 380 pounds over the nose of the cam. That's a bunch, about the limit for a hydraulic-roller cam such as ours, and we were concerned this might cost us some horsepower. It turns out we didn't need to worry about that.