Tom Wilson
July 1, 2003

Horse Sense:
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.

OK, we went for convenience when dyno'ing the Z304s. A carburetor, an electric water pump, and not much else allowed us to make our dyno date dead-line. Depending on the intake manifold used, you can expect maybe 10 lb-ft more torque and about 10 hp less when running injected. It's likely Z304 heads will be used on fairly seriously hot-rodded project cars, and this dyno setup is probably typical of many engines these heads will end up on.

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.

Bare Necessities
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.

If it wasn't for Steve Brule at Westech, we don't know what we'd do sometimes. Steve was the man when it came to putting the cylinder heads on the block at the critical last minute, and that meant a lot more than just screwing on the valve covers. Spring-installed height, retainer shape and diameter, spring selection, key availability, spring seat selection, pushrod length, and gasket fitment were all handled by Steve.

Next up were the pushrods, the pushrod guideplates, the rocker studs, and the rocker arms. Ford calls for 1.6 rockers, so we pulled a set of roller tip, roller trunnion, stud-mount, cast Comp Cams rockers out of stock. Using the taller of two rocker stud heights available, there was still barely enough thread engagement left for the rocker's adjuster with the rocker sitting at a workable height. This is apparently due to the +0.200-inch-tall valves the Z304 head takes in order to have the spring-installed height work out. Thus, with the tall valves the rocker arms have to ride quite high on the studs in order to have the correct geometry. A quick check with an adjustable pushrod showed a 6.700-inch length was the best compromise between rocker geometry and having enough threads left on the rocker studs.

Ford supplies guideplates with the Z304s, so there were no worries there. The guideplates do splay the rockers out slightly to accommodate the large valves and therefore slightly nonstock valve placement. This is no big deal, as all the geometry is taken care of by the guideplates.

With all that figured out, there was little left to do but bolt on the heads using ARP 1/4-inch bolts with 1/2-inch shoulders (takes care of the stock 1/4-inch threads in the block and the Z304's Windsor-style 1/2-inch head bolt holes). We dressed the engine with an Edelbrock Performer RPM intake manifold, a 650 Demon carburetor, an MSD distributor and spark box, our trusty Hedman four-into-one long-tube headers, about 4 feet of 1/2-inch-diameter exhaust pipe, and a pair of massive 3-inch inlet/ outlet Flowmaster mufflers. This is the standard Westech exhaust system, and from previous testing we know it not only clears the dyno, but it also costs no horsepower (even the mufflers).

GT-40X Heads
Because they had been set up and run several times already, the baseline set of GT-40X heads proved bolt-on parts for our 347. All we had to do was verify the pushrod length and rocker arm geometry, which all worked out fine.

Dyno'ing with mufflers is the norm these days. When you're running at full-throttle every day, all day long, everyone in the shop is happier when you keep things to a gentle roar. These massive Flowmasters and 211/42-inch tubing have proven no detriment to power production in repeated testing.

This brings up an important point. The GT-40X heads may not make quite the power of the Z304 castings, but they come assembled and are optimized for street use and street-oriented valvetrain parts. This makes them easy and inexpensive to get on an engine. The Z304 heads, on the other hand, require you to visit the machine shop first for a set of valves and springs and a bit of machine work. This allows selecting the exact valve and spring parts desired, which is a plus for the more performance-minded customer but is basically extra work for the bolt-and-go street guy.

As for cost, the Z304s look inex-pensive at $495 a piece, but once dressed with good parts by a com-petent machinist, they're more like $1,600 for the pair, ready to rumble.

Making Noise
Because we had been working with the Z304s all day to set them up on the short-block, we ran them first. A brief warm-up and some moderate-load running to help break in the rings started the fun. A quick power run up the tach to feel things out netted 414 hp, which we thought was a nice number for the first pull on our new 347 dyno mule.

A handful of minor jetting and timing tests followed. During the third of these tests, the power noticeably improved-about 10 hp-which was the new rings becoming friendly with the pistons and cylinder walls. It certainly doesn't take long for modern rings to break in. The 427 hp peak was reached just a pull or two later using 34 degrees of ignition timing and 76/80 jets in the Demon.

Coast's Street Fighter short-block does not come with a harmonic balancer, which is offered separately. The company carries the made-in-Australia Romac line, which is a traditional rubber-ring, two-mass design, similar to what Ford uses. We like its quiet operation and full, etched-in degreeing.

It was clear there was little left to do with the Z304 tuning because the power curves were smooth and beautifully shaped, and all the tell-tale numbers from the data recorder-airflow, fuel consumption, temperatures, and so on-were all excellent. In short, the combination was near textbook, and it was clear this combination of a Coast High Performance 347 Street Fighter short-block with its Pro Mustang cam combined with the Z304 heads would make an excellent, efficient street engine.

Next we pulled off the Z304 heads and set the GT-40X heads on. It's worth pausing here to say this went without a hitch, which isn't always the case with aftermarket parts. However, FRPP pieces always come out of the box with all the bolt holes drilled and tapped, and things go together like they're supposed to. About the only thing you could possibly label a hassle would be fitting the headers-they always require some grunting and leveraging to make the bolts, flanges, and mounting holes line up.

Dialing in the GT-40X heads was simple. Again, a couple of jet changes in the Demon to lean the combination three jet sizes did the trick. The best power of 403 hp came at 34 degrees of timing; best jetting was 74/78.

The Edelbrock Performer RPM with its just-right combination of torque and horsepower production proved a good match for both the Z304 and GT-40X heads. These are the GT-40X heads. We ended up running two different rocker arm packages, but both were full-roller, 1.6-ratio designs, so they were not a factor.

The only cautionary tale here was just a slight randomness in the power curve for the last 200 rpm right around the power peak. By no means excessive, this slight randomness in the peak number could have been the valvesprings just beginning to allow some extra motion. At any rate, the engine did put out 403 hp on two passes and laid down a string of 398hp pulls. We're going to use the 403hp figure in this instance as it did repeat. But if you want to be sternly conservative, figuring on 5 hp less certainly won't steer you wrong-counting on a little less never does.

The Modern Small-Block
With the 5.0 fleet now in the 100,000-mile category, the current well-turned-out small-block is a crate engine with a factory new block and everything else aftermarket. Our new 347 dyno mule engine is a perfect example. Detailed in our June issue ("Tech Mule," p. 75) our short-block is a $2,299.99 Coast High Performance Street Fighter. Built from all-new, stronger-than-stock parts, it has the basic architecture and specifically the right piston dome shape to accept many different cylinder heads and cams. With 347 ci, it's also representative of the latest breed of performance 5.0 Mustang engines.

The Probe pistons, with their dual valve reliefs, are key to accepting all sorts of large-valve cylinder heads. And, as forgings, these stout pistons will withstand the occasional "lean and rattle" common to dyno testing. With about 10:1 compression with most cylinder heads, they'll also work with real-world pump gas.

"Stout" also describes the bottom end. The crank is a cast-steel stroker with an extra 0.400 inch of swing and the physical durability required to live through constant dyno abuse. The block is a new 5.0 service unit, while the heavy-beamed 4340 connecting rods are another high-durability Probe item. Just to be sure, a 31/48-inch-thick steel Pro Mustang girdle is also on hand. Oiling is via a high-volume pump and Pro Mustang oil-pump drive.

For this Z304 head test, we used one of Coast's favorite all-around cams, a Pro Mustang 4017 grind. A hydraulic roller, it features 0.499/ 0.510 valve lift and 221/225 duration at 0.050 inch of lift on 108/116 lobe separation angles. It's designed to work with 1.6 rockers, which we used.

Now that we've tried this cam, we have to say it's a favorite of ours too. Combined with the 347ci displacement, it generated a bountiful, flat torque curve and a nicely arching horsepower curve to match.

Covering up the short-block are a Pro Mustang 7-quart front sump (early Mustang) oil pan and a new service part front cover. You'll need to add a timing pointer and a harmonic damper, as CHP sells the Street Fighter without one. We had Coast fit its in-house damper-a Romac. We then bolted the heads on with ARP shouldered bolts. They provide the 71/416-inch threads to fit the stock block, along with 11/42-inch diameter shoulders to work with the Z304 heads.