Steve Baur
Former Editor, Modified Mustangs & Fords
June 1, 2008

Step By Step

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Ford Racing Performance Parts' GT-40X Turbo-Swirl heads (M-6049-X306) retail for just under $1,200. We also ordered FRPP's polished valve covers (M-6000-F302), high-performance gasket kit (M-6051-A50), ARP head bolts (M-6065-D289), and hardened pushrods (M-6565-L302).
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The combustion chambers measure 64 cc and feature 1.94-inch intake and 1.54-inch exhaust valves.
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The GT-40X Turbo-Swirl heads flow 240 cfm at 0.550-inch lift through the 178cc intake runner, and 170 cfm at 0.500-inch lift out the 62cc exhaust runner.
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We began the cylinder-head swap by disconnecting the negative battery terminal and then removing the upper intake manifold.

Not one to forget our roots, MM&FF offers yet another 5.0L-themed tech article for you to get your mitts on. This month, we're modifying a 5.0-/AOD-equipped notchback with a set of cylinder heads from Ford Racing Performance Parts.

If you've read the last several issues, you'll remember that this slick, black coupe is no stranger to these pages. We began by installing a Nitrous Express nitrous-oxide system, and followed that up with a bevy of bolt-on hardware that has helped us slash quarter-mile elapsed times and increase horsepower and torque.

For the most part, we've been verifying our progress through dragstrip testing, with the exception being the last article, in which the Florida seasonal track closures forced us to hit the dyno. While we were there, we took advantage of having one of the best tuners in the country, HP Performance's Tony Gonyon, burn a custom chip for the coupe.

This month, we went back to HP Performance in Orange Park, Florida, as we figured the GT-40X Turbo-Swirl cylinder heads should produce a sizeable gain in power. We were also anxious to get back to the track to see what times the little juiced coupe was capable of with all of the new speed parts that we added.

Before all of that happened, though, we opted to address a few things, such as the tire situation. At the track, we found the 245/50/16 Nitto drag radials we had mounted on the stock Pony wheels weren't enough to handle the 150hp nitrous hit. With that in mind, we called Nitto for something a bit wider, while at the same time, our coupe's owner upgraded the wheels. The new Saleen Fox-body replica wheels from Wheel Replicas measure 17x9 inches at all four corners. With the larger wheel package, we stepped up to Nitto 275/40/17 drag radials out back, and paired them up with a set of 255/40/17 Nitto 555s up front. Weight wise, the new package is about a pound heavier at each corner, so unsprung weight isn't greatly affected despite the sizeable increase in wheel and tire size.

About the same time, our car owner scored a deal on some suspension components that should help the coupe plant the power more effectively. A package deal for a few hundred dollars netted UPR chromoly rear lower control arms with urethane bushings, Lakewood 50/50 rear drag shocks, and Strange Engineering 10-way adjustable drag struts.

Installation of the cylinder heads took a little more than a day to complete. When we get involved in a build like this, we end up detailing many of the components, not to mention the engine area, and this takes a little more time, as do those runs to the parts store. We've covered in-depth cylinder head installs before, so this time around we centered on the particulars of the swap as well as the results.

Here are a few tips. Make sure you have intake plenum gaskets for your particular intake before you start, especially if the intake is aftermarket and has been on the engine a while. If you're doing away with the smog setup (illegal to do on a road-going car, by the way), including the thermactor bypass at the back of the heads, make sure you order a set of threaded insert plugs to fill the holes in the heads. A small propane or benzene torch comes in handy in removing rusty and/or stubborn bolts and plugs. Don't lose the factory dowel pins that keep the cylinder heads located on the block, and make sure you have the head bushings for the cylinder-head bolts, if applicable. You'll also want to make sure that the deck surface is immaculate before dropping the cylinder heads onto the block.

Header bolt removal can be a pain with aftermarket headers, especially considering that you can't usually get a socket on the end of the bolts. Just grab a pair of wrenches, loop the larger one over the smaller one, and let leverage do its thing. You can also use two small wrenches, hooking the box end of one on the open end of the other.

Once the heads were bolted on the car, there was an immediate seat-of-the-pants difference in performance. Our slugomatic AOD Mustang now finally feels like the quarter horse that it is, and HP Performance's Dynojet dynamometer showed we had picked up 24 hp and 22 lb-ft of torque at the rear wheels. This put our coupe at a total of 265 hp and 303 lb-ft of torque on muscle alone. HP's Tony Gonyon noted that the same combination with a manual transmission would produce about 30-40 hp more. We were happy with the results, and even happier once we cracked open the nitrous bottle and let the happy gas loose. With the Nitrous Express system delivering 150 hp worth of nitrous, power output jumped to 378 hp and 486 lb-ft of torque at the wheels. All of that torque was available by 3,500 rpm, too.

Having used HP Performance for previous Fox-body tuning, we knew we'd be logging each dyno run using the Race Systems SnEEC-IV real-time datalogger. We're glad we did too, because the SnEEC-IV revealed that our stock 19-lb/hr fuel injectors were seeing a 98 percent duty cycle, which isn't exactly safe since fuel injectors can lock up when run wide open. Since our nitrous system is a wet system, the added fuel comes in through a fuel solenoid, and it turned out that the tune-up is actually safer on the jug.

The power numbers from the dyno looked great, but what we really wanted to do was get it to the track. Heading to Bradenton Motorsports Park in Florida, we arrived with the nitrous bottle full, intent on slaying our previous best elapsed times of 14.55/97 mph on motor and 13.04 at 112 mph on the sauce. With the extra horsepower from our last few rounds of bolt-ons, we ran a 14.13 at 100 mph.

The front dress, including alternator, A/C compressor, power-steering pump, and accompanying brackets must be removed before you can take off the heads. Follow these with the removal of the distributor, upper and lower intake manifold, and valve covers.

Our available track time was coming to an end, so we cracked open the Nitrous Express bottle and heated up the hides. Our black notchback responded with a 12.89 at 114 mph--better than our 13.04, but we heard the rev limiter at the 1-2 shift and knew it killed some e.t. The AOD was taking so long to shift that moving the shifter at 4,000 rpm still allowed the engine to tag the limiter at 6,000.

For the next run, we shifted a tad earlier, and the car quickened to a 12.69 at 115 mph. For our final run, we left the shifter in Drive and let it do its thing. The transmission shifted at 3,500 each time, and the Pony charged to a 12.68 at 115 mph. It would've been a faster run had the tires not spun at the nitrous hit.

Next month, we'll install a fully built AOD from the folks at TCI, along with one of their higher stall-speed torque converters. Quicker shifts will help elapsed times as will the high stall speed, which should get us into the nitrous sooner. We'll also take care of the maxed-out injector issue and step up to a slightly stickier tire package, so stay tuned.

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