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.