If you've been keeping up with us on a monthly basis, then you'll surely recognize our '89 Mustang project mule from last month's test of the new Nitrous Express NXL system. While we proved that nitrous is the great equalizer for underpowered V-8s, we also learned that regardless of the number of bolt-ons you have, you're only going to make as much power as the most restrictive part of your engine combination will allow.
| Twisted Wedge Flow Chart |
| Lift Value | Intake Flow (cfm) | Exhaust Flow (cfm) |
| 0.100 | 63 | 53 |
| 0.200 | 141 | 107 |
| 0.300 | 205 | 144 |
| 0.400 | 233 | 171 |
| 0.500 | 251 | 187 |
| 0.600 | 251 | 193 |
|
| Note: Peak of a stock E7TE head is about 150 cfm @ 0.500 (int.) and 113 cfm @ 0.500 (exh.). |
Case in point, our Mustang's 5.0L V-8 had been previously outfitted with a ported Ford Racing Performance Parts (FRPP) Cobra upper manifold, a larger 65mm throttle body, a massive Granatelli 80mm mass-airflow sensor, a Crane Cams 2040 emissions-legal cam (220/220 duration at 0.050, 0.498/0.498-inch intake/exhaust lift), and FRPP 15/8-inch shorty headers along with a complete 21/2-inch exhaust system. But it was all pumping through a restrictive set of factory E7TE cast-iron heads with 1.72/1.46 intake/exhaust valves.
| Peak Dyno Numbers |
| hp | lb-ft | Change |
| Baseline | 213 | 263 | n/a |
| TFS Twisted |
| Wedge | 264 | 307.5 | +51/+44.5 |
We knew we had the potential to make a decent amount of power with the listed aftermarket goodies, and our baseline chassis dyno numbers revealed a respectable 212 hp with only 265 lb-ft of torque at the rear tires. Would a simple head swap be the final step that would turn this mild 302 into a robust boulevard brawler? There was only one way to find out.
| Track Results |
| Density Altitude | 60-ft | 1/4 e.t. | 1/4 mph | change |
| Stock heads | 200 feet | 2.5 | 15.8 | 95 | n/a |
| TFS Twisted Wedge |
| and Nitto NT-555R |
| Extreme Drag Radial | 3,432 feet* | 2.1 | 14.2 | 99 | -1.6/+4 |
|
| *Tested at Los Angeles Country Raceway, corrects to 13.6 at 102 mph at sea level. |
We paid a visit to the performance tuners at X2C Motorsports in Van Nuys, California, to began our experiment. Our heads of choice were a pair of out-of-the-box aluminum Trick Flow Specialties Twisted Wedge assemblies featuring 2.02/1.60-inch intake/exhaust valves with 61cc combustion chambers. The Twisted Wedge heads maintain the engine's stock 9.2:1 compression ratio, retain all the OEM-type accessory holes, and are a 50-state emissions-legal high-performance replacement for '88-'93 5.0L Mustangs. That means it'll get by the smog police with a very big Green Peace-style thumbs up. The bolt-on was simple, and we're happy to say the performance difference was staggering with a gain of more than 50 rear-wheel horsepower. Our little 302 now produces enough grunt to get us into trouble with the local authorities. Read on for the juicy details!
Swapping heads on a late-model fuel-injected motor may seem a little intimidating at first, but you'll find that the idiot-proof factory electrical connectors and fuel fittings only go back together one way, making it easy to figure out where they need to be attached.
The front accessories, including the A/C compressor and power-steering pump (along with the brackets), will need to be removed. Keep in mind that if your A/C system is charged and functional, you should not disconnect the lines, but rather swing the compressor and its lines out of the way toward the passenger side of the engine bay.
Once the upper manifold and accessories have been removed, disconnect the fuel system's feed and return lines and remove the distributor. Depending on how well the lower manifold is sealed, you may need to use a pry bar to remove it. If so, place the pry bar above the water pump and below the thermostat housing and gently lift the manifold.
To remove each head, simply unbolt the rocker arms and remove the 10 head bolts. When lifting the heads, be sure to have a good grip on them, as these portly stockers weigh nearly 50 pounds each.