Kristian Grimsland
Associate Editor, Muscle Mustangs & Fast Fords
March 9, 2014

By now, you might have taken notice of our little green Fox. It's received a few minor cosmetic and functional upgrades over the past couple of months, and for power, we dropped in a new reproduction 306ci Economy short-block from LatemodelRestoration.com. It's been a work in progress and we've been looking for ways to improve its potential on the street. For this issue, we turned towards the engine's induction.

When we overhauled our Fox, we installed a set of aluminum Pro Action small-block Ford cylinder heads from Racing Head Services, an Extreme Energy Xe276HR camshaft, and reused its old BBK 65mm throttle body and Cobra intake. When strapped down to our in-house Dynojet dyno, it laid down 290 peak rwhp and 318 lb-ft of torque. It was a stellar improvement over the previous setup, and we saw gains of 47 rwhp and 21 lb-ft.

In a constant search for power, we wanted to improve airflow. We knew our Cobra intake was holding us back, so we conjured up the idea of an intake test. After tossing around ideas of which intake to choose, the idea of an intake comparison came to life. Edelbrock Performance has been in business for over 75 years and offers a variety of intakes for pushrod 5.0L Mustangs. Two of its most popular intakes for 5.0L Mustangs are its Performer (PN 3821, $629.97) and Performer RPM II (PN 7123, $619.27) intakes, so we chose these. Each intake offers an increase of airflow, but in a different rpm range.

"The Performer intake is a great upgrade from stock and is 50-state-legal," Technical Sales Coordinator Smitty Smith of Edelbrock told us. "The Performer offers a substantial increase in the lower to mid-range powerband and is good up until 5,500 rpm. We've seen gains of up to 37 horsepower over stock and or close-to-stock applications."

The Performer 5.0 RPM II intake offers gains in the 1,500 to 6,500 rpm range, and is more suited for vehicles that see both street and dragstrip use. This manifold features a larger plenum, and a V-shaped crossover with an increasing cross-sectional area, which passes over to eight large tapered runners.

In order to complete our test, we turned to Sinister Mustang for our manifold needs. Sinister is one of the newest competitors in the Mustang aftermarket, and offers a wide variety of aftermarket parts for your Mustang. Sinister offers a full line of top name-brand products, including SCT, Steeda, Ford Racing, BBK Performance, Edelbrock, and more.

With our intakes in hand, we headed to Ramsey's Performance of Lutz, Florida, for our first manifold install. Technician Ryan Frazier led the way and installed the Performer intake in a few short hours. We also had Dennis Ramsey, owner of Ramsey's Performance, burn us an SCT Eliminator chip (PN 6600) once finished. After the install, we headed back to our Tampa office where we strapped our little green Fox to our in-house Dynojet dyno. Our Fox cranked out 300 peak rwhp and 337 lb-ft of torque. That's an increase of 10-peak rwhp and 19 lb-ft over the previous numbers, but we saw gains of 24 lb-ft at 3,500 rpm.

Next, we installed the Performer RPM II in-house. The swap was relatively the same, and took us only a half a day to complete. We also had Ramsey write us another custom tune for an accurate comparison. Again, we strapped our Fox on the dyno and let it rip. This time our Fox made 310 peak rwhp and 330 lb-ft. We picked up 10 peak rwhp, lost 7 lb-ft, but the engine produced 28 horsepower more at 5,700 rpm.

In comparison, we picked up peak horsepower with the RPM II intake over the Performer, but lost a little torque down low. Due to the differences in runner length and size between the two intakes—the Performer, having longer and smaller runners, and the Performer RPM II having shorter and larger runners—this was expected. If you visit the track frequently, where you'll use the upper rpm range, then the RPM II may be better suited for you.

To finish our test, we installed a BBK Performance 70mm throttle body. Edelbrock recommends running a 70mm throttle body when running the RPM II intake. We strapped our Fox one last time to our dyno, and let it spin. Final numbers came in at 313 rwhp and 329 lb-ft.

1 We headed over to Ramsey’s Performance of Lutz, Florida, to handle the first phase of our install. Technician Ryan Frazier began by disconnecting the battery, vacuum lines, CAI, and draining the coolant. He then removed the upper intake.
2 Here, Frazier disconnected the injectors from the injector harness and set it off to the side.
3 He then disconnected the fuel lines and removed the lower intake.
4 With the engine valley exposed, Frazier then scraped off the old silicone and intake gaskets.
5 We then transferred the fuel rail and injectors from the old lower intake onto our new Performer. (Note: This is a good time to check the O-rings on the injectors to make sure they are not damaged.)
6a Frazier then applied silicone to the factory thermostat housing and installed it onto the new lower intake.
6b Next he installed new lower intake gaskets.
7 Here’s a comparison of the Cobra intake and our new Performer. Notice the difference in port design and size, as well as plenum size and runner length.
8 With everything prepped, Frazier then installed the lower intake.
9 He then installed the distributor and new upper intake gasket.
10 In order to install the upper intake, Frazier needed to grind down the PCV valve to clear our aluminum valve covers.
11 The new Performer intake looked right at home when installed. Frazier torqued the intake bolts to 18 lb-ft.