Steve Baur
Former Editor, Modified Mustangs & Fords
August 1, 2008
HP Performance's Sean Story handled the task of swapping manifolds so we could snap pictures. Normally the intake swap is a piece of cake, and for the most part, ours was, too. However, if you run a lot of aftermarket parts, you'll want to check for fitment issues that may pop up. The RPM II intake actually fit better than our previous intake manifold.

Anderson also noted that we should step up to an 80 or 85mm throttle body at this time, and to accomplish this we called Accufab for one of its shiny polished pieces. We also specified an EGR blank spacer, which positions the throttle body in its correct location so that the AFM Power Pipe and throttle linkage all line up. The throttle body and spacer kit (PN F80K) retails for $320.

For the installation, we went to HP Performance in Orange Park, Florida, as Stolen Goods had numerous baseline dyno pulls from which to compare the new intake manifold. Switching manifolds is usually a fairly simple deal with a stock Mustang, but when you have as many aftermarket parts as Stolen Goods does, you have to expect a surprise or two with fitment. Our two main concerns with this were the strut tower brace and the water-neck to water-pump clearance.

As it turns out, we actually gained clearance with the Edelbrock unit, and we also picked up a little clearance between our throttle cable bracket and the Ford Racing Performance Parts valve cover. (Astute readers will remember that we had to modify the bracket so it would fit with the valve covers. The bottom of the upper plenum, where the runners curl over top of the driver-side valve cover, was a tight fit, and we weren't able to use the vacuum fittings from the Trick Flow manifold. This was easily remedied as the RPM II upper plenum offers vacuum ports at the back corner facing the firewall.)

After draining the coolant from the engine, remove the upper plenum along with all of the linkage and vacuum lines. The fuel lines are next, as is the fuel-injector wiring harness.

Of course, what you really want to know is how it performed. After hooking up our '93 Cobra to HP's Dynojet dynamometer, our first hit was a little on the lean side, with the air/fuel ratio reaching 14:1. Still, power increased to 371.59 and torque fell to 371.75 lb-ft. HP Performance's Tony Gonyon had used an SCT chip to tune Project Stolen Goods before, so tuning changes were only a keystroke away. After checking the data from the SnEEC datalogger that he uses for all of his Fox-body tuning, Gonyon added about 5 percent more fuel, and the subsequent dyno pull netted 372.04 hp and 383.60 lb-ft of torque at the wheels. Air/fuel was steady at 13.3:1, and both power and torque increased across the entire rpm range.

Gonyon noted that the engine seemed to rev smoother and throttle response was improved. We concurred after a quick drive around the block and were pleasantly surprised with the side effect of the manifold swap. With the added horsepower and torque, traction is definitely an issue on the street, even with the sticky Falken RT-615s currently on the car. We may have to look to using a drag radial for everyday driving, but that's a good problem to have.

Next month, we'll swap out the 3.55:1 ring-and-pinion gear set for a stout 4.30:1 setup in our quest for an 11-second timeslip. We'll also swap out the Torsen T-2R differential for a Traction-Lok from FRPP, as Torsen doesn't recommend clutch drops with the T-2R. Between now and then, we'll see if we can't get back to the track with the 3.55s and see what the snake can do.