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

Hot-rodders are never ones to leave well enough alone, and the Muscle Mustangs & Fast Fords staff members are certainly guilty of that. After we completed Project Stolen Goods, our resident '93 Cobra, we wondered about the many what-ifs that we hadn't tried. This month, our what-if revolved around two main premises that involved two key players in the Stolen Goods buildup.

D.S.S. Racing's Tom Naegele felt that our big-bore (4.125 bore/ 3.25 stroke) 347 Boss engine should be making more than our current 400 (estimated) flywheel horsepower it had produced thus far. The components we chose for our induction setup were a little too mild to offer that level of peak power, but it did produce an abundance of torque, which is what we were aiming for. We had queried Anderson Ford Motorsport's Rick Anderson about which intake cam and heads to use, and he specified AFM-ported Trick Flow Twisted Wedge cylinder heads, an AFM B-41HR camshaft, and a Trick Flow Track Heat intake manifold.

Anderson's recipe delivered exactly what we wanted: a torque-oriented motor that would take advantage of a 3.27-3.55 rear gear ratio. Moreover, it would be perfect for real-world driving and/or coming off a corner or a stoplight. When asked about Naegele's expectation, Anderson noted that a different intake manifold should pick up another 20 hp, but in trade it would lose about 30 lb-ft of torque, and after all, we did build it for torque.

The Performer RPM manifold was redesigned a few years back, and the new RPM II can be had in a mean-looking black powdercoat (PN 71233). The manifold comes with everything you need short of intake gaskets and a tube of silicone.

With 358 rwhp and 376 lb-ft of torque, we were pretty satisfied with the way the engine build turned out. The torque makes the car loads of fun to drive whether on the street or at the track. We suppose it's those pesky LS1-powered ponycars that drove us to the intake-manifold test. We've seen bolt-on 346ci LS1s make the same amount of power as Stolen Goods, but their torque peak was much higher in the rpm band. That's not always a bad thing, though, as too much torque can make it difficult to get traction in low-speed situations.

During a recent editorial meeting, Editor Evan Smith made it known that he wanted our teal project car to nab an 11-second timeslip at the strip, and those questions regarding power output were enough to convince us a few tests were in order.

It wouldn't only be a question of power and torque with the different intake manifold, but also one of driveability and the fun factor on the average street cruise. Would we lose torque in trade for power? Would it hurt us at the strip? Would it make the car a dog to drive on the street? These are all questions we hoped to answer, and some of them were solved in the first part of the story. This month, we'll cover the intake-manifold install and dyno test. Next month, we'll throw a steeper gear at the Cobra and let it all hang out. We're tempted to run it again with the 3.55s and the new intake, so we'll see if we can squeeze that in.

Accufab has a throttle body for every application. For our test, we chose this 80mm unit with a blank EGR spacer.

Your author had been considering the Trick Flow R manifold, but apples to apples, the Trick Flow Track Heat we were already using was comparable to the Edelbrock Performer RPM II intake suggested by Rick Anderson. The R manifold is said to work best between 2,500 and 7,250 rpm, whereas the Track Heat and RPM II are both suited for 1,500-6,500 rpm. With our 347 making peak power at 5,800 or so, it seemed the Edel-brock piece was the way to go if there was any power left on the table. Anderson agreed and noted that the Trick Flow R seemed to work best on larger 393-408ci motors.

After that assessment--and seeing that Edelbrock was offering a black powdercoated finish that would match our engine-bay theme--we ordered an Edelbrock Performer RPM II intake manifold (PN 71233). It retails for around $820, with the silver finish being a little cheaper and the polished version requiring a bit more bacon.

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.

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