This test was our first time...
This test was our first time on Westech's second dyno, a 902 SuperFlow. It features a little swoopier styling and updated controls, but uses the same water brake, valves, and other major pieces. Westech reports this dyno reads within a couple of horsepower of the 901 SuperFlow we normally used. As it was, all of our intakes were within 3.7 lb-ft of torque, and between 4,000 and 5,000 rpm, so choosing one is difficult.
Horse Sense: The more we test the GT-40 intake manifold, the more impressed we are. It's well over 15 years old and it's still being compared to the most contemporary hot-rod intakes. Not many cams, cylinder heads, or other intake manifolds can say the same.
Steady readers know we've been giving our 347 dyno mule a serious workout by testing popular 5.0 intake manifolds. After running replacement-type intakes on both our 302 and 347 engines, this month we've stepped up to the street-strip intakes for those folks running small-blocks in the mid-400hp naturally aspirated zone.
While there are a surprising number of intakes available for the fuel-injected small-block Ford, we've confined our test to the usual gang of bolt-on-style suspects. That would be BBK's new Single Stage intake, Edelbrock's Performer RPM II, FRPP's venerable GT-40, the Holley SysteMAX II, and Trick Flow Track Heat. These are the appropriate intakes for a naturally aspirated test; the breadbox intakes and other specialty induction parts are better served by blowers/turbos, and should be tested on such engines.
Of our tested intakes, the BBK Single Stage intake is by far the newest design-so new in fact, that BBK said the unit we used was from the first batch built using production tooling. Apparently they were still fine-tuning the details on the fuel rails, but the castings are finalized, so the intake's performance is definitely representative of what's for sale.
Actually, final massaging of the BBK SSI plenum, runners, and so on since we ran it last has been minor and has had no effect on power production or driveability. The only meaningful changes are the fuel rails use a crossover tube that nests through the lower manifold's runners, and the adjustable fuel-pressure regulator sits about mid-manifold, again, under the upper casting. Thanks to the upper casting's open design, accessing the fuel regulator for adjustments is still easy.
What's new to say about the GT-40? It's been around almost as long as some of us (yes, there are those on staff who pre-date the staggered-round era...), and it remains a potent street manifold. It is difficult to beat the factory at its own game because it has so many resources to thoroughly develop such parts. Offered as a pure bolt-on, the GT-40 has carried the aftermarket's bull's-eye on its plenum since it was released in the late '80s, and it's still going strong, although it is hanging with tough company in this test. The one we tested is a pure stocker, and has pulled dyno duty at Westech, our normal dyno venue, for well over a decade.
Edelbrock's Performer RPM II supplanted its early Performer RPM intake a few years back. This has given Edelbrock a one-two punch in the 5.0 market, as the Performer does just fine on stock or minor bolt-on Mustangs, leaving the RPM II to handle everything from heavy bolt-ons to the ported heads, big cam, and long-tube-header crowd. It has proved to be an excellent unit right out of the box.
BBK's Single Stage intake...
BBK's Single Stage intake is obviously a different 5.0 H.O. intake manifold. Built using the usual upper and lower casting strategy, its twin-plenum design makes for a slightly more involved installation than the other manifolds in this test. The fuel-pressure regulator is easily accessed for adjustments, and the plenums clear the valve covers and provide good access to the injectors.
Holley's SysteMAX II is another high-achiever from a two-tier approach to the Mustang intake market. The SysteMax II has long been a good seller for Holley, and carries a well-known reputation for good power.
Similarly, Trick Flow's Track Heat is the higher-performance mate to its bolt-on Street Heat intake. The Track Heat is designed for the stronger bolt-on or better 5.0, and has a good power reputation.
If you haven't been keeping track, there seems to have been some rationalization in 5.0 manifold pricing. We've compiled typical mail-order prices for these intakes in the nearby sidebar, and all of them are within $50 of each other, with the exception of the Track Heat, which is an eyebrow-raising $100 less than its least expensive competitor.
For this test we wanted an engine with enough airflow potential to make these manifolds work a little while still being representative of what's actually running out there. We therefore selected our Coast High Performance 347 Street Fighter short-block and dressed it with a set of AFR 185 cylinder heads.
Ah, the good old GT-40. Designed...
Ah, the good old GT-40. Designed for a 245hp stock Mustang 5.0 engine, the GT-40 is out of its league in this test, but it still does a fantastic job of conserving torque while making enthusiast horsepower at real-world rpm levels. But once rpm exceeds 5,500, the GT-40 chokes, and porting won't do much for it.
We also reached for the largest camshaft in our test parts locker, a Comp Cams 282 Extreme Energy grind. To avoid the possibility of valve float, we replaced the existing, relatively light-duty valvesprings with a set of Comp 977 windings. They give a stout 160 pounds of pressure on the seat and 430 pounds open. This may seem excessive for a cam yielding 0.565/0.574-inch of valve lift and 232/240 degrees of duration at 0.050-inch of valve lift, but the dyno consistently shows a wiggly line around the power peak with these big hydraulic roller cams coupled with the typical springs fitted to assembled aftermarket heads. Fit a heavier spring, such as the Comp 977, and that wiggle goes away-so we're happy enough to err toward higher-rate springs.
As we have for the entire manifold test series, we ran FAST speed-density aftermarket engine management using 36-lb/hr FAST injectors. Since we're dangerous with anything more potent than a 7/16-inch combination wrench, we leave the computer tuning to Tom Habrbzyx at Westech. For this sort of testing, he locks the FAST system into a simple mode, allowing no adaptive changes to the fuel or spark. That means the computer tune is the same for all the intakes and, more importantly, it's not moving around on us during the test. That used to be a real issue when testing with EEC IV, but no longer poses a problem.