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5.0 Mustang Street/Strip Intake Manifold Test - Close Call
Dyno Testing The Current Crop Of 5.0 Street/Strip Intake Manifolds On A 347 Uncovers A Tightly Knit Group
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.
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.
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.
The issue with FAST is the same finicky demands for the right aftermarket hardware other aftermarket engine-management systems have shown. We pulled our hair out trying to get the engine to stop missing at 4,700 rpm until we changed from our original MSD magnetic pickup distributor to a TFI-style MSD distributor. FAST and the window spacing on the original MSD don't get along (neither did the AEM system we sampled a while ago), but the TFI/FAST combination ran great. Aftermarket engine-management systems all seem to accept the stock ignition system, too, including the distributor.
We ran our usual electric water pump and 1 3/4-inch Hooker headers. The electric water pump frees up a bit of horsepower; the generously sized long-tube headers help build it. Comparing one dyno test to another is nearly impossible due to, among other things, variances in dynos, so we caution you to subtract 10 or more horsepower from our figures compared to an engine with full front engine dress.
As it was, our engine made 420 to 450 hp depending on the intake, so it was no wallflower. In the real world, we estimate our test mule would generate 360 rwhp when installed in a Mustang, running a full front-engine dress, breathing through streetable mufflers, and so on. Healthy enough, in other words.
And a final dyno disclosure-we ran this test on Westech's engine dyno number two. Heretofore all our testing has been on dyno one, which is a 901 SuperFlow. Dyno two is a 902, so it looks a little swoopier in the photos. Westech says the two dynos read within 2 hp of each other; since they dyno on them every day, we'll take their word on that.
It doesn't take much eyeballing of the results to note the BBK and GT-40 intakes make up one performance group, while the Edelbrock, Holley, and Trick Flow form another higher-output group. This makes sense because the GT-40 is an older design that dates from the days of simple bolt-on Mustangs and originally designed for the warmed-up version of the 5.0 H.O. engine eventually released in the '93 Mustang Cobra. The SSI is BBK's entry-level intake designed to run as well as possible on light-duty bolt-on cars but not necessarily placate the more aggressive strip warriors. Aimed at the same end of the market, it's no surprise they run similarly.
On the other hand, the RPM II, SysteMAX II, and Track Heat are all marketed to the harder-core street-strip market. And these three musketeers make amazingly similar power. This is especially true of the Holley and Trick Flow intakes, which are never 4 hp apart, and indeed, measured within 1 hp of each other over 80 percent of the time. The Edelbrock is similar, but does trade in a few lb-ft of torque in the midrange for that much stronger a top-end.
To be more specific, the RPM II and the SysteMAX II/Track Heat pair make within 2 hp of each other as they climb to their power peaks, but the RPM II keeps making a little more power all the way to our 6,000-rpm test limit, whereas the other two begin falling off. This gains the RPM II 3 more horsepower over the Holley and Trick Flow.
In fact, the Performer RPM II was this test's top dog-the only intake to sneak past the 450hp barrier. It posted the highest peak power, both in rpm and horsepower, and it hangs on to its power-making potential longer than the other intakes. Some of these trends are not huge, but they are pronounced enough to label the RPM II as the most horsepower-friendly intake here.
Thinking about the BBK and GT-40? Don't think they aren't worth considering because they were 25 or 30 hp behind the high-achieving Edelbrock/Holley/Trick Flow tripartite in peak power. While their lower-rpm torque advantage is not enough to offset their top-end horsepower deficit in this crowd, up to 4,500 rpm they are ahead of the top-end specialists. If your combination doesn't often see more rpm than that, the BBK or GT-40 will drive better and go a few feet farther with a gallon of gasoline. Of course, that describes a daily driver; if yours sees only the odd track day, the BBK and GT-40 are worth considering. Of course, if revving action is what you're after, the top-end manifolds are your best choice.
Comparing the BBK and GT-40 is something of a mixed bag, as the twin-plenum BBK has several peaks and valleys, but finishes stronger than the GT-40 with an extra 5 hp and a better ability to hang in there at high rpm. The GT-40 responds with a strong midrange and by far the lowest peak horsepower rpm. That means it delivers its power a bit stronger and earlier, which is useful on the street or in heavier cars. On the other hand, the GT-40 positively dies at higher rpm. It is the only manifold in this test that truly dives at the top of the tach, so it's not a good choice for an engine that will see 5,500 rpm or more on a regular basis.
As always, the combination of engine, gearing, car weight, intended use and a hundred other factors will help you make your intake choice. But when it comes to easily purchased and installed 5.0 intakes, the street/strip market has an intake for every need.
Here is a sampling of mail-order prices for the manifolds in our test. We gathered these prices from ads in this magazine, and retail prices will vary. The BBK intake includes fuel rails, which are required to fit its intake. They are higher volume than stock, so they are a good bargain.
All of these intakes include top-to-bottom gaskets, hardware, and installation manuals. The Edelbrock, FRPP, Holley, and Trick Flow intakes are conventional designs and have no "hidden" bolts under or inside the top casting, so they are easy to install. The BBK is also easy to install, but is a bit specialized, so it features more bolts, stand-offs for the fuel rails, and it requires mounting the fuel regulator.
|BBK SSI||$549.99 ($699.99 w/70mm TB)|
|Edelbrock Performer RPM II||$599.95|
|Holley SysteMAX II||$569.88|
|Trick Flow Track Heat||$450.00|
Performer RPM II
|RPM||Holley SysteMAX II||Trick Flow Track Heat|