Tom Wilson
May 1, 2004

Horse Sense:
Previous tests have shown unequal-length short-tube headers are worth around 7 hp on a near-stock 5.0 engine, while equal-length short-tubes typically pick up around 11 hp. Frankly, we were amazed at how similar the power output was with the four BBK headers

For years, debates have raged over what exhaust system is best for late-model Mustangs. Short-tubes or long-tubes, H-pipe or X-pipe, cats or off-road-every piece has it adherents and proselytizers. Without a doubt, this topic is as hot as Fireball Urist's primary pipes.

While we had our 347 dyno mule up on the pump at Westech recently, we double-timed through several sets of headers for a quick revisit of the Mustang header debate. Our goal was to run both equal- and unequal-length short-tube headers to see if the hassles of the equal-length units were worth it. And then we moved to long-tube headers to see if 1 5/8- or 1 3/4-inch primary tube diameters made any difference-not a big test, but a quick look at the two major choices in Mustang headers.

As we were testing on an engine dyno, fitting pipes downstream of the headers was an issue. This almost always is true, as engine dynos have a supporting structure that differs greatly from undercar real estate. In this case, it meant running a set of 2 1/2-inch pipes, without mufflers. In reality, these pipes were BBK's off-road H-pipe for short-tube headers, but run without the interconnecting short H-section. We did not connect the H-section because, for starters, the headers would not fit on the dyno that way, and second, we wanted to run both the short-tube and long-tube headers with the same "exhaust pipe," and there was no way they were going to "H" when bolted to the long-tubes. Furthermore, because these pipes had the ball-joint flange as used by Ford and BBK, they were quickly bolted-up to all the BBK headers, albeit at angles reminiscent of a downhill skier going into the fence at 60 mph.

BBK was kind enough to supply us with the following headers and H-pipe for our test.

BBKTube
PNDiameterDescription
1515 1 5/8 in'86-'93 unequal-
length shorttube, chrome
15121 5/8 in'86-'93 equal-
length short tube, chrome
15161 5/8 in'79-'93 full-
length headers, chrome
15941 3/4 in'79-'93 full-
length headers, chrome
15072 1/2 in'86-'93 off-road
H-pipe

Photo Gallery

View Photo Gallery

These are popular part numbers, especially the short-tube versions. You may notice in the photos that some headers were indeed chromed, while others were not. This is only because BBK pulled some of the headers out of its warehouse, while others were grabbed after welding but before chroming. It makes no difference in power production, and it saved BBK from having to open some product that was on the shelf and ready to go.

The Test Engine
We tested the headers on our usual engine-dyno mule, a Coast High Performance 347 Street Fighter short-block fitted with Ford Racing Performance Parts Z304 cylinder heads, a stout Comp Cams hydraulic roller, and an Edelbrock Performer RPM II intake manifold, all controlled via an AEM Plug and Play engine-management computer (we'd been fiddling with the AEM computer, but that's another story).

During the earlier computer testing, we had also been running the standard Westech dyno exhaust, a set of Hooker Super Competition 1 7/8-inch primary and 3-inch collector long-tubes, about 4 feet of 3-inch exhaust tubing, and a pair of 3-inch inlet and outlet Flowmaster mufflers. We've tested with this system many times, and we know from repeated trials that removing the pipes and mufflers makes no difference in torque or horsepower. This engine combination produces 400- to 450 hp, depending on tuning and ancillary parts.

The Results
Frankly, we were amazed at how similar the power output was with the four BBK headers. The expected trends were there, but not as exag-gerated as we had thought going into the test. The long-tubes made more torque than either of the short-tubes, but there was little to choose between the two long-tubes.

Well, the 1 5/8-inch long-tubes were nearly 10 lb-ft to the good compared to their 1 3/4-inch brothers down around 3,000 rpm, but this was evened up by 3,600 rpm. At the top end the larger-diameter long-tubes held a slim 2-4hp advantage right around the power peak. Otherwise, the long-tubes may as well have been identical runs.

So, while the difference between the long-tubes was small, the expected higher torque from the smaller pri-mary pipes was evident, as was the higher power from the larger-diameter primaries.

As for the short-tubes, the meaningful story was once again torque. Up to almost 4,000 rpm, the equal-length short-tubes held a distinct advantage, out-torquing their unequal-length brothers by 7 lb-ft or so. Across the midrange the power contest was too close to call, then, strangely enough, the unequal-lengths pulled ahead by approximately 5 hp at the top end.

Could it be the longer primary length of the equal-length short-tubes enhances torque, but at higher rpm the twists and turns of the tightly wound equal-length pipes is more restrictive than helpful?

And then we could not help but notice the Hooker headers and mufflers were up to 25 hp ahead of anything in our BBK test suite. While we were not planning on comparing these headers with those in our test line-up, we had, indeed, run them under identical conditions the same day.

So why were these dyno headers so much more eager? We don't know for sure, but we have a couple of thoughts. For starters, the Hookers have larger primaries at 1 7/8 inches diameter, with the occasional slip joint to facilitate installation. This also means straighter runs with fewer kinked bends than the fully welded BBKs. Second, the Hooker Super Competition design uses a traditional, flat, three-bolt flange designed to seal with a gasket at the exhaust pipe end. This has two interlocked power benefits-a longer collector and no Ford-style ball-joint connection.

The longer collector provides what looks to be a much easier merge from the primary pipes into a 3-inch collector. That gradual merge and unrestricted 3-inch collector diameter certainly look as if they pose no restriction, and may allow more scavenging effect.

Looking at it the other way, the Ford-style ball-joint flange forces a truncated collector, plus the ball-joint flange curls inward, well into the exhaust gas path. In other words, just looking at them, the ball joints appear restrictive, and our dyno data would certainly indicate that. Unfortunately, we didn't have a pile of identical headers with different collectors and flanges on them to sort all this out. The good news is we now have another dyno test idea up our sleeve.

Of course, much of this is aca-demic on the street. The ball-joint flanges are what Ford uses, and thus most aftermarket systems are designed to mate with them. The ball joint is also forgiving of misalignments and seals tightly the first time. It has no gasket to burn out, the hardware is good and large, it accepts high-tightening torque, and it doesn't occasionally loosen-all issues with traditional three-bolt flanges.

What we can say is, despite the possibilities of burned ignition wires, equal-length short-tube headers would seem worth the cost and hassle on moderate-power street machines. And if you're going for long-tube headers on a race car, then going all the way with big tubing is the power-savvy choice.

On the Dyno

Unequal-LengthEqual-Length1 5/8-in1 3/4-in
1 5/8-in Short-Tube1 5/8-in Short-TubeLong-TubeLong-Tube
RPMTRQPWRTRQPWRTRQPWRTRQPWR
3,000346198354202384220376215
3,100344203353209382226376222
3,200346211359219389238378231
3,300365230372234392247389245
3,400375243382247393254391254
3,500380253387258393262392262
3,600385264393270395271396271
3,700390275396279395279397280
3,800395286403292400290402291
3,900406302408303405301407303
4,000413315414316411313412314
4,100417326419327416325417326
4,200417334419335416333417334
4,300416341416341416341416341
4,400414348415348413347414348
4,500414355413354410352412353
4,600414363412362410359412362
4,700414371414371410367413370
4,800416381414379410376415379
4,900418390414387412384416389
5,000418398413393411392417397
5,100413402410398407396413401
5,200409406405402404400407403
5,300404408399403398402403407
5,400398410394406392404396408
5,500382401383401385404387406
5,600377402374400378403374399