Manifolds Vs. Headers - Exhaust Dyno Blast!

One area of engine science that shows positive returns is the exhaust system, particularly from the cylinder head to the muffler. It's been proven over and over again that headers add big power, so that's nothing new. Still, a lot of Mopar street enthusiasts are gun shy about bolting on a set of traditional tube headers. There's no denying the extra power, but moving to headers always has its potential pitfalls.

Though we don't hear people complain about the extra power headers produce, some guys would rather not put up with the usual header hassles. Tubular header pipes are never as quiet as a cast-iron stock exhaust manifold. Though the sound is sweet music to some, a lot of guys don't appreciate the tinny ring of traditional tubes-and nobody likes the ratty sound of a header leak. Many traditional headers for Mopar applications were drawn up decades ago, when the reason to bolt on a set of headers was to go racing-either on the street or track. The average street racer in those days couldn't care less about the headers' sound, learned to live with blown-out gaskets, and appreciated the featherlight weight of thin-flanged thin-tubed headers. In those days, replacing a set of rusted out headers every few years was just an expected part of the game.

Heavy Duty Headers: The Long And Short Of It
Hedman has been building their premium line of "Elite" street headers for years, initially developed for durability in truck and four-wheel-drive applications. Not many Power Wagon 4X4s found their way to the track, so in these applications the added durability and quieter running of a heavy-wall thick-flange line of headers were a natural. Hedman's Elite headers are made from heavy-wall 14-gauge tubing rather than the common 16- or 18-gauge, and the flange thickness was increased to an ultra beefy 3/8 inch instead of the typical 1/4 inch or 5/16 inch. The result is a quieter, more durable header, with flanges thick enough to hold a gasket without blowing out. The icing on the cake is a thermal coating that looks good and slows corrosion. Sounds like just the thing for a hassle-free street header on a Mopar musclecar.

Until recently, however, the Elite header line wasn't for older Mopar passenger cars, though Hedman as a company has built Mopar headers since the musclecar era. That's changed now with Hedman's introduction of the #78038 Elite series header for B- and E-Body big-block applications. The Hedman #78038 Elite header, like their most popular standard street header for Mopars, is a 1 3/4-inch tube four-into-one design, with a traditional 3-inch collector. We've thought for years that an Elite header for street musclecar applications would be the hot ticket and now they're here; but that's not all that's new from Hedman.

Other brands of cars have long had the option of short-tube headers, but for Mopar musclecar fans there just haven't been any around. We've even heard of small-block guys taking the short-tube Mopar Performance truck headers and modifying them to fit in early passenger-car chassis. Hedman filled this hole in the market with their new #78070 Shortie header for Mopar big-block B- and E-Body applications. Why go with a short tube? Tucked in tight to the block, the short tube collector doesn't hang under the floorpan, doing away with one of the biggest header hassles in a street application: ground clearance. Since the header collector is tucked up next to the block, ground clearance is simply not an issue.

With the short tubes, the header package becomes much more compact, making the header less intrusive in the engine bay. Service access for the plugs and various engine bay and chassis components can be awkward with four full-length tubes snaking down each side of the engine bay. Hedman went through a great deal of effort to make these new Shorties fit tight, and the final design has a nice symmetry not often found in short-tube headers. They found that the best design eliminated the bulky stock starter motor, so the new Hedman Shortie is designed to work with a mini-starter.

Dyno Duel
With exhaust options now running the gambit from stock iron manifolds to short tubes or full-length headers, the question becomes which one to use. We wanted to know how they stacked up in power production. Since we had a 440 on the dyno, it seemed like the perfect opportunity to wind them up and see for ourselves. Our test engine was a stout 440 street piece capable of 500 hp running fully ported heads (see "Stage V Booster Blast" in this issue). On an engine package built to this level, exhaust scavenging became critical, magnifying the effects of exhaust-system changes. For maximum output, this engine really wanted a set of 2-inch drag race headers such as Hedman's Husler #75340-but we were testing street headers, not full-house drag headers.

First, we bolted on a set of stock iron 440 Magnum manifolds. These had a nicely swept design, and except for the rare Max Wedge cast-iron headers, were about as good as it got in factory iron. On this high-powered 440, the iron manifolds were a blatant misapplication. We knew power would be way down, but some guys still insist that these old iron lumps work as well as headers. Winding up the 440 against the Superflow 901 dyno at Westech Performance Group, the 440 choked while exhaling through the open iron manifolds. The power numbers on this hot engine combo crashed, with the output listed in Tables 1 and 2, Columns 1. It was worse than even we imagined.

Next, we pulled Hedman's new Shortie design out of the box and bolted them on over the factory head studs. The Shortie hugged the block, making for a nice compact package. Though we didn't have the opportunity to bolt them on in a car, it looked as if the installation would be a drop-in. As the guys at Hedman pointed out, the Shortie header is designed to work with a mini starter, so the factory unit was replaced with a Summit #SUM-820337 mini starter. Weighing in at 10 pounds and generating 1.9 hp, the Summit starter was rated for engines up to 12.5:1 compression and 502 cid. At a reasonable cost of $160, the Summit starter was a nice upgrade, and fit well with the Hedman pipes. The Hedman Shortie comes with a 2 1/2-inch collector, and we made up some 2 1/2-inch exhaust extensions 18-inches long to route the hot gasses away from the works of the dyno. The Summit starter easily cranked over our big-block, and we wound the engine up with the Shorties. Power was up substantially over the iron exhaust, as shown in Tables 1 and 2, Columns 2. The Shortie was not up to the output of a full-length header, but made up a lot of ground, getting the output back up to a respectable level.

With the Shortie done, we stepped up to the Elite Series full-length header. The full-length tubes of the conventional four-into-one header have a distinct advantage over the other designs, if power production is the only criteria. Header manufacturers don't build headers with those four long tubes just for the fun of it. The longer tubes of a full-length header develop a negative pressure wave when an exhaust gas pulse exits the tube and enters the collector. This wave of negative pressure is reflected back up the pipe to the exhaust port, which scavenges the cylinder during overlap. For it to work, the tube has to be long enough for the pulse to reach the cylinder during the overlap phase within a usable rpm band. With a short tube, the tuned length is at such a high rpm, it doesn't come into play in the operating range of the engine. As expected, the full-length Elite Series header made the most power (Tables 1 and 2, Columns 3).

Conclusion
Though it was no surprise that the full-length header made the most power, there are other considerations in selecting the right exhaust for your application. Our 440 test engine, with its ported heads and longer-than-stock overlap, could take advantage of all the tuning that the full-length header could offer. With the reduced cam overlap in a near-stock 440, the differential between the various systems would undoubtedly narrow. Don't want the obtrusiveness of full-length header, but want to kick the power up with minimum hassle? The Shortie is the way to go. For all-out power with a solid heavy-duty street header, the full-length Elite is the obvious choice. The old iron manifolds have their place in a pure authentic resto, just figure out what you want from your system. With these new products from Hedman, now you can take your choice.