Wes Duenkel
October 6, 2010

Choosing the right size headers is important to maximize power, especially when using nitrous. Primary tubes that are too large may prevent the engine from hitting the "sweet spot," and primaries that are too small choke the engine and restrict output.

How much? Don Jackson of Lebanon, Tennessee, wanted to find out. His '79 Mustang Cobra has been raising eyebrows at the region's eighth-mile tracks for some time. It looks harmless-it doesn't have a cowl hood, pizza-cutter front tires, or a gutted interior. Only the drag radials hint at the car's potential. But his nitrous-fed 393ci stroker powers the Cobra to consistent 6.40s in the eighth and embarrassing the competition on a regular basis. The only missing piece was a properly sized exhaust to let his big-inch Windsor breathe.

Nitrous-injected engines require generous exhaust flow. An exhaust system that is properly sized and tuned for a naturally aspirated engine can be on the small side when a lot of nitrous is used.

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But even by naturally aspirated standards, this Mustang's exhaust seemed woefully inadequate. A leftover from its milder days, the '79 exhaled through 1 5/8-inch shorty headers, a 2 1/2-inch off-road X-pipe, and a 2 1/2-inch after-cat. With 393 ci and a 180hp-shot of nitrous, this Fox was long overdue due for better pipes.

With arguably the widest selection of tubing sizes, lengths, and engine applications, Hooker headers was an obvious choice. Jackson's engine builder, Darryl White of Revolutionary Performance and Machine, recommended Hooker PN 6228-1 headers. They feature 2-inch-diameter, 30-inch-long primary tubes; 3 1/2-inch collectors; and Hooker's metallic ceramic thermal barrier coating. FlowTech's 3-inch cross-pipe kit and a few reducers would connect the Hookers to a 2 1/2-inch MAC after-cat since Jackson races his car in full street trim.

The specialists at C&C Performance in Carthage, Tennessee, were eager to help with the installation and dyno work. The husband and wife team of Casey and Capri Lawson run this "little shop that could." Besides Jackson, they have many customer cars that regularly punch above their weight. A visit will usually find Casey under a car on the lift and Capri running the dyno. With several eighth-mile tracks within an hour or two of their shop, their Dynojet 244XC doesn't get much rest-and Capri is just as likely to get dirt under her nails as Casey.

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First, Jackson's Cobra was strapped down for a couple baseline runs. Naturally aspirated, the stroked Windsor made 346 hp and 344 lb-ft to the wheels. Output jumped to 482 hp and 522 lb-ft on nitrous.

The car had barely cooled before it was open season on the exhaust. With the '79 on the lift, the headers and X-pipe were stripped from the Mustang. Hooker's 2-inch by 30-inch primaries and 3.5-inch collectors certainly dwarfed those of the shorty headers, but how much power would they unlock?

To fit the cavernous 2-inch primaries to cylinder heads with a standard exhaust bolt pattern, such as the World Products Windsor Senior heads on our test subject, the Hookers come with adapter plates. For maximum performance, the ports on the plates should be enlarged to match the heads. A few minutes with a die grinder opened up the holes sufficiently.

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The extra clearance offered by the car's QA1 tubular K-member and the Hooker's multi-piece design kept cussing to a minimum while jockeying the headers into position. Only the starter had to come loose for a bit more working room. Once the headers were bolted up, the crew started measuring, cutting, and fitting the Flowtech universal cross-pipe kit. A set of slip-fit Hooker reducers mated the 3.5-inch collectors to the cross-pipe's 3-inch tubing, with another pair of reducers and ball-and-socket adapters completing the 2.5-inch after-cat connection.

With all the joints welded and clamped, it was back to the dyno. Naturally aspirated, Jackson's stroked Windsor made 356 hp and 342 lb-ft of torque. The 10hp gain was encouraging. With such large-diameter primary tubing, the crew expected a slight loss of torque and horsepower off the bottle. Would a modest power increase with a marginal loss in torque on motor alone mean bigger gains with nitrous?

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It did. With the bottle warmed up, Jackson made his nitrous pull. The result was 517 hp and 549 lb-ft to the wheels-a solid 35hp and 27-lb-ft gain! Without any tuning changes, the air-fuel ratio was in the high 12s and low 13s, so for consistency, the crew left everything alone. It's worth noting that the converter allowed the engine to flash to its peak torque at the start of each pull. That, combined with a typical torque spike at nitrous engagement skewed the peak torque numbers a bit, but the horsepower figures are nonetheless impressive. Figuring a 25-percent driveline loss through Jackson's C4 transmission, the headers were good for 44 hp. Needless to say, Jackson and the C&C Performance crew were very pleased.

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In true MM&FF fashion, we wanted to see what the newly found horsepower would equal at the track. Jackson's previous best eighth-mile pass of 6.41 at 105 mph was made in cool, dry February air on a perfectly prepped track, so beating it would be a tall order. Uncooperative springtime weather and lackluster traction scrapped several attempts. In late spring, Jackson clipped off a clean pass, albeit in air that was 87 degrees and an equal percentage of humidity. The best Jackson could muster was a 6.53 at 105 mph. Clearly, the initial track times were not as conclusive as the dyno results. But the fact that Jackson's '79 ran the same mph in poor air has Jackson confident that quicker time slips are in his future. Besides, who would be disappointed about unlocking 35 rwhp with just an exhaust change.

Naturally AspiratedNaturally Aspirated
Before HeadersAfter HeadersDifference
RPMHPTQA/FRPMHPTQA/FHPTQNotes
4,00024932711.24,00025633611.379
4,10025632911.94,10026533911.9810
4,20026633212.34,20026933712.434
4,30027333412.44,30027433512.611
4,40028634212.54,40028333712.7-4-4
4,50029434312.64,50029033912.6-4-5
4,60030134412.64,60029934212.6-2-2
4,70030834412.64,70030534112.6-3-3
4,80031434312.74,80031434312.700
4,90032134412.84,90032034312.8-2-2
5,00032734412.85,00032734312.8-1-1
5,10033034012.95,10033234212.833
5,20033433712.95,20033834112.944
5,30033833513.05,30034334013.154
5,40034133213.15,40034533513.144
5,50034432913.15,50034933313.244
5,60034632513.15,60035132913.244
5,70034431713.15,70035332513.398
5,80034331113.05,80035632213.21211Largest HP and TQ peak gain
5,90034430613.25,90035531613.4109
6,00034229913.26,00035130713.598
6,10033829113.26,10034529713.576

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NitrousNitrous
Before HeadersAfter HeadersDifference
RPMHPTQA/FRPMHPTQA/FHPTQNotes
4,70046752213.24,700N/AN/AN/AN/AN/A
4,80046651013.14,800N/AN/AN/AN/AN/A
4,90046850212.74,90051254914.04548Nitrous torque spike?
5,00046949312.65,00050452913.53537Nitrous torque spike?
5,10047048412.55,10050451913.13435
5,20047347812.35,20050450912.93031
5,30047847312.25,30051150712.83433
5,40048046712.15,40051249712.63231
5,50047845612.15,50051349012.43534
5,60048045112.15,60051548312.43432
5,70048244412.25,70051547512.43331
5,80047943412.25,80051746812.33734
5,90047942612.35,90051445812.23531
6,00047741812.36,00051344912.23631
6,10047040512.36,10051144012.24135Largest HP and TQ peak gain
6,20046839712.36,20050743012.23933

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