With new technology and new trucks come new problems to work around when trying to add more power. For example, take the new '07 Tahoes from GMC; some of these SUVs come with active fuel management to cut down on how much fuel these hefty trucks drink. The AFM system deactivates four of the eight cylinders while cruising, effectively cutting the fuel load in half. While this is great for saving money on gas, it does bad things to the exhaust note. What was a nice V-8 growl turns into something that sounds more like a clapped-out fishing boat. We are not going to sit here and tell you a four-cylinder can't sound good because they can, but this truck is only a four-cylinder during cruising. So, you get this muffled burble, instead of anything that sounds high-performance, which GM hides by keeping the exhaust very quiet.

So, what happens when you add a high-performance exhaust system to squeeze out more ponies? Well, if you buy substandard parts, you end up just amplifying that nasty burble. Luckily for all of you power-hungry truckers, JBA Exhaust Company builds a full exhaust system that not only adds 14.5 hp, but it also keeps that burble under control. Mark Matthews from JBA says, "This AFM feature was something we tuned our products for to avoid an unpleasant exhaust drone when in four-cylinder mode. Once installed, the new headers and exhaust system were tested extensively on the dyno and in real-world road conditions to ensure the operation of the AFM was not affected."

The Cat4ward headers and stainless steel exhaust system are available for '99-'07 Chevy and GMC 4.8-, 5.3-, and 6.0L V-8-equipped trucks and SUVs. The headers feature all of the good things you want to hear from a set of pipes, thick CNC laser-cut flanges, mandrel bends, and stainless steel. To top that off, you also get a limited lifetime warranty. The muffler and tailpipe assembly share some of the same features, such as mandrel bends and stainless construction, but also come with a straight-through-designed muffler and a 3-1/2-inch chrome-plated stainless tip with rolled lip. You might be asking why JBA chromed a stainless tip: Stainless has a tendency to turn yellow, and the chrome prevents that from happening.

To complement this system, JBA also offers a set of the company's PowerCables, which feature less resistance than the factory wires for more spark energy, and 8mm jackets for higher temperature resistance. Because these wires are made by the same company that makes the headers, they have all the proper ends to fit the new pipes. The parts are designed to be installed at home with minimal tools needed, so don't be afraid to tackle the job yourself. But, if you are not confident in your abilities, a professional shop shouldn't charge you too much to put them in.

Part One: The Teardown

Now that you know about the parts, let us give you some advice on tear-down and installation. JBA supplies great directions with its products, so the following information is just a highlight of some key points. You won't need a lift to do this job because the headers load from the top. But, you will be under the truck a lot, so a lift would be nice-a jack and jackstands will be sufficient. Before you grab a tool from the toolbox, grab some penetrating fluid like WD-40 and spray all the fasteners and hangers.

Side-By-Side
Once the stock system was removed from the Yukon, we laid it out next to the new JBA system. Here's how they matched up:

Part Two: The Install
Now for the installation of the new parts. As stated earlier in the story, both the left and right header feed in from the top. Be careful when you are sliding these into place, because one wrong move will break off a spark plug. You could remove them just to be safe, but as long as you are careful there is no need.

The Final Word
After everything was installed, the truck was strapped to a chassis dyno to see how much power the Yukon has now. As you can see by the numbers to the right, the installation of the JBA parts added 14.5 hp and 17 lb-ft to the peak numbers. Look at the numbers below 3,500 rpm; the JBA stuff really added some low-end grunt right in the sweet spot.

Read It And Weep!

RPM HP BEFORE HP AFTER TQ BEFORE TQ AFTER
2461 44.8 100.1 96 214
2552 56.2 117.0 116 241
2643 68.5 130.2 136 259
2734 79.2 139.6 152 268
2825 91.1 148.1 169 275
2916 104.2 154.8 188 279
3007 118.6 161.5 207 282
3099 132.8 167.4 225 284
3190 145.4 172.5 239 284
3281 156.5 178.3 251 285
3372 167.3 182.2 261 284
3463 175.6 186.1 266 282
3554 180.6 191.9 267 284
3645 186.7 198.5 269 286
3737 191.4 208.4 269 293
3828 196.2 219.1 269 301
3919 201.2 225.6 270 302
4010 209.6 232.9 275 305
4101 217.8 236.8 279 303
4192 229.1 241.6 287 303
4283 234.6 245.9 288 301
4374 238.5 250.1 286 300
4466 241.2 253.8 284 299
4557 246.9 256.3 285 295
4648 249.2 258.2 282 292
4739 248.6 261.3 276 290
4830 249.9 262.2 272 285
4921 251.6 265.3 269 283
5012 254.5 267.9 267 281
5104 249.2 268.2 256 276
5195 247.8 269.0 251 272
5286 243.9 267.2 242 266
5377 241.1 263.4 235 257
5468 239.5 263.1 230 253
5559 238.1 260.5 225 246
5650 237.2 256.1 220 238
5741 235.0 252.9 215 231
5833 233.7 254.1 210 229

SOURCE
JBA Performance Exhaust Co.
www.jbaheaders.com
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