While every other commercial on TV advertises drugs that will treat depression, baldness, or that other male problem, none of them can match the therapeutic value of a healthy small-block Chevy running a set of long tube headers.
Unbeknownst to many SUV and truck owners, the 5.3L has a lopey idle that will present itself with just a little coaxing from a pair of headers and a catback. The factory exhaust note is unobtrusive and uninspiring. The Silverado SS's sounds better, but I wanted to wake up the K1500 a bit more while maintaining acceptable interior resonance and drive-by noise. Stainless Works has supplied catbacks for the Tom Henry Chevrolet Sport Trucks so I felt they could supply an OEM quality system, and I was not disappointed. With the addition of the catback the K1500's exhaust note changed from an apologetic sigh to a thunderous celebration of small-block power, and showed real power increases on the dyno.
Follow along as I continue to uncork the power potential of the 325-cubic-inch LM7 with Stainless Works headers and catback, and add a little insurance in the way of a Canton CM oil filter.
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The Stainless Works system upgrades the original single 2.5-inch outlet to a pair of 2.5-inch mandrel bent pipes terminating with polished 304 stainless tips. Although OEM exhausts have improved in construction and performance, they leave power untapped with restrictively quiet mufflers and crimped bends. |
To establish baseline power and dyno tuning I turned to John Sealock at Woodbridge Dynotech (540/753-1600).John took the time to let the truck cool down between runs and was patient enough to let me install a catback while the truck was still strapped to his dyno. For the baseline, catback and header sessions I had a full tank of 87 octane. |
The catback diverges from a 3-inch pipe and flange resulting in a system that looks and sounds like a true dual exhaust system. While some people will always prefer a rear exit dual exhaust system, I prefer the side exit for its installation simplicity and exhaust routing when towing an open trailer. |
The Stainless Works tips are highly polished, double walled, 304 stainless steel. While understated, they offer a significant visual upgrade that doesn't scream for attention like the six-inch fart pipes that the import crowd is so fond of. |
Disconnecting the right rear lower shock mount and jacking the body to increase the space between the rear axle and body simplifies catback removal and installation; I was able to make the swap in less than two hours with the truck strapped to the dyno. |
After years of poorly designed and constructed exhaust systems the factory pipes are now quite good, but Stainless Works still found room for improvement using 304 corrosion free stainless and mandrel bends. The dual mufflers look and sound reminiscent of the chambered exhaust of the first generation F-bodies. The factory muffler looks like a garbage can compared to the Stainless Works units. |
The spark plugs, wires and dipstick should all be removed to facilitate the header swap. The Y-pipe nuts can be difficult to loosen so break the nuts loose before unbolting the manifolds. Due to the LS-series' exhaust port spacing, fasteners and spark plugs are easy to get to. |
The hardest part of the header install is the Y-pipe removal. I found it easiest to unscrew the driver's side O2s, as their harness connections are hard to get to and to just unplug the passenger side harness. A plastic bag protects the O2s from contamination. A floor jack supports the transfer case so I can drop the trans X-member. |
Comparing the stock iron exhaust manifold against the SW header illustrates the differences between mass production and hand built fabrication. Modern iron manifolds are works of art compared to the boat anchors of the past; therefore it takes a pair of long tube headers to see significant improvements over modern iron manifolds. |
The Chevrolet Service Manual recommends using GM P/N 12345493 threadlock, new fasteners and new gaskets when reinstalling manifolds. I reused the gaskets and fasteners and have not had an exhaust leak. Stainless Works flanges are the same thickness as the cast-iron manifolds, so bolt length is not a problem. |
Stainless Works uses a four into one merge collector that adapts down to a 2.5-inch slip fit connection. The beautiful TIG welds found on the headers have a rainbow-like color and are no larger than twice the material thickness, indicative of a high quality weld.As I am planning a wideband dyno tuning session, Stainless Works installed an extra O2 bung at my request. |
Stainless Works designed its Y-pipe to include a pair of Random Technology cats in the stock location while allowing room to install a full-length header. While not 50 state legal, the headers retain all emissions components in the stock locations that should please all but the stingiest inspector. |
As per SW's direction, the passenger side header went in from the top. Thanks to the trucks' cavernous underhood area and the compact LM7, header installation does not require a blood sacrifice. The driver side header installs from underneath without difficulty. |
OBD-II engines are extremely sensitive to the slightest exhaust leaks. Stainless Works has found a light coating of O2 sensor safe high temp RTV prevents exhaust leaks and makes it easier to disassemble exhaust components if needed. |
Stout 0.375-inch flanges secure the Y-pipe-to-cat-back connection. On mine, as well as other '04 trucks, the Y-pipe studs are too short, so I pounded them out with a five-pound sledge and replaced them with bolts. A graphite donut gasket replaces the OEM metal-to-metal connection and has been leak free since installation. |
The driver side headers clear the steering shaft and frame rail without trouble. |
In addition to the performance mods, a Canton CM replaceable element filter (P/N 25-232) will help the LM7 survive the abuse I intend to give it. The CM's synthetic filter element works down to 8 microns and is so efficient that it does not use a bypass, allowing 100 percent filtration even during cold starts. The replaceable element is good for about 12,000 miles on the street and 750 miles of racing use. While Canton offers an external mount version for even longer life, I opted for the convenience of the spin-on. Since the element is removable, it is easy to see what is going on inside your engine. This is a great example of race car technology trickling down to the street. |
The supplied Accuseal clamps should be oriented for easy access to the fasteners and so they don't rattle against any frame members. After the test drive the stainless tubing took on a gold color; what is not evident in this picture is the O2 sensor I forgot to hook back up resulting in a check engine code. Due to stainless steel's high rate of thermal expansion, the Accuseal clamps should be checked for tightness after a test drive. |
After removing the factory imposed 94mph speed limit and setting the transfer case to 2wd, the baseline dyno run resulted in 244.1 rwhp and 276.3 lb-ft of torque. After the cat-back installation, back-to-back runs resulted in 251.8 rwhp and 283.1 lb-ft of torque, a gain of 7.7 hp and 6.8 lb-ft of torque. (Note that dyno spikes resulted in slightly different horsepower numbers and exaggerated torque readings.) Considering the computer had no time to relearn and the increase was noted across the rpm rage, this is a real gain. The headers were good for another 9.8 HP and 10.3 lb-ft of torque. Due to circumstances beyond our control, a different Dynojet had to be used for the header numbers, but that dyno was set up identically to the previous unit. |
After the header install I logged several 0-60 runs with HPTuners' VCM software. After five runs with all wheel drive enabled I was able to record a best of 6.419 seconds. While this is a respectable number for a 4400-pound truck with a 325-cubic-inch V-8, I suspect the stock tune and airbox is holding back the performance potential of this combination. |