Custom Exhaust System Build - You Tube

You don't have to bend or notch to make a custom exhaust. Even better, "kinky" tubing bends are now easily avoidable. Skilled 4x4 owners who can cut, grind, and weld can build a custom system from ready-made components. (Think Tin Man from The Wizard of Oz.)

The 4x4 Aftermarket Offers "bolt-on"-or at least "less hassle than making your own from scratch" solutions to many popular conversion dilemmas. But the further away from stock the vehicle gets, the higher the likelihood that no off-the-rack kits exist for connecting certain dots in their new locations.

Exhaust is one such area. Changing the powertrain and scrapping the OE suspension for something longer-travel often adds up to a total reroute of the exhaust system. Good exhaust shops are worth their weight in gold-and often charge accordingly. However, the average exhaust center isn't off-road literate and will likely choose the route of least resistance instead of factoring in suspension travel, ground clearance, and other parameters that don't apply to commuter cars.

The good news: 4x4 owners who have the skills to get themselves into conversion predicaments can often make their own custom exhaust systems. Readily available tubing and bends make the job possible without the need to invest in a notcher and bender. Brian Wallach of American Offroad shared a few pro tips that can help home-garage warriors achieve custom-exhaust success.

Materials

Tubing: Cut-and-paste (i.e., weld or clamp together) exhaust kits are available from some of the companies listed in the Sources Box. (Most common are stainless steel kits marketed for street rods.) Another option is to buy lengths of tubing and an assortment of premade mandrel bends. In larger cities, these parts are available from undercar suppliers; some mail-order sources are listed below.

Straight lengths of tubing and ready-made mandrel bends in a variety of configurations make it possible to fabricate a high-performance exhaust system without a bender or notcher. DIY exhaust kits often include swedged ends for easy slip-fits.

Even engine-swap headers such as this YJ/Vortec V-8 set from Advance Adapters sometimes need tweaking to clear nonstock chassis components. The collector dump is shortened to increase clearance at the motor mounts and Black Diamond link arms.

The modified headers are reinstalled. This second test-fitting is necessary for downpipe routing.

The first decision is whether to use stainless or aluminized steel. The main differences are cost and durability. Stainless steel will theoretically last the life of the vehicle, but it's more expensive than aluminized tubing and harder to weld (requiring either the right wire for MIG welding or time-consuming TIG welding for highest-quality results). Wallach recommends seamless 304-grade stainless as the only real option for vehicles in coastal salt-air areas. A less-expensive stainless grade is 604, an alloy that falls between 304 stainless and aluminized tubing. If choosing cost-effective aluminized tubing, be aware that its seam is the most common rot point. Position the seam at the top whenever possible to minimize the amount of condensation that accumulates on it.

Tubing diameter is the next consideration. Bigger is often better, but too big can actually strangle power-air has mass that must be moved through the tubes. Excessive backpressure can result when ambient air significantly slows down exhaust velocity.

Magnaflow publishes general exhaust-diameter guidelines based on engine size and power (for systems with single in/out mufflers):

The collector flange is placed on the header. Then it's snugged to the downpipe flange and aimed for proper clearances. Next, the collector flange is tacked to the header, then the assembly is removed and final-welded around the exterior.

Trial-and-error is the path to optimal routing. A cut-to-fit stub at the flange allows a 90-degree prebent piece of tubing to clear the engine block, oil pan/filter, and suspension link arms.

The crossover pipe is scribed to tie into the passenger-side downpipe, then lead into the cat. This YJ has an OBD-II Vortec V-8, which wants signals from O2 sensors before and after the cat. Sensor bungs are added to the tubing in approximately the OE Chevy proximities.

Tubing wall thickness also matters. Industry standard is 16-gauge/0.65-inch-wall. For aluminized systems, Wallach recommends thicker 14-gauge tubing for greater strength and to allow more margin of error with welder settings.

Bends are available in a wide variety of radii and degrees. For tight bends, Wallach recommends using "donuts": complete mandrel-bent circles that can be sliced and diced as required.

Mufflers: Three criteria come into play here. Budget is one-stainless steel mufflers cost more but last longer; a polished finish jacks up the price even farther. Sound quality (clips are available on many manufacturers' Web sites) and available space are the other two concerns, and they're related. The rule of thumb is that shorter mufflers are louder. However, they offer greater mounting and routing flexibility. Glasspacks are enjoying a popularity resurgence, but their fiberglass packing retains moisture and rots faster than most "turbo"-style mufflers. Glasspacks also tend to hang lower and attract more rocks.