Custom Exhaust System Build - You Tube

Lots of in-and-out is necessary for custom systems in tight confines. Wallach makes the cope in the passenger-side downpipe where it mates to the crossover pipe with a grinder.

Lots of in-and-out is necessary for custom systems in tight confines. Wallach makes the co

Tailpipes: Resist the temptation to call it quits at the muffler (unless using glasspacks with integrated turnouts). Tailpipes should always be included: They channel deadly carbon monoxide away from the cab.

Headers/Exhaust Manifolds: Primary-tube clearance and collector dumping location are the main concerns. The three most common solutions to literally starting a custom exhaust are (1) finding an OE answer, (2) sourcing aftermarket "swap" headers, or (3) creating custom headers. In the OE realm, Chevy small-blocks are the ideal example of multiple manifold configurations for the same block: Car, truck, and Corvette manifolds vary in their dump locations. Research and possibly junkyard foraging are required. Less mind-numbing are swap headers. The aftermarket offers these for popular repowering combinations.

Odd-ball swaps can require starting from scratch. For example, someone who's dead-set on putting a Caddy big-block in a flatfender will likely face a few exhaust challenges. Luckily, header flanges are available for many engines. Existing headers can sometimes be modified and welded to these flanges. Alternately, build-your-own kits are available; a few companies even make custom headers.

Emissions: For vehicles that must pass "smog" testing, catalytic converters can add considerably to exhaust-system cost. Even ones that don't have to pass but have closed-loop computer-controlled engines need exhaust bungs for their O2 sensors.

American Offroad offers these hints, derived from 16 years of trying different approaches.

Tools: No bender or notcher is required. Wallach claims that tubing can be coped with a grinder in less time than it takes to set up a notcher. For cutting, he prefers a portaband or even a reciprocating saw over a chop saw.

Hardware: Use the thickest available flanges and hangers. Avoid parts-store exhaust hangers-source minimum 3/16-inch-thick hangers for durability. You'll also use fewer since heavier-duty hangers can support more weight.

Sealing: Prep flanges' mating surfaces on a belt sander with 80- or 100-grit paper. Use name-brand flange gaskets reinforced with Ultra Copper silicone gasket-maker. American Offroad double-nuts flange bolts as a third line of leak-defense.

System Design: Wallach prefers the cut-and-tack approach: "Eyeball the angles and keep cutting until it's right." For optimal flow, he recommends butt welds, which require all gaps to be less than 1/16 inch. Otherwise, the joints are susceptible to leaks, and the welds create heat-stress points at the tubing's edges. If using slip-fit swedged joints, always go male-into-female following the exhaust path. Otherwise, leading edges slow down exhaust flow.

Contrary to traditional thinking, true "dual exhaust" systems-where both sides are independent of each other-usually don't work as well as systems that have a balance tube/"H" pipe/crossover pipe. Since compression and exhaust scavenging vary among cylinders, tying the sides together equalizes the pressure. Performancewise, this smooths flat spots in the powerband and also controls back-rap that can result from abrupt deceleration.

Finishing Details: Stainless steel is virtually maintenance-free. People who want to send out their systems for thermal coatings should add flanged joints at accessible locations. For custom headers that will be thermal-coated, Wallach recommends TIG-welding all joints for aesthetics. Otherwise, a coat of high-temp spray paint makes aluminized tubing look finished and helps retard rust.

The photos here show highlights of American Offroad's custom 2.5-inch exhaust for a YJ that has a swapped-in Vortec V-8, an AX-15 transmission with remote-mounted slave cylinder, and a Black Diamond X2 long-arm suspension system. Short-wheelbase Jeeps' tighter confines present more logistical puzzles, but the overall approach and execution apply to all 4x4 custom-exhaust jobs.