OBS Chevy Exhaust System Guide (1988–1998 GMT400 Silverado & Sierra)
Exhaust is one of the first things OBS owners change, and it’s easy to overspend or end up with a drone you can’t live with. This is a straight guide to how the GMT400 exhaust is laid out, your real options, and how to pick a setup that sounds good without turning the cab into a resonance chamber.
Short version: most OBS trucks respond well to a cat-back or a full Y-pipe-back setup with a quality muffler. The muffler choice and tailpipe exit decide 90% of the sound. Bigger pipe is not automatically better on these small-block trucks.
Trucks, years and engines
- GMT400 / OBS: 1988–1998 Chevrolet and GMC C/K trucks and SUVs
- Common gas engines: 4.3 V6, 5.0, 5.7, and 7.4 (big block)
Setup and sound expectations differ by engine. A 5.7 and a 7.4 want different mufflers than a 4.3.
How the factory exhaust is laid out
From the engine back, an OBS truck runs manifolds (or headers if modified) into a Y-pipe, through the catalytic converter, into the muffler, and out the tailpipe. When people say “cat-back,” they mean everything from the cat rearward. “Y-pipe-back” or a full system goes further forward.
Where you cut in decides cost and effort:
- Muffler swap only: cheapest, quickest sound change
- Cat-back: balanced cost and result; new pipe, muffler, tailpipe
- Y-pipe-back / full: most involved; best for headers or a big-block
Choosing a muffler (this is the real decision)
The muffler sets the character:
- Chambered mufflers give the classic aggressive small-block bark. Can drone on the highway depending on the truck.
- Straight-through / performance mufflers flow well and are usually less droney, with a smoother tone.
- Larger-body mufflers tend to deepen the sound and cut drone versus a small glasspack-style unit.
Owners commonly reference specific muffler families (for example a MagnaFlow straight-through) when they want deep-but-livable. Match the muffler to your engine and how you use the truck — a daily-driven 5.7 has different needs than a weekend big-block.
Pipe diameter — don’t oversize
On a stock or mildly modified small-block OBS, 2.5″ is the common sweet spot. Jumping to 3″+ on a low-output engine can hurt low-end scavenging and add drone without a real gain. Size the pipe to the engine, not to the look.
Single vs. dual
- Single exhaust is simpler and quieter, fine for a stock or mild truck.
- Dual exhaust looks and sounds the part, costs more, and needs room around the spare and rear axle. On a big-block it makes more sense than on a 4.3.
Common mistakes and bad advice to avoid
- Buying pipe that’s too big for the engine. Bigger isn’t better on a stock small-block.
- Chasing a sound clip. Cab acoustics, engine, and cam all change how a muffler sounds on your truck.
- Ignoring drone until it’s installed. If you road-trip the truck, weight your choice toward a straight-through or larger-body muffler.
- Cheaping out on hangers and clamps. A good system rattles and leaks if it’s hung wrong.
What to verify after install
- No exhaust leaks at the flanges and clamps (listen and feel on a cold start)
- Adequate clearance from the frame, fuel/brake lines, spare and axle
- Tailpipe exit is secure and pointed where you want it
- Cabin drone is acceptable at highway speed before you call it done
FAQ
What pipe size for a stock 5.7 OBS?
2.5″ is the usual sweet spot. Save 3″+ for a built engine.
How do I get a deep sound without drone?
Lean toward a larger-body straight-through muffler and avoid oversizing the pipe. Chambered mufflers sound meaner but can drone.
Cat-back or full system?
Cat-back is the best value for most owners. Go further forward only if you’re running headers or a big-block.
Will an exhaust add power?
On a stock small-block, expect sound and a small gain at best. Real power comes with heads, cam and tuning.
Discuss this in the FullSizeChevy forum
Tell us your engine, pipe size, and muffler — and whether it drones. Post a cold-start clip if you’ve got one.
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