Which header system is best for a 2003 4.8 Silverado 1500, and are shorty headers worth it?

We haven't verified specific header part numbers for the GMT800 4.8, so check each maker's application list for your cab, bed and drive.

Are shorties worth it? Modestly. Shorties generally flow better than the stock manifolds, but they almost always make less power than long tubes because the primaries are short and unequal. On a stock 4.8 the gain is small either way. Speedway's rough generalization is 5 to 20+ hp from aftermarket headers, with the bigger gains on heavily modified engines that move a lot of air. How much you get depends on displacement, compression, cam and tune.

Type	Good at	Trade-off
Long tube	Most power; best scavenging	Needs room and ground clearance for the collectors
Shorty	Fits tight or lowered chassis	Almost always less power than long tubes (short, unequal primaries)
Stock / performance cast manifold	Compact, fits, low maintenance, quieter	Least flow; performance manifolds are a compromise

On an EFI engine, a tune helps you get the full benefit from headers. Check local emissions rules before removing factory parts.