HKS Hi-Power Cat-Back Exhaust for 02-05 Honda Civic Si

HKS Hi-Power Cat-Back Exhaust, 60mm for 02-05 Honda Civic Si (EP3) K20A3

The EP3's factory exhaust is built to be quiet. The mufflers and resonator route the exhaust through chambers and around corners to cancel out noise, and each of those turns costs a little flow. On the K20A3, which likes to rev, that shows up most at the top of the tach. HKS's Hi-Power cat-back replaces everything from the catalytic converter back with 60mm mandrel-bent stainless piping and an offset muffler. The pipe takes the straightest path it can, and the exhaust gets out with less resistance.

You'll gain some high-RPM pull and sound, but don't expect a big power jump on its own. On a stock K20A3, the factory exhaust manifold is a bigger restriction than anything behind the cat, so a header and tune are what unlock real power. HKS points out the Hi-Power's flow capacity keeps up as the engine gets more built, and that's the real case for it. Add a header, intake, and tune later, and this exhaust won't be what's holding you back. Running a turbo-swapped EP3? It'll flow plenty for that, too.

Offset Muffler, Mandrel-Bent Pipe

Most mufflers sit right in line with the pipe, so the pipe has to curve around to reach them. HKS offsets the muffler to the side so the piping can run almost straight, and the design comes out of HKS's Japanese GT racing work. The pipe is mandrel-bent. A cheap exhaust gets bent in a way that crushes the pipe flat at each bend, which narrows it right where flow is already struggling. Mandrel bending keeps the full 60mm (2.36in) diameter all the way through each curve. Inside, the muffler is straight-through: a perforated core wrapped in packing, with no baffles for the exhaust to bounce off.

Sound and the Silent Version

A straight-through muffler is louder than stock. Expect a noticeable rasp at full throttle, and maybe some drone at highway speeds. If that's more than you want, HKS makes a Silent Hi-Power version for some cars. It has a silencer built into the muffler to quiet it down. Check whether it's offered for the EP3 before you order, and check your local noise laws.

SUS304 Stainless

The system's built from SUS304 stainless steel, the standard 18/8 grade, so it won't rust out even where roads get salted. That's a big deal on a car this old. A lot of EP3s are still running factory mufflers that are rusting through. The finish is plain silver, and near the front of the system it'll pick up some blue and gold heat tint over time. That's normal for stainless.

Install Notes

It bolts on behind the factory cat, using the stock hangers, and the catalytic converter stays in place. Expect the factory bolts at the cat flange to fight you on a car this age. Soak them with penetrating oil the night before, and have a replacement bolt set ready in case one snaps. Use a new gasket at the flange. Hang the system loosely first, line up the tip in the bumper, then tighten everything from front to back. Check for leaks and rattles once it's warmed up.

Fitment

• 2002-2005 Honda Civic Si hatchback (EP3) - K20A3
• Cat-back: replaces everything from the catalytic converter rearward
• Does not fit 2001-2005 non-Si Civic sedans or coupes