PRODUCT DETAILS
HKS Sport Cat-Back Exhaust (LES-H05) - 1989-1991 Honda Civic Si (D16A6)
The EF Si is a light car with a modest engine, which means the exhaust has a specific job: get gases out without killing the velocity that makes a small D-series feel alive. HKS sized this system for exactly that. 50mm piping into a 60mm R-2 tip, with a muffler designed to broaden the torque band rather than just chase a peak number.
50mm Is The Right Size, Not The Small Size
Worth explaining, because people see the number and assume bigger would be better.
Exhaust gas needs velocity as well as volume. Velocity is what creates the scavenging effect that helps pull spent gases out of the cylinder, and it's what keeps a small naturally aspirated engine responsive down low.
Oversize the piping on a 1.6 liter and that velocity drops. What you get is a car that might show a marginally higher peak number on a dyno and feels worse everywhere you actually drive, with a hollow note to match.
50mm keeps velocity where the D16A6 lives while still flowing considerably better than the restrictive factory system. HKS sizes these per application rather than applying one pipe diameter across their range, and that's why.
Wider Torque Band, Not Just Peak Power
The muffler design matters as much as the piping.
HKS builds the Sport series around reducing backpressure while maintaining the characteristics that make a car pleasant to drive. That means low-end torque stays intact while the top end opens up, rather than trading one for the other.
On an EF, that's the right priority. These cars weigh nothing, so usable torque through the midrange is what makes them quick on a back road. A system that only helps above 6,000 rpm isn't helping much of the time.
The Gains Build With Your Build
Honest framing on what to expect.
On a completely stock D16A6, a cat-back is a modest improvement. The engine isn't producing enough exhaust volume to fully use a freer system, and anyone promising big numbers from an exhaust alone on a 1.6 is overselling it.
Where it earns its keep is as the build progresses. Add an intake, a header, or cams, and the exhaust goes from adequate to the limiting factor. This has the capacity ready for that, which is why it's the sort of system people keep as the car develops rather than outgrowing.
And in the meantime, the car sounds considerably better than it did.
Fitment
1989-1991 Honda Civic Si hatchback (D16A6)
Part number LES-H05.
Who Should Run This Exhaust
This is for the EF owner who wants a real name-brand system rather than a generic cat-back, and who appreciates that sizing matters more than size. HKS has been building these since these cars were new, the 50mm piping is correct for the engine rather than the biggest pipe that fits, and the tone suits the car. Bolt it on and enjoy it.
Fits: 1989-1991 Honda Civic Si hatchback (D16A6). Part number: LES-H05. Type: cat-back exhaust system. Piping: 50mm. Tip: 60mm, R-2 style.
1989-1991 Honda Civic Si Hatchback