Maximize NA Power: 4-1 Stainless Steel KA24DE Headers & Downpipe
If you're building an S13, you already know the factory cast iron exhaust manifold is a massive bottleneck. The Flashark KA24DE headers and downpipe combo is engineered specifically to fix that. Designed for the 1991-1994 Nissan 240SX 2.4L DOHC, this 4-1 stainless steel exhaust system dramatically reduces backpressure, giving your KA engine the breathing room it needs to make real naturally aspirated (NA) power.
By pairing precision mandrel-bent tubes with smooth transitions, this setup maximizes exhaust scavenging. The result? A sharper throttle response, noticeable mid-to-top-end horsepower gains, and an aggressive exhaust tone that actually sounds like a proper JDM build.
Why Upgrade Your 240SX Exhaust?
- Optimized Flow (4-1 Design): Unlike the restrictive factory KA24DE exhaust manifold, our 4-1 tubular header design merges all four cylinders into a single collector. This optimizes exhaust gas velocity, ideal for peak horsepower on the track or street.
- Direct Bolt-On Fitment: No cutting or custom fabrication required. This header and downpipe system mounts perfectly to the S13 chassis and lines up with most aftermarket 240SX exhaust setups.
- Built to Last: Constructed from mirror-polished stainless steel to resist corrosion and handle extreme exhaust gas temperatures (EGTs).
- O2 Sensor Ready: Includes a pre-welded O2 sensor bung so your ECU maintains proper air/fuel ratios without throwing check engine lights.
Specifications:
-
Brand Name: Flashark
-
Certificate: ISO9001:2000
-
Application: Exhaust Header & Downpipe
-
Material: Stainless Steel
-
Surface: Mirror Polish
-
Placement on Vehicle: Front (Replaces factory header and downpipe)
-
Header Inlet / Outlet Size (IN): 1.75" / 2.5"
-
O2 Sensor Bung Included: Yes
- Header Style: 4-1 Exhaust System
Tuner's Guide: Headers vs. Downpipe vs. Exhaust Manifold
We get a lot of questions about exhaust terminology. Here is what you need to know for your KA24DE build:
- Exhaust Manifold vs. Header: The stock KA24DE exhaust manifold is a heavy, cast-iron log. It's cheap to manufacture but terrible for airflow. A header (like this one) uses individual, equal-length steel tubes for each cylinder. It's lighter and forces exhaust gases out faster, eliminating exhaust turbulence.
- Headers vs. Downpipe: The header bolts directly to the engine block to collect exhaust gases. The downpipe connects the bottom of the header to the rest of your exhaust system (usually the catalytic converter or test pipe). Because our kit includes both the KA24DE header and the downpipe, you won't have to worry about mismatching flanges or hunting for separate parts. You get a complete, leak-free front exhaust solution.
-
Critical Fitment Rule: For 2.4L KA24DE DOHC Inline-4 Engines ONLY | ❌ NOT compatible with KA24E SOHC engine variants
-
Verified Engine Fitment: 1991-1994 Nissan 2.4L KA24DE DOHC I4 Factory Original Engines
-
Verified Vehicle Fitment: 1991-1994 Nissan 240SX (S13 Chassis, Coupe & Hatchback body styles)
Q1: Will this header fit the single-cam 1989-1990 Nissan 240SX KA24E?
A1: No. This header is engineered strictly for the 1991-1994 Nissan 240SX equipped with the 2.4L KA24DE (DOHC) engine. The exhaust port layout on the single-cam KA24E cylinder head is completely different and will not match these flanges.
Q2: Does this kit include both the KA24DE headers and the downpipe?
A2: Yes! Unlike some competitors where you have to piece things together and worry about mismatched flanges, this Flashark kit includes both the 4-1 tubular header and the matching downpipe, giving you a complete, leak-free front exhaust solution.
Q3: Will installing this throw a Check Engine Light (CEL)?
A3: It shouldn't! We've welded an O2 sensor bung directly into the piping in the exact factory location. As long as your existing oxygen sensor is functional and reinstalled securely, your ECU will read the air/fuel ratios properly without triggering a check engine light.
Q4: Will this bolt up directly to my factory catalytic converter?
A4: Yes, the downpipe features a standard 2.5" outlet flange designed to mate perfectly to your S13's factory catalytic converter, as well as most aftermarket 2.5" test pipes or high-flow cats.
Q5: Do I need to buy new gaskets and hardware for the installation?
A5: The kit includes basic aftermarket hardware and gaskets to get the job done. However, from a tuner's perspective, we always highly recommend picking up a brand-new OEM Nissan multi-layer steel exhaust manifold gasket to ensure the absolute best and most durable seal against the engine block.
Q6: Can I use this KA24DE exhaust manifold replacement on an S14 (1995-1998)?
A6: While the header portion will bolt flawlessly to the S14's KA24DE engine block, the downpipe's angle and length are specifically tailored for the S13 chassis. It is not a direct bolt-on for the S14 without custom cutting or modification to your exhaust mid-pipe.
Q7: Why choose a 4-1 header design over a 4-2-1 setup for my S13?
A7: A 4-1 exhaust system merges all four primary tubes directly into a single collector. This design is highly favored by engine builders because it maximizes exhaust scavenging velocity at higher RPMs, resulting in better peak horsepower—perfect for track days, drifting, and aggressive street driving.
Q8: Does the installation require any cutting or custom welding?
A8: Absolutely not. This header and downpipe combo is a 100% direct bolt-on upgrade. You can unbolt your heavy, restrictive factory cast iron manifold and bolt this straight in using standard hand tools. (Pro tip: Soak your old factory bolts in WD-40 or penetrating oil overnight before removing them!)
Q9: How will this upgrade affect the exhaust sound of my 240SX?
A9: Replacing the thick cast iron manifold with thinner, mandrel-bent stainless steel tubes completely transforms the exhaust note. You will notice a significantly deeper, raspier, and more aggressive tone that screams classic JDM styling, especially when paired with an aftermarket cat-back system.
Q10: Will the mirror-polished stainless steel change color over time?
A10: Yes, and that is a badge of honor in the tuning community! Due to the extreme exhaust gas temperatures (EGTs) naturally produced by the KA24DE, the T-304 stainless steel will "heat cycle" and develop a beautiful golden, blue, or purple patina over time. This is completely normal and does not affect structural integrity.
Q11: Will I actually feel a noticeable difference in horsepower?
A11: Definitely. The factory KA24DE exhaust manifold is widely known as a massive bottleneck. By increasing the tubing diameter and smoothing the flow with mandrel bends, backpressure is severely reduced. You will feel a much sharper throttle response and noticeable mid-to-top-end naturally aspirated (NA) power gains.