FL5 Downpipe Guide: Catted vs Catless, CEL Risk, Daily Drivability (and the Best Options to Consider)
The FL5 Civic Type R responds extremely well to exhaust flow improvements, but a downpipe is also one of the quickest ways to change sound, smell, heat, and your odds of seeing a check engine light (CEL). This guide breaks down what actually changes, what to expect on a stock tune, and how the most common FL5 downpipe options compare.
Quick takeaways (if you just want the answer)
- Best daily path: a quality high-flow catted downpipe with proven fitment + good heat management.
- Lowest CEL risk: designs that intentionally support rear-O2 readiness (and don’t shove the catalyst too far downstream).
- Most power potential: any good downpipe + a proper tune. On a stock ECU, peak gains are often modest.
- Most aggressive sound & smell: catless (and typically the highest “odor/CEL/headache” combo for a street car).
Catted vs Catless on the FL5: what really changes
1) Sound (volume + tone)
- Catted: louder than stock, typically deeper, usually easier to live with day-to-day.
- Catless: noticeably louder and sharper; on louder exhausts it can become “too much” fast.
2) Smell / cabin comfort
- Catted: minimal odor once warm (varies by catalyst quality and calibration).
- Catless: raw exhaust odor is common, especially cold start and stop-and-go.
3) Heat management
A downpipe sits in one of the hottest parts of the FL5 engine bay. If you track the car or live in a hot climate, plan for ceramic coating, a turbo/downpipe blanket, and/or retaining OEM heat shields when possible.
Some designs retain OEM heat shield mounting points; others don’t — so heat management strategy can depend on the exact downpipe.
4) Power (stock tune vs tuned)
Most dyno charts online are on tuned cars. On a stock ECU, peak gains can be smaller than people expect. Once calibration is optimized (airflow, boost control, fueling), a downpipe usually becomes a stronger “multiplier.”
Stock-tune reality (manufacturer-provided): MST shared testing suggesting modest peak gains without tuning, with more meaningful gains once the car is properly calibrated. (Results vary by dyno, conditions, fuel, and vehicle.)
My honest take on “marketplace” downpipes (eBay / AliExpress / Alibaba)
I’m going to be straight, but professional: downpipes are not where I like gambling on unknown manufacturing. They live in a high-heat, high-vibration area and directly impact sealing, O2 sensor behavior, and catalyst efficiency monitoring. If a listing doesn’t clearly document material grade, weld/back-purge process, catalyst specs, and fitment tolerances, the buyer is basically doing the product validation.
- Materials & welds: stainless grade, flange thickness/flatness, and back-purging often aren’t verifiable.
- Catalyst claims: “high-flow cat” listings may not specify substrate type, cell count, core length, or thermal rating.
- Sensor placement: O2 bungs placed in turbulent zones can increase nuisance-code likelihood on some setups.
- Fitment variance: misalignment can create leaks, contact points, or installation stress.
In many cases, the cost savings rarely offsets the time and frustration if fitment or durability isn’t there. The FL5 is a serious platform — it deserves parts with consistent manufacturing and clear specs.
5) CEL risk (the practical explanation)
CEL risk is primarily influenced by rear-O2 catalyst efficiency checks and how consistently the ECU sees the catalyst “doing its job.”
- Highest risk: catless (or very small/low-efficiency cats).
- Medium risk: many 200-cell “race cats,” depending on placement and tune strategy.
- Lowest risk: high-quality catalysts designed for heat, placed near OEM location, with sizing that supports readiness.
Some products explicitly claim “no tune required / no CEL.” Those outcomes depend on catalyst selection, placement, and design — and real-world results can still vary by vehicle and mod combination.
Catless + boost control (blunt, real-world note)
In plain English: sometimes the car can run past boost targets (boost creep/overboost) and the tuner has to manage it. Can a tuner tune around it? Often yes. Is it always ideal for a street car? Not always — it depends on setup, climate, and how hard the car is being pushed and many other factors.
Best options by goal (my honest “buying guide”)
These aren’t “absolute rankings.” Results depend on the individual car, supporting mods, tuning, fuel quality, climate, and local emissions requirements. But this reflects what typically works best on a street-driven FL5 based on design intent, common outcomes, and real-world priorities.
Best Daily Driver (lowest headache)
CattedComfortLower CEL risk- MST 300-cell Catted — daily-driver focused positioning with “no CEL / no odor” messaging + published stock-ECU testing notes (manufacturer-provided).
- TSP High Efficiency — large 400-cell GESI-style catalyst and “no tune required / no CEL” claim (manufacturer-provided). Great daily-minded alternative under the MST category.
Reminder: heat management matters on all of them (shielding/blanket/coating).
Best Quality + All-Around (street + track with a tune)
CattedTrack-capableQuality-first- RV6 High Temp Catted — consistently one of the best “all-around” choices when you want premium build quality, strong fitment intent, and a catalyst designed for heat. With supporting mods + a proper tune, it’s a great street/track balance.
Best Track-First (flow + response mindset)
Track biasTune expectedHeat focus- Milltek SSXHO239 (De-cat) — large-bore catless approach, commonly positioned for motorsport/off-road use. Very track-focused.
- Dream Automotive De-cat — motorsport/off-road positioning with optional heat-management choices (hard lagging / Zircotec coating). Great if you want track-first + heat control options.
Most Aggressive (sound + rawness)
LoudestMost odorHighest CEL risk- Milltek SSXHO239 (De-cat) — louder, sharper tone and more pronounced turbo character vs most catted setups.
- Dream Automotive De-cat — similarly aggressive; heat-management options can help keep temps under control when driven hard.
Catless setups are commonly sold for off-road/motorsport use only. Expect more smell and higher CEL likelihood on street setups.
SBX Performance downpipe (in development)
Transparency: SBX’s FL5 downpipe is currently in initial design, testing, and validation. Fitment, heat management, sensor behavior, and repeatability are being evaluated before finalizing specs.
- 3.5" main flow path (not 4") with an optimized bellmouth transition
- Large metallic high-flow catalyst (5.0" body, optional 6.0" body being evaluated)
- OEM+ fitment and compatibility with OEM and common aftermarket front pipes
- Sensor placement intended to support rear-O2 stability
- Heat shield provisions and serviceable hardware layout
When testing is complete, finalized specs and validation notes will be published (including what changed during testing).
FL5 Downpipe Options (Catted + Catless)
SBX Performance (in testing)
CattedIn validation- Cat type: High-flow metallic (large body)
- Daily: Target: excellent
- CEL risk: Target: low
- Notes: 3.5" main path + large metallic catalyst; final specs pending testing
MST 300-cell Catted
CattedDaily focus- Cat type: 300-cell high-flow (large cat body)
- Daily: Excellent
- CEL risk: Very low (claimed)
- Notes: Published stock-ECU testing notes; positioned “no CEL / no odor” (manufacturer messaging)
Two Step Performance (TSP) High Efficiency
CattedDaily-minded- Cat type: 5.0" 400-cell GESI (claimed)
- Daily: Excellent
- CEL risk: Very low (claimed)
- Notes: No tune required + “no CEL” claim; heatshield fitment variance noted on some batches; blanket commonly recommended
RV6 High Temp Catted
CattedStreet/track- Cat type: 300-cell high-temp metallic
- Daily: Excellent
- CEL risk: Medium
- Notes: High-temp cat + cast transitions; OEM heatshield mounts retained; premium QC reputation
MAPerformance Downpipe (HDAXIR-DPC)
CattedDirect-fit- Cat type: High-flow catted (500 hp rated)
- Daily: Good
- CEL risk: Medium
- Notes: 3" stainless from turbo tapering to factory connection after the cat; install hardware + O2 extension included; coating option; limited lifetime warranty
Milltek SSXHO291 (Twin Cat “No CEL” version)
CattedPremium UK- Cat type: HJS high-flow sports cat (twin-cat)
- Daily: Very good
- CEL risk: Low–Medium (claimed)
- Notes: 3" (76.2mm) cast DP; “No CEL” twin-cat configuration described in listings; outcomes can vary by setup
Milltek SSXHO292 (200-cell Race Cat)
CattedRace cat- Cat type: HJS 200-cell race cat
- Daily: Good
- CEL risk: Medium–High
- Notes: 3" (76.2mm) cast DP; “race product” positioning; check local compliance rules
Milltek SSXHO239 (Large-bore DP + De-cat)
CatlessTrack-first- Cat type: Catless
- Daily: Aggressive
- CEL risk: High
- Notes: 3" (76.2mm) de-cat; motorsport/off-road positioning; tuning commonly required
27WON High-Flow Catted
CattedTune recommended- Cat type: 200-cell metallic
- Daily: Good
- CEL risk: Medium–High
- Notes: Retains OEM heatshield points; “CEL can be illuminated”; tuning strongly recommended
Scorpion SHDX017 (High-Flow Catalyst)
CattedUK-made- Cat type: 200-cell sports cat
- Daily: Good
- CEL risk: Medium–High
- Notes: 3.5" tubing; Stage 2 calibration commonly recommended
Invidia (HFC variant)
CattedConfirm SKU- Cat type: High-flow cat
- Daily: Good
- CEL risk: Medium
- Notes: Part numbers/contents vary by region; confirm FL5 fitment + included hardware
PLM “Power Driven” Catted
CattedBudget- Cat type: High-flow metallic (varies)
- Daily: Budget-friendly
- CEL risk: Medium–High
- Notes: Lower price point; mixed feedback; inspect fitment/welds/flanges before install
Axion Industries “2N1” combo
Catted + CatlessV-band- Cat type: Catted + swappable catless section
- Daily: Usage-dependent
- CEL risk: High
- Notes: Swapping can get harder with heat-cycled hardware over time; OEM upper heat shields not compatible (per manufacturer); blanket recommended Over time especially in wet/salty climates V-band clamps and the mating flanges can heat-cycle, corrode, and “stick,” so what starts as a quick-swap setup can turn into a maintenance item (anti-seize, periodic inspection/retorque) and, if neglected, may increase the chance of small exhaust leaks.
Dream Automotive (De-cat)
CatlessHeat options- Cat type: Catless
- Daily: Aggressive
- CEL risk: High
- Notes: Motorsport/off-road positioning; optional hard lagging or Zircotec coating; lightweight emphasis
Ballade Sports (3" / Titanium)
CatlessOff-road note- Cat type: Typically off-road (catless)
- Daily: Aggressive
- CEL risk: High
- Notes: 3" outlet designs; manufacturer states fitment revisions; verify current revision + real-world FL5 feedback
Tsudo / SPDZ1 Catless Options
CatlessValue- Cat type: Catless
- Daily: Aggressive
- CEL risk: High
- Notes: Value-focused; confirm materials, weld quality, sensor provisions, and shipping/compliance rules
| Downpipe | Cat type | Daily drivability | CEL risk (typical) | Notes |
|---|---|---|---|---|
| SBX Performance (in testing) | High-flow metallic | Target: excellent | Target: low | 3.5" main path + large metallic catalyst; final specs pending testing |
| MST 300-cell Catted | 300-cell high-flow | Excellent | Very low (claimed) | Published stock-ECU testing notes; “no CEL / no odor” messaging (manufacturer) |
| TSP High Efficiency | 5.0" 400-cell GESI (claimed) | Excellent | Very low (claimed) | No tune required + “no CEL” claim; heatshield fitment variance noted on some batches |
| RV6 High Temp Catted | 300-cell high-temp metallic | Excellent | Medium | Cast transitions; OEM heatshield mounts; premium QC reputation |
| MAPerformance (HDAXIR-DPC) | High-flow catted (500 hp rated) | Good | Medium | 3" taper to factory connection; hardware + O2 extension; coating option; limited lifetime warranty |
| Milltek SSXHO291 | HJS sports cat (twin-cat) | Very good | Low–Medium (claimed) | 3" cast DP; “No CEL” twin-cat described in listings; outcomes vary |
| Milltek SSXHO292 | HJS 200-cell race cat | Good | Medium–High | 3" cast DP; race positioning |
| Milltek SSXHO239 | Catless | Aggressive | High | 3" de-cat; motorsport/off-road positioning |
| 27WON | 200-cell metallic | Good | Medium–High | OEM heatshield points; CEL can happen; tune recommended |
| Scorpion SHDX017 | 200-cell sports cat | Good | Medium–High | 3.5" tubing; Stage 2 commonly recommended |
| Invidia (HFC) | High-flow cat | Good | Medium | Confirm FL5 SKU + included hardware |
| PLM Power Driven | High-flow metallic (varies) | Budget-friendly | Medium–High | Mixed feedback; inspect before install |
| Axion 2N1 | Catted + catless section | Usage-dependent | High | Swap concept; heat-cycled hardware may add maintenance; blanket recommended |
| Dream Automotive De-cat | Catless | Aggressive | High | Heat management options (hard lagging / Zircotec); lightweight emphasis |
| Ballade Sports | Typically catless | Aggressive | High | Revision/fitment claims; verify current production |
| Tsudo / SPDZ1 | Catless | Aggressive | High | Value-focused; confirm materials/welds/compliance |
Deep dives
RV6 High Temp Catted Downpipe
Top qualityStreet/track- Specs: 300-cell high temperature cat; 304 stainless precision cast transitions; 3.0" outlet; TIG welded; argon back-gassed; OEM heatshield mounting points maintained.
- Includes: 3 chromoly studs, 3 locking nuts, graphite gasket with sealing ring.
- Warranty: 24 months on castings and welding (no warranty on catalytic converters).
- Coating note: ceramic coating adds ~7–14 business days processing.
- Review: “Definitely one of the best purchases… completely different car… ceramic coated in black looks amazing!” (Antonio Herrera, 12/26/2025)
- Review: “Straightforward install… be ready to struggle with bolts… silver ceramic coating helped heat… everything lined up nicely.” (Mike V., 12/26/2025)
My take: Best quality + best all-around street/track direction when paired with supporting mods and a proper tune.
MST 300-cell Catted Downpipe
Best dailyValue- Positioning: “No CEL guarantee,” “no odor,” designed to pass U.S. emissions (manufacturer messaging).
- Stock-tune testing (provided): small peak gain on stock ECU; realistic ~8–10 hp range in their shared notes (varies by dyno/conditions).
- Daily-driver appeal: sets expectations honestly for stock ECU while still supporting tuning later.
My take: If someone wants a daily-friendly catted option that’s priced sensibly and sets real expectations, this is a standout on paper based on the info provided.
Two Step Performance (TSP) “High Efficiency” Downpipe
Daily-mindedBig cat- Key notes: 5.0" 400-cell GESI-style cat; cast ends; includes gaskets/hardware; O2 extension; heat-shield standoffs.
- Manufacturer statement: “No ECU calibration required” and “will NOT result in a check engine light.”
- Fitment note: some users report heatshield bolt hole alignment differences; blanket commonly used as a solution.
- Review: “This is how the car should have came… opens the car up… Plus there’s no CEL!” (Noah Pfeil, 11/27/2025)
- Review: “Heat shield bolt holes are off, but I drilled them… overall very pleased.” (James, 11/21/2025)
My take: Solid “daily-friendly” option under the MST category — especially for owners prioritizing low-CEL intent and a large catalyst design.
MAPerformance Downpipe (HDAXIR-DPC)
Direct-fitDealer-friendly- Construction: 304 stainless, hand TIG welded (per listing).
- Design: 3" stainless from the turbo tapering to the factory connection after the cat (per listing).
- Catalyst: high-flow cat rated for 500 horsepower (per listing).
- Included: install hardware + oxygen sensor extension (per listing).
- Finish: coating option available (per listing).
- Warranty: limited lifetime warranty (per listing).
My take: A practical, straightforward catted upgrade with complete install hardware and a direct-fit approach.
Milltek SSXHO291 (Twin Cat / “No CEL” listing language)
CattedPremium UK- Type: cast downpipe with HJS high-flow sports cat (twin-cat configuration per listing language).
- Diameter: 76.2 mm (3").
- Notes: often described as “No CEL” in the twin-cat configuration; real-world outcomes can still vary by car/setup.
My take: If someone wants a premium catted option, this is the “daily-leaning” Milltek direction — just confirm the exact SKU/config.
Milltek SSXHO292 (HJS 200-cell Race Cat)
Race catMore aggressive- Type: cast downpipe with HJS 200-cell race cat.
- Diameter: 76.2 mm (3").
- Notes: race positioning is common; typically louder + higher CEL likelihood than daily-focused catted designs.
My take: A more performance/sound-forward “race cat” style option vs the SSXHO291.
Milltek SSXHO239 (Large-bore Downpipe + De-cat)
CatlessTrack-first- Type: large-bore downpipe + de-cat (catless).
- Diameter: 76.2 mm (3").
- Notes: motorsport/off-road positioning; heat management strongly recommended; tuning commonly required.
My take: One of the cleanest “track-first / aggressive sound” directions if someone is intentionally going catless.
Dream Automotive De-cat Downpipe
CatlessHeat options- Positioning: motorsport/off-road use only (per listing).
- Heat management choices: no heat management, hard lagging, or black Zircotec ceramic coating (per listing).
- Hard lagging note: described as handling up to ~1200°C (per listing).
- Weight (listed): ~2.7 kg without heatshield / ~3.0 kg with heatshield.
My take: Great track-first option for people who want catless flow and are thinking about heat control from day one.
Axion Industries “Evolution 2N1” (catted + swappable catless)
V-band swapMaintenance-aware- Concept: catted street section + swappable catless race section using V-band clamps.
- Heat note: OEM upper heatshields cannot be installed (per manufacturer); blanket recommended.
- Practical reality: V-bands can seal extremely well, but repeated removal/installation + heat cycles (especially in wet/salty climates) can make service harder over time and may require maintenance (anti-seize, inspection, retorque).
- Review: “Welds are superb… one of a kind… easily swappable… great quality!” (provided review snippet)
Invidia Down Pipe w/ High Flow Cat
CattedConfirm SKU- Fitment: FK8 (2017–2021) / FL5 (2022–present) (per listing).
- Design: intended to replace the factory downpipe (commonly described as a major restriction after the turbo).
- Brand positioning: balancing backpressure and exhaust gas velocity (not simply bigger diameter).
- Manufacturing: robotic welding mentioned for uniformity (per listing).
- Warranty: limited lifetime on structural welds/cracks/manufacturing defects; catalytic converter stated as 2 years (per listing language).
- Practical note: confirm exact FL5 part number and included items (hardware/gaskets/O2 extensions) since retailer packages can vary.
Ballade Sports (BS-FK8-DP / BS-FK8-TIDP)
CatlessOff-road note- Products: 3" Down Pipe (BS-FK8-DP) + 3" Titanium Down Pipe (BS-FK8-TIDP).
- Construction: 304 stainless (DP) / Grade 5 titanium (Ti DP) (per listing).
- Geometry: 3-7/8" opening tapering to 3" outlet; pie-cut bends on titanium version (per listing).
- Heat shields: retains factory heat shields (per listing).
- Manufacturing: fully back-purged (per listing).
- Use note: off-road use only language included (per listing).
- Practical note: Ballade claims fitment revisions; verify current revision and included hardware before purchase.
Tsudo Resonated Downpipe (01-1235-DP)
ValueResonated- Construction: 304 stainless steel (per listing).
- Design: cast iron bell-mouth + resonated pipe to reduce rasp and refine tone (per listing).
- Heat shields: retains OEM heat shield mounting points (per listing).
- Install: includes hardware and gasket (per listing).
- Compliance/shipping: off-road use only language + restrictions noted for CA/NY on the listing (verify current rules and local laws).
PLM “Power Driven” Catted
Budget cattedInspect before install- Specs (provided): TIG-welded 304 stainless; high-flow metallic core cat; includes gasket & hardware; one-year warranty.
- Reality: purchased often due to pricing; feedback can vary by platform and setup.
- Practical advice: inspect flange flatness, weld consistency, and sensor bung placement before installation.
Daily-driver install notes (that save you headaches)
- Turbo hardware: soak studs/nuts ahead of time with penetrating oil; turbo fasteners are heat-cycled and can be stubborn.
- O2 sensor routing: some kits include extensions; others may require them depending on bung location and harness routing.
- Heat shields vs blankets: if OEM shields don’t fit on a specific batch/version, a quality blanket can be a practical alternative (especially for track use).
- Plan the next steps: downpipes are commonly paired with intake/intercooler/front-pipe/exhaust changes — best results usually come with a tune once airflow mods stack up.
Shop the downpipes mentioned in this guide
Prefer the quick route? Here are direct links to the main options referenced above.
MST 300-Cell Catted Downpipe (FL5)
Daily-driver focused positioning (per manufacturer messaging).
View ProductRV6 High Temp Catted Downpipe (FK8/FL5/DE5)
High-temp metallic catalyst + OEM heatshield mounting points retained (per provided specs).
View ProductMAPerformance Downpipe (2022+ FL5)
Direct-fit catted option with included install hardware and O2 extension (per listing).
View ProductPLM Power Driven Catted Downpipe (FL5/DE5)
Budget-friendly catted option; verify fitment details and install prep as with any downpipe.
View ProductMilltek Cast DP w/ HJS Hi-Flow Sports Cat (No-CEL version)
Catted “twin-cat” configuration; verify goals and local compliance before purchase.
View ProductMilltek Cast DP w/ HJS 200-Cell Race Cat
More aggressive “race cat” style option; typically louder + higher CEL likelihood than daily-focused catted designs.
View ProductMilltek Large-Bore Downpipe + De-cat (Off-Road Only)
Maximum-flow catless option; off-road/motorsport positioning; heat management strongly recommended.
View Product