RXP-X 300 Rear Exhaust Kit (2021–present) — Install Guide

GT40 Marine | SKU GT40-SD-EXH-RXP-2021P | Stainless Rear Exhaust + J-Pipe Delete | Rev 1.0 — 2026-05-24

Before You Start — Hull Year Decision Tree

This kit is NOT interchangeable with the 2016-2019 RXP-X 300 exhaust kit or the 2020 RXP transition unit. Verify hull year BEFORE opening any packaging:

| # | Hull HIN Year Code | Correct Kit |

|---|---|---|

| 1 | 2016, 2017, 2018, 2019 | Use GT40-SD-EXH-RXPX300-1619 instead |

| 2 | 2020 | See the 2020 RXP Transition Bulletin (GT40-SD-EXH-RXP-2020-BULLETIN) — small geometry change from 2021+ |

| 3 | 2021, 2022, 2023 | ✅ This kit |

| 4 | 2024+ | ✅ This kit fits 2024+ RXP-X 300 (NOT 325HP) |

| 5 | 2024+ RXP-X 325 | This kit DOES NOT fit. Use ST3 family for 325 exhaust |

If you are uncertain of your hull year, the HIN sticker is inside the rear storage bin — the 10th character of the HIN is the model year code per BRP convention.

Fitment

| Platform | Model | Year | Engine |

|---|---|---|---|

| Sea-Doo | RXP-X 300 | 2021–present | 1630 ACE 300 |

Not for: 2016-2019 RXP-X 300, 2020 RXP-X 300 (transition year), RXP-X 325HP, RXT-X, GTX, GTR, Wake Pro, Spark. Confirm hull HIN year (2021+) AND engine code (1630 ACE 300, NOT 325) before install.

In the Box

• (1) GT40 stainless steel rear exhaust outlet, hand-formed, mirror-polished, 2021+ RXP-specific geometry
• (1) GT40 J-pipe delete adapter, billet aluminum, anodized black
• (1) Stainless steel exhaust gasket, fire-rated, marine-grade
• (1) Water-injection adapter with check valve
• (6 ft) High-temperature silicone water hose, 3/4" ID
• (4) Stainless worm-gear hose clamps, #12
• (6) M10 × 35 mm SHCS — manifold mounting (high tensile, marine-grade)
• (6) M10 stainless flat washers
• (1) Hardware bag — spare gasket, spare clamps
• (1) High-temperature exhaust sealant tube, 4 oz
• (1) GT40 product registration card
• (1) This guide

Verify all components present before starting. Missing parts: support@gt40marine.com.

Tools Required

• 10 mm / 13 mm / 17 mm sockets + ratchet, 3/8" drive
• T25 + T30 Torx drivers
• 5 mm + 6 mm + 8 mm hex (Allen) keys
• 3/8" drive torque wrench, 10–60 Nm range
• Long extension bars (the 2021+ RXP rear-bay layout is deeper than 2016-19)
• Hose-clamp pliers
• Marine-grade exhaust sealant applicator (small brush)
• Flashlight or headlamp
• Shop towels
• Marine-grade copper anti-seize compound

Safety

Read in full before starting.

1. Battery disconnected for the duration of the install.
2. Cold engine only. Factory J-pipe retains heat for over an hour after operation.
3. Eye protection mandatory when working around the exhaust manifold.
4. Hand protection. Marine exhaust has sharp flange edges.
5. No smoking / open flame.
6. Two-person lift recommended for the stainless rear exhaust outlet positioning.
7. 2021+ RXP rear-bay note: the 2021+ hull has a tighter rear-bay envelope than the 2016-19 hull — plan extra time for the titanium outlet positioning step.

If you are not comfortable with PWC exhaust system work, take the install to a certified marine technician.

Pre-Install Checklist

• [ ] Watercraft on stable trailer or stand
• [ ] Hull HIN year verified — 2021, 2022, 2023, or 2024+ RXP-X 300 (NOT 325)
• [ ] Battery negative disconnected and isolated
• [ ] Engine bay clean and dry
• [ ] Factory J-pipe + waterbox routing photographed before disassembly
• [ ] Ribbon delete already installed if running Stage 2+ (GT40-SD-RDK-SD300)
• [ ] Marine-grade anti-seize ready
• [ ] 2.5 hours minimum for install + 2 hours sealant cure scheduled before first start

Step-by-Step Install

Step 1 — Access the Engine Bay (2021+ RXP Layout)

The 2021+ RXP-X 300 hull places the rear exhaust components under a more compact access point than earlier hulls.

1. Remove the seat
2. Lift the rear storage bin — the 2021+ bin is shaped differently from 2016-19; the lift sequence requires angling the bin upward 15 degrees before lifting straight
3. Remove the inner side panel on the port side to expose the J-pipe routing (this panel is held by 4 T25 Torx screws)
4. The 2021+ hull moved the access point inboard 50 mm vs 2016-19, so the J-pipe head is harder to reach from above — use a long extension

Disconnect the battery negative terminal. Secure the cable away from the post.

Step 2 — Remove the Factory J-Pipe and Rear Exhaust

The 2021+ RXP-X 300 uses BRP's revised exhaust system. Key changes vs 2016-19:

• The waterbox is slightly smaller and oriented 10 degrees off-axis
• The J-pipe-to-waterbox V-band clamp uses a different orientation
• The through-hull rear exhaust outlet uses a tighter approach angle than 2016-19

Removal sequence:

1. Disconnect cooling water injection lines feeding the J-pipe (2 small hose connections, spring clamps)
2. Loosen the J-pipe-to-manifold V-band clamp (13 mm) — orientation differs from 2016-19, the clamp head sits inboard
3. Loosen the J-pipe-to-waterbox V-band clamp (13 mm)
4. Lift the J-pipe out — heavier than 2016-19 (~8 lbs), the additional mass is added downstream attenuation
5. Disconnect the waterbox inlet/outlet
6. Lift the waterbox out — angled removal required, do not force it straight up
7. The through-hull rear exhaust outlet stays in the hull — only the internal pipe is being replaced

Set all stock components aside. Do not discard if you may sell the craft in stock form later.

Step 3 — Inspect and Clean the Manifold Outlet Flange

1. Wipe the manifold outlet flange clean with shop towels
2. Inspect the gasket surface — must be flat, no carbon scoring
3. Light scuff with 220-grit sandpaper if any surface contamination
4. Final wipe with a clean solvent wipe
5. Allow 60 seconds for full solvent evaporation

Step 4 — Install the GT40 J-Pipe Delete Adapter

1. Apply marine anti-seize to all 6 M10 × 35 mm SHCS threads
2. Position the supplied stainless gasket on the manifold flange
3. Apply a thin even bead of high-temperature exhaust sealant around the gasket's outboard face
4. Position the GT40 J-pipe delete adapter against the gasket — note the 2021+ adapter has a slight off-axis exit angle (10 degrees) to match the revised through-hull approach
5. Thread all 6 M10 SHCS through the adapter with flat washers — hand-tight only
6. Confirm the adapter is square to the manifold (no rotational offset)
7. Torque the 6 bolts to 42 Nm (31 ft-lb) in a star pattern across two passes
8. Wipe any sealant squeeze-out

Step 5 — Install the Stainless Rear Exhaust Outlet (2021+ Geometry)

The 2021+ outlet is geometrically distinct from 2016-19 — do not attempt to substitute parts between kits.

1. Apply marine anti-seize to the stainless outlet's mounting flange threads
2. Position the outlet against the J-pipe delete adapter's exit flange
3. Thread the supplied V-band clamp around both flange edges
4. Snug the clamp finger-tight
5. Rotate the outlet to align with the through-hull exit point — the 2021+ approach angle is tighter than 2016-19; align carefully
6. Once aligned, torque the V-band clamp to 22 Nm (16 ft-lb) in two passes
7. Verify the outlet exits the hull cleanly — no contact with hull fiberglass at any point
8. 2024+ hull note: 2024+ RXP-X 300 hulls (still 300HP, NOT 325) have one additional zip-tie support bracket on the through-hull approach — use the supplied UV-rated zip tie to secure the outlet to this bracket if present

Step 6 — Reintroduce Cooling Water Injection

1. Locate the cooling water source on the engine block (3/8" NPT port near the rear of the head — same location as 2016-19)
2. Locate the GT40 adapter's water injection port (top face of the J-pipe delete adapter)
3. Cut the supplied silicone water hose to length from source to injection point
4. Slide #12 clamps onto each hose end
5. Push the hose onto the source fitting, then the adapter water-injection port
6. Tighten both clamps to 3 Nm (27 in-lb) equivalent
7. Verify hose routing avoids contact with the hot exhaust adapter — minimum 25 mm clearance to any exhaust surface
8. The supplied check valve is integrated into the water injection adapter — no separate inline install needed

Step 7 — Allow Sealant Cure Time

Exhaust sealant requires a minimum of 2 hours cure time before engine start. Do not skip.

Overnight cure recommended for full strength.

Step 8 — Reassembly and First Start

After cure:

1. Walk the engine bay — every fastener, every clamp, every hose joint
2. Confirm no tools or hardware remaining
3. Reconnect the battery negative terminal — torque to 10 Nm (89 in-lb)
4. Reinstall the port-side inner panel removed in Step 1 (4 T25 Torx screws to torque 2.5 Nm)
5. Replace the engine bay hatch, storage bin, seat
6. Connect the engine cooling flush hose
7. Start the engine on the trailer
8. Idle for 60 seconds — listen for any exhaust leak
9. Verify cooling water flow through the new injection point — observe steam from the rear exhaust outlet
10. Bring the engine to 3000 RPM briefly — confirm new exhaust note
11. Scan with BUDS or compatible OBD diagnostic — no new fault codes
12. After shutdown, visually inspect the J-pipe delete adapter for any sealant migration

If clean: install complete.

Post-Install

Break-In

First water test should run a conservative throttle profile for the first 5 minutes. Sealant cures fully under operating temperature on the first heat cycle. After 5 minutes at part throttle, full throttle pulls are safe.

The exhaust note will be louder than stock. The 2021+ RXP-X hull resonates around 4800-5200 RPM with this kit (slightly higher than 2016-19) — hull buzz at that range is normal hull acoustics, not a fault.

Tuning

This kit is mechanical-only at the stock 300HP calibration. No ECU tune required for fitment. Stage 2 / Stage 3 tunes fully utilize the reduced backpressure.

For full Stage 3 systems on the 2021+ RXP-X, pair with:

• GT40-SD-INT-CF cold air intake
• GT40-SD-TUBE-230300-BOV charge tubing
• GT40-SD-OLC-300 open loop cooling (mandatory above 280 HP)
• Stage 3 calibration via Magic Module or equivalent

Service

• Inspect the J-pipe delete adapter every 25 run hours for any sealant weep
• Re-torque the 6 M10 SHCS at the first 10-hour service to 42 Nm
• Inspect the stainless outlet annually for any galvanic corrosion at the through-hull contact
• Inspect the cooling water injection hose every 25 hours
• After 200 hours, plan a full exhaust sealant inspection
• 2024+ hull zip-tie bracket support: replace zip tie every 100 hours (UV degradation)

Troubleshooting

| Symptom | Likely Cause | Fix |

|---|---|---|

| Sharp ticking at manifold-to-adapter joint | Gasket failure | Stop, drain, replace gasket + sealant, reinstall |

| Stainless outlet doesn't seat in through-hull | Wrong year kit OR adapter off-axis angle reversed | Verify hull year, recheck Step 5 adapter orientation |

| Exhaust gas smell in engine bay | J-pipe delete adapter leak | Retorque to 42 Nm, monitor, re-seal if persists |

| Steam in engine bay after run | Cooling water injection hose failure | Inspect, replace hose, retorque clamps |

| Engine performance unchanged | No supporting tune | Pair with Stage 2 / Stage 3 calibration for measurable gain |

| Loud resonance around 4800-5200 RPM | Normal 2021+ hull acoustics | Not a fault — hull resonates at this RPM with the new exhaust |

| Inner side panel won't reseat | Cable harness routed in front of panel | Reroute harness to behind panel before reinstall |

If symptoms persist after the checks above, contact GT40 Marine support before further operation.

Torque Reference Summary

| Fastener | Torque |

|---|---|

| J-pipe delete adapter to manifold M10 SHCS (all 6) | 42 Nm / 31 ft-lb |

| Stainless outlet V-band clamp | 22 Nm / 16 ft-lb |

| Cooling water injection #12 hose clamps | 3 Nm / 27 in-lb (snug, no hose-wall cut) |

| Port-side inner panel T25 Torx screws | 2.5 Nm / 22 in-lb |

| Battery negative terminal | 10 Nm / 89 in-lb |

All torque values nominal — refer to current Sea-Doo factory service manual for any conflicting OEM specifications.

Warranty

GT40 Marine warrants this kit free from defects in materials and workmanship for ninety (90) days from date of purchase. Warranty covers replacement of defective GT40-supplied components. Warranty does not cover:

• Damage from improper installation
• Damage from installation on wrong hull year (2016-19 or 2020 RXP-X — those need their respective kits)
• Damage from installation on RXP-X 325 (different exhaust geometry)
• Damage from premature engine start before full sealant cure
• Damage from operation without proper cooling water flow through the new injection point
• Damage to stainless components from galvanic corrosion in saltwater without sacrificial anode protection
• Use on craft outside the listed fitment matrix

To submit a warranty claim: email support@gt40marine.com with order number, photographs of the installed kit, the hull HIN, and a description of the failure mode. Response within two business days.

Support

• Email: support@gt40marine.com
• Site: gt40marine.com
• Install help: include the GT40 SKU above, hull HIN, and hull year in any support correspondence (hull year is critical for this kit)

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This guide is © 2026 GT40 Marine. All rights reserved.