Stage 3 Single Rear Exhaust Kit — Install Guide

GT40 Marine | SKU GT40-SD-EXH-ST3 | Titanium Single Rear Exhaust + J-Pipe Delete | Rev 1.0 — 2026-05-24

Fitment

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

Not for: RXP-X (different hull geometry — use GT40-SD-EXH-RXPX300-1619 for 16-19 RXP-X 300, GT40-SD-EXH-RXPX325 family for 24+ RXP-X 325). Not for Spark or 1503 4-TEC. Confirm hull type and engine code before install. This is a Stage 3 component — it is designed to work with supporting modifications (open loop cooling, free-flow intake, supporting tune). Install on a stock craft will work but underutilize the kit's capacity.

In the Box

(1) GT40 titanium rear exhaust outlet, hand-formed, brushed finish
(1) GT40 J-pipe delete adapter, billet aluminum, anodized black
(1) Stainless steel exhaust gasket, fire-rated, marine-grade
(1) Water-injection adapter (for cooling water reintroduction post-J-pipe)
(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, water-injection check valve
(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 rear-mount fasteners sit deep in the hull)
Hose-clamp pliers
Marine-grade exhaust sealant applicator (small brush)
Flashlight or headlamp
Shop towels — exhaust will weep residual moisture
Anti-seize compound (marine-grade, copper-based)

Safety

Read in full before starting.

Battery disconnected for the duration of the install.
Cold engine only. Exhaust components retain heat for over an hour after operation. The factory J-pipe runs at over 700°F.
Eye protection mandatory when working around the exhaust manifold — sharp edges, carbon deposits.
Hand protection. Marine exhaust has sharp flange edges. Cuts on contaminated metal are slow to heal.
No smoking / open flame. Exhaust sealant fumes are flammable until cured.
Two-person lift recommended for the titanium outlet — although lightweight, the awkward geometry makes single-person positioning risky during install.

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
[ ] Battery negative disconnected and isolated
[ ] Engine bay clean and dry
[ ] Factory J-pipe + waterbox routing photographed before disassembly
[ ] Ribbon delete already installed (GT40-SD-RDK-SD300) — Stage 3 exhaust performance assumes ribbon is removed
[ ] Marine-grade anti-seize ready for application to all stainless fasteners
[ ] 2 hours minimum scheduled for the install + minimum 2 hours sealant cure before first start

Step-by-Step Install

Step 1 — Access the Engine Bay and Identify the J-Pipe

Remove the seat and engine bay top hatch. Lift the rear storage bin to expose the engine compartment.

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

Locate the factory J-pipe — the curved exhaust pipe running from the exhaust manifold outlet, around the rear of the engine bay, into the waterbox.

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

The factory rear exhaust system consists of:

The J-pipe (curves around the engine)
The waterbox (resonator chamber)
The rear exhaust outlet pipe and through-hull discharge fitting

Removal sequence:

Disconnect any cooling water injection lines feeding the J-pipe (typically 2 small hose connections at the top of the J-pipe — squeeze the spring clamps with pliers)
Loosen the J-pipe-to-manifold V-band clamp (13 mm)
Loosen the J-pipe-to-waterbox V-band clamp (13 mm)
Lift the J-pipe out — heavy, ~8 lbs
Disconnect the waterbox inlet/outlet
Lift the waterbox out — bulky, plan a clear path
Remove the through-hull rear exhaust outlet (this 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 — these are valuable resale parts.

Step 3 — Inspect and Clean the Manifold Outlet Flange

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

Step 4 — Install the GT40 J-Pipe Delete Adapter

The J-pipe delete adapter mounts directly to the manifold outlet flange, replacing the entire J-pipe + waterbox + rear-outlet section with a single component.

Apply marine anti-seize compound to all 6 M10 × 35 mm SHCS threads
Position the supplied stainless gasket on the manifold flange, aligning the bolt holes
Apply a thin even bead of high-temperature exhaust sealant around the gasket's outboard face
Position the GT40 J-pipe delete adapter against the gasket, aligning the 6 bolt holes
Thread all 6 M10 SHCS through the adapter with flat washers — hand-tight only initially
Confirm the adapter is square to the manifold (no rotational offset)
Torque the 6 bolts to 42 Nm (31 ft-lb) in a star pattern across two passes — first pass at 22 Nm, second pass at 42 Nm
Wipe any sealant squeeze-out with a clean rag

Step 5 — Install the Titanium Rear Exhaust Outlet

The titanium outlet connects the J-pipe delete adapter to the through-hull rear exhaust fitting.

Apply marine anti-seize to the titanium outlet's mounting flange threads
Position the outlet against the J-pipe delete adapter's exit flange
Thread the supplied V-band clamp around both flange edges
Snug the clamp finger-tight
Rotate the outlet to align with the through-hull exit point — the titanium outlet end must enter the through-hull fitting straight, no side load
Once aligned, torque the V-band clamp to 22 Nm (16 ft-lb) in two passes
Verify the outlet exits the hull cleanly — no contact with hull fiberglass at any point

Step 6 — Reintroduce Cooling Water Injection

The J-pipe delete removes the factory cooling water reintroduction at the J-pipe top. The replacement injection point sits in the GT40 adapter.

Locate the cooling water source on the engine block (typically a 3/8" NPT port near the rear of the head)
Locate the GT40 adapter's water injection port (visible boss on the upper face of the J-pipe delete adapter)
Cut the supplied silicone water hose to length from source to injection point
Slide #12 clamps onto each hose end
Push the hose onto the source fitting, then the adapter water-injection port
Tighten both clamps to 3 Nm (27 in-lb) equivalent
Verify the hose routing avoids contact with the hot exhaust adapter — minimum 25 mm clearance to any exhaust surface
Install the supplied check valve inline if not already present — prevents exhaust backflow into the water source if the engine ever runs without water

Step 7 — Allow Sealant Cure Time

The exhaust sealant requires a minimum of 2 hours cure time before engine start. Do not skip — premature start blows uncured sealant out of the joint and into the engine bay.

If you can wait overnight, recommended. Maximum cure strength at 24 hours.

Step 8 — Reassembly and First Start

After cure:

Walk the engine bay — every fastener, every clamp, every hose joint
Confirm no tools or hardware remaining
Reconnect the battery negative terminal — torque to 10 Nm (89 in-lb)
Replace the engine bay hatch, storage bin, seat
Connect the engine cooling flush hose
Start the engine on the trailer
Idle for 60 seconds — listen for any exhaust leak (sharp ticking, sustained whistling)
Verify cooling water flow through the new injection point — open the engine bay briefly during idle and confirm steam from the rear exhaust outlet
Bring the engine to 3000 RPM briefly — the new exhaust note will be significantly louder and more open than stock; this is the intended Stage 3 character
Scan with BUDS or compatible OBD diagnostic — no new fault codes
After shutdown, visually inspect the J-pipe delete adapter for any sealant migration or weeping

If clean: install complete.

Post-Install

Break-In

First water test should run a conservative throttle profile for the first 5 minutes — gradual ramp to half throttle. This allows the sealant to complete its final cure under full operating temperature. After 5 minutes at part throttle, full throttle pulls are safe.

The exhaust note will be dramatically louder than stock above 5000 RPM. This is the intended Stage 3 character. Some hulls may resonate noticeably at certain RPM — this is hull acoustics, not a fault of the kit.

Tuning

Stage 3 exhaust performance requires a Stage 3 tune to fully realize. On a stock tune, the kit reduces backpressure but the ECU will not adapt the fuel map to take advantage of the new flow profile. Expect 5-8 HP gain on a stock tune; expect 25-40 HP gain with a matched Stage 3 tune + supporting modifications.

For full Stage 3 systems, pair with:

GT40-SD-INT-CF cold air intake
GT40-SD-TUBE-230300-BOV or GT40-SD-TUBE-325-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 (initial gasket compression)
Inspect the titanium outlet annually for any corrosion at the through-hull contact point (titanium resists corrosion but galvanic activity can occur if dissimilar metals contact in saltwater)
Inspect the cooling water injection hose every 25 hours — replace if any cracking, swelling, or saturation softening
After 200 hours, plan a full exhaust sealant inspection

Troubleshooting

| Symptom | Likely Cause | Fix |

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

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

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

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

| Titanium outlet visibly discolored (rainbow) | Normal — heat-cycle bluing of titanium | Cosmetic only, no functional issue |

| Engine performance unchanged | No supporting tune | Stage 3 exhaust without matched tune yields only modest gains — pair with a Stage 3 calibration |

| Check Engine + P0420 catalyst code | Not applicable on PWC | Sea-Doo does not run catalytic converters; verify the code is real |

| Significant backpressure perceptible | Inlet partially obstructed | Inspect inside of the through-hull fitting for debris |

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 |

| Titanium 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) |

| 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 (including under-torqued fasteners)
Damage from premature engine start before full sealant cure
Damage from operation without proper cooling water flow through the new injection point
Damage to titanium components from galvanic corrosion in saltwater operation 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, 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 and your hull serial number in any support correspondence

Built in the United States. Designed for buyers who want the best.