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

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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.

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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.

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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)

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Safety

Read in full before starting.

1. Battery disconnected for the duration of the install.
2. Cold engine only. Exhaust components retain heat for over an hour after operation. The factory J-pipe runs at over 700°F.
3. Eye protection mandatory when working around the exhaust manifold — sharp edges, carbon deposits.
4. Hand protection. Marine exhaust has sharp flange edges. Cuts on contaminated metal are slow to heal.
5. No smoking / open flame. Exhaust sealant fumes are flammable until cured.
6. 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.

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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

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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:

1. 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)
2. Loosen the J-pipe-to-manifold V-band clamp (13 mm)
3. Loosen the J-pipe-to-waterbox V-band clamp (13 mm)
4. Lift the J-pipe out — heavy, ~8 lbs
5. Disconnect the waterbox inlet/outlet
6. Lift the waterbox out — bulky, plan a clear path
7. 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

1. Wipe the manifold outlet flange clean with shop towels
2. Inspect the gasket surface — must be flat, no carbon scoring, no warping
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

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.

1. Apply marine anti-seize compound to all 6 M10 × 35 mm SHCS threads
2. Position the supplied stainless gasket on the manifold flange, aligning the bolt holes
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, aligning the 6 bolt holes
5. Thread all 6 M10 SHCS through the adapter with flat washers — hand-tight only initially
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 — first pass at 22 Nm, second pass at 42 Nm
8. 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.

1. Apply marine anti-seize to the titanium 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 titanium outlet end must enter the through-hull fitting straight, no side load
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

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.

1. Locate the cooling water source on the engine block (typically a 3/8" NPT port near the rear of the head)
2. Locate the GT40 adapter's water injection port (visible boss on the upper 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 the hose routing avoids contact with the hot exhaust adapter — minimum 25 mm clearance to any exhaust surface
8. 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:

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. Replace the engine bay hatch, storage bin, seat
5. Connect the engine cooling flush hose
6. Start the engine on the trailer
7. Idle for 60 seconds — listen for any exhaust leak (sharp ticking, sustained whistling)
8. Verify cooling water flow through the new injection point — open the engine bay briefly during idle and confirm steam from the rear exhaust outlet
9. 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
10. Scan with BUDS or compatible OBD diagnostic — no new fault codes
11. After shutdown, visually inspect the J-pipe delete adapter for any sealant migration or weeping

If clean: install complete.

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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

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Troubleshooting

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

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Torque Reference Summary

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

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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.

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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.

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