Stage 3 Dual Rear Exhaust Kit — Install Guide

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

Before You Start — Single vs Dual Decision

The Stage 3 Dual Rear Exhaust is a sibling kit to the Stage 3 Single Rear Exhaust (GT40-SD-EXH-ST3). They share base tooling and the same J-pipe delete adapter, but use different exit geometry.

| Feature | ST3 Single Rear | ST3 Dual Rear (this kit) |

---	---	---
Hull modification	One through-hull cut	Two through-hull cuts
Install time	3 hours	5 hours
Visual character	Performance-aggressive single tip	Symmetrical sports-touring dual tip
Sound character	Stronger center-channel note	Wider stereo spread
Cost	Lower	Higher (more material + labor)
Best for	RXT-X / RXP-X performance builds	GTX Limited touring builds
Recommended pairing	Stage 2 / Stage 3 single-engine	Stage 2 / Stage 3 builds where visual symmetry matters

If you're uncertain which to install: the single is more cost-effective and performs identically at the powertrain level. The dual is primarily an aesthetic choice for symmetrical hull silhouette.

Fitment

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

Not for: RXP-X (uses different hull rear geometry — single-rear-only). Not for Wake Pro 230 (the dual-cut hull modification interferes with the ski tow ring on Wake Pro). Confirm hull type before install.

In the Box

(1) GT40 titanium left rear exhaust outlet, hand-formed, brushed finish
(1) GT40 titanium right rear exhaust outlet, hand-formed, brushed finish
(1) GT40 dual-exit J-pipe delete adapter, billet aluminum, anodized black (has 2 exit ports vs 1 on the single-rear kit)
(1) Stainless steel exhaust gasket, fire-rated, marine-grade
(1) Water-injection adapter (for cooling water reintroduction post-J-pipe)
(2) Stainless V-band clamps, 2.5" ID (one per outlet)
(8 ft) High-temperature silicone water hose, 3/4" ID
(6) Stainless worm-gear hose clamps, #12
(6) M10 × 35 mm SHCS — manifold mounting (high tensile, marine-grade)
(6) M10 stainless flat washers
(1) Dual-hull transom template, paper, for marking the two through-hull cut locations symmetrically
(1) Hardware bag — spare gasket, spare V-band 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

All tools required for GT40-SD-EXH-ST3 (single rear) — see that guide's Tools Required section. Additionally:

2-3/4" hole saw (for the through-hull cuts — required because dual hulls need precise placement)
Hole saw arbor and pilot drill bit
Center punch
Painter's tape (for transom template positioning)
Eye protection AND respirator (fiberglass dust, MANDATORY)

Safety

All safety items in the GT40-SD-EXH-ST3 guide apply. Additionally:

Two through-hull cuts required. Each cut is a permanent hull modification. Measure twice, cut once — verify template placement is correct BEFORE either hole saw plunge.
Respirator MANDATORY during cuts. Fiberglass dust is a chronic respiratory hazard.
Symmetry matters. Asymmetric cuts will create a visibly off-center exhaust silhouette — there is no cosmetic recovery from an off-center cut.

Pre-Install Checklist

[ ] Watercraft on stable trailer or stand
[ ] Hull type confirmed as supported (RXT-X 300/325 or GTX Limited 300/325)
[ ] Battery negative disconnected and isolated
[ ] Engine bay clean and dry
[ ] Factory J-pipe + waterbox routing photographed
[ ] Ribbon delete already installed (Stage 3 dual assumes ribbon is removed)
[ ] Dual-hull transom template laid out and verified — the template uses centerline + bottom-edge alignment to place both cuts symmetrically
[ ] Marine-grade anti-seize ready
[ ] 5 hours minimum for install + 24 hours sealant cure before first water test

Step-by-Step Install

Step 1 — Access the Engine Bay

Same as GT40-SD-EXH-ST3 Step 1.

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

Same as GT40-SD-EXH-ST3 Step 2.

Step 3 — Inspect and Clean the Manifold Outlet Flange

Same as GT40-SD-EXH-ST3 Step 3.

Step 4 — Mark and Cut the Two Through-Hull Locations

This step REPLACES GT40-SD-EXH-ST3 Step 4 (which cut one hole).

Position the dual-hull transom template on the rear hull
The template references the existing single-rear factory through-hull location AND the centerline of the transom
Tape the template in place with painter's tape — do NOT let it shift
Mark the centers of BOTH 2-3/4" cut locations with the center punch
Remove the template
Verify the punch marks are equidistant from the centerline (within 5 mm) — if not, re-do the template positioning before cutting
Cut the LEFT hole first (working starboard-to-port reduces fiberglass dust spread):

Pilot drill through the marked center
2-3/4" hole saw at 300-500 RPM
Deburr the cut edge

Vacuum all fiberglass dust before the second cut
Cut the RIGHT hole:

Pilot drill through the marked center
2-3/4" hole saw
Deburr the cut edge

Inspect both cuts — must be uniformly round, no chips, equidistant from centerline
Vacuum all dust thoroughly

Step 5 — Install the GT40 Dual-Exit J-Pipe Delete Adapter

Same procedure as GT40-SD-EXH-ST3 Step 4 but with the dual-exit adapter:

Apply marine anti-seize to all 6 M10 × 35 mm SHCS threads
Position the supplied stainless gasket on the manifold flange
Apply a thin even bead of high-temperature exhaust sealant
Position the GT40 dual-exit adapter against the gasket — the adapter has TWO exit ports that will face the two cut holes
Thread all 6 M10 SHCS with flat washers
Snug, then torque to 42 Nm (31 ft-lb) in a star pattern across two passes
Wipe sealant squeeze-out

Step 6 — Install Both Titanium Rear Exhaust Outlets

This step REPLACES GT40-SD-EXH-ST3 Step 5 (which installed one outlet).

Apply marine anti-seize to the LEFT titanium outlet's mounting flange threads
Position the LEFT outlet against the dual-exit adapter's left exit flange
Slide the supplied V-band clamp around both flange edges
Snug the V-band clamp finger-tight
Rotate the outlet to align with the LEFT through-hull cut — outlet must enter the through-hull cleanly with no side load
Once aligned, torque the V-band clamp to 22 Nm (16 ft-lb) in two passes
Repeat all of the above for the RIGHT outlet on the right exit flange
Verify both outlets exit the hull symmetrically — visually inspect from outside the hull. If asymmetric (one outlet sits higher/lower than the other by more than 5 mm), re-check the V-band torque sequence and rotate the affected outlet

Step 7 — Reintroduce Cooling Water Injection

Same as GT40-SD-EXH-ST3 Step 6. The dual-exit adapter has one water injection port (not two) — cooling water reintroduction routing is identical to the single-rear kit.

Step 8 — Allow Sealant Cure Time

Same as GT40-SD-EXH-ST3 Step 7. 24-hour cure recommended because the dual-exit adapter has more sealed surface area than the single-rear adapter — longer cure is justified.

Step 9 — Reassembly and First Start

Same as GT40-SD-EXH-ST3 Step 8.

If clean: install complete.

Post-Install

Break-In

First water test should run a conservative throttle profile for the first 10 minutes (longer than the single-rear kit because two outlets generate slightly different airflow patterns at low RPM). After 10 minutes at part throttle, full throttle pulls are safe.

The dual-exit exhaust note has wider stereo spread than the single-rear. Some Standard 300HP hulls produce a noticeable left-right pulse at idle — this is normal for a dual exit and is not a fault.

Tuning

Same as GT40-SD-EXH-ST3. No ECU tune required for fitment. Stage 3 / Stage 4 tune fully utilizes the reduced backpressure.

Service

Inspect BOTH V-band clamps every 25 run hours — retorque to 22 Nm if any looseness
Re-torque the 6 M10 adapter SHCS at the first 10-hour service to 42 Nm
Inspect both titanium outlets annually for any corrosion at the through-hull contact point
Inspect the cooling water injection hose every 25 hours
After 200 hours, plan a full exhaust sealant inspection

Troubleshooting

| Symptom | Likely Cause | Fix |

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

| Asymmetric outlet silhouette | V-band torque uneven between left and right | Recheck V-band torque, rotate outlets to symmetric position, re-torque |

| One outlet leaks at the V-band | V-band damaged on the affected side | Replace V-band clamp on that side (kit includes one spare) |

| Engine performance below expectation | Dual outlets reduce backpressure too aggressively for stock tune | Stage 3 dual rear assumes a Stage 3 tune — pair with matched calibration |

| Sharp ticking sound | Gasket failure at adapter-manifold interface | Drain, replace gasket + sealant, reinstall |

| Steam from only one outlet | Cooling water injection routing uneven | Re-verify the single water-injection port routes correctly |

| Left-right pulse at idle | Normal dual-exit acoustics | Not a fault — dual exits naturally produce wider stereo character |

All other troubleshooting items in the GT40-SD-EXH-ST3 guide apply.

Torque Reference Summary

| Fastener | Torque |

|---|---|

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

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

| RIGHT 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 (particularly asymmetric through-hull cuts — these are NOT recoverable cosmetically)
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 (notably: not for RXP-X or Wake Pro)

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.

Connects to

GT40-SD-EXH-ST3_STAGE3_EXHAUST_INSTALL_GUIDE.md — sibling single-rear kit; many steps reference the single-rear guide for procedure
GT40-SD-RDK-SD300_RIBBON_DELETE_KIT_INSTALL_GUIDE.md — prerequisite ribbon delete
GT40-SD-EXH-OUTLET_REAR_EXHAUST_OUTLET_INSTALL_GUIDE.md — through-hull outlet procedure (also referenced for the dual-cut hull work)

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.