Yamaha Rear Exhaust Kit — Install Guide

GT40 Marine | SKU GT40-YAM-EXH-1819L | Yamaha 1.8L / 1.9L Free-Flow Rear Exhaust | Rev 1.0 — 2026-05-24

Fitment — Yamaha 1.8L / 1.9L

| Family | Models | Years |

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

| FX (SVHO / SHO / HO) | FX, FX Cruiser, FX Limited, FX HO, FX Cruiser HO | 2008-2026 |

| GP Performance | FZR, FZS, GP1800, GP1800R, GP | 2009-2026 |

| VX Touring | VX Cruiser HO, VX Limited HO, VXR, VXS | 2011-2026 |

Not for: 1.0L / 1.05L / 1.6L Yamaha engines, JetBlaster, standup hulls. Confirm engine displacement (1.8L or 1.9L).

Before You Start — Decision Tree

| # | Question | Branch |

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

| 1 | Engine 1.8L or 1.9L? | Continue |

| 2 | Running free-flow waterbox already? | Pairs strongly — gains compound. If not, recommend GT40-YAM-WB-1819L install first |

| 3 | Tune above stock? | Required for full gain on SVHO; HO trim gains on stock tune |

| 4 | Through-hull exhaust outlet already in place? | If new install, see Step 4 hull-cut procedure |

In the Box

(1) GT40 mandrel-bent stainless rear exhaust tube
(1) Through-hull stainless outlet flange
(1) Stainless V-band clamp, 2.5" ID
(1) High-temperature exhaust gasket, fire-rated
(3 ft) High-temperature silicone water injection hose, 3/4" ID
(2) #12 stainless hose clamps
(4) M8 × 25 mm SHCS — mounting hardware
(4) M8 stainless flat washers
(1) Marine-grade exhaust sealant tube
(1) Hardware bag — spare gasket, spare V-band
(1) GT40 product registration card
(1) This guide

Tools Required

10 mm / 13 mm sockets
T25 + T30 Torx drivers
5 mm + 6 mm hex keys
1/4" + 3/8" drive torque wrenches, 5–25 Nm range
2-3/4" hole saw + arbor (only if installing new through-hull outlet)
Hose-clamp pliers
Marine-grade exhaust sealant applicator
Flashlight or headlamp
Marine-grade copper anti-seize compound

Safety

Battery disconnected for duration
Cold engine only — Yamaha 1.8L/1.9L exhaust retains heat for over an hour
Eye protection mandatory
Respirator mandatory if cutting through-hull (fiberglass dust)
No smoking / open flame
Two-person lift recommended for stainless tube positioning on FX Cruiser hulls

Pre-Install Checklist

[ ] Watercraft on stable trailer
[ ] Engine 1.8L/1.9L confirmed
[ ] Battery negative disconnected
[ ] Factory exhaust routing photographed
[ ] Sealant cure time scheduled (2 hours minimum before first start)

Step-by-Step Install

Step 1 — Access the Engine Bay

Remove seat (two-person lift on FX Cruiser). Open engine bay top hatch. Disconnect battery negative.

Step 2 — Remove Factory Exhaust

Factory Yamaha rear exhaust connects from the waterbox outlet to the through-hull discharge fitting via a short tube.

Disconnect water injection line at the factory tube
Loosen the waterbox-to-rear-exhaust V-band clamp (13 mm)
Pull the factory exhaust tube free
Inspect the waterbox V-band groove + the through-hull approach for any damage

Step 3 — Inspect and Clean Mounting Surfaces

Wipe the waterbox V-band flange clean
Inspect for flatness and warping — surface must be uniform
Light scuff with 220-grit sandpaper if contaminated
Wipe with solvent, allow 60 seconds evaporation

Step 4 — Install Through-Hull Outlet (if new install)

Skip this step if a through-hull outlet is already in place.

Use the supplied transom template (or measure for symmetric placement on Yamaha hull)
Center-punch the cut location
Pilot drill, then 2-3/4" hole saw at 300-500 RPM
Deburr cut edge
Vacuum all fiberglass dust

Step 5 — Install GT40 Rear Exhaust Tube

Apply marine anti-seize to V-band clamp threads
Position stainless gasket on the waterbox outlet flange
Apply thin bead of exhaust sealant to outboard face of gasket
Position GT40 stainless tube against waterbox flange
Slide V-band clamp around joint, snug finger-tight
Rotate tube to align with through-hull exit — straight approach, no side load
Torque V-band to 22 Nm (16 ft-lb) in two passes

Step 6 — Install Through-Hull Outlet Flange

Apply marine sealant around the through-hull cut perimeter
Position the supplied outlet flange against the hull exterior
Thread 4 M8 × 25 mm SHCS through the flange + hull, with flat washers + lock nuts on interior side
Snug all 4 in a cross pattern
Wait 5 minutes for sealant skin-cure
Torque all 4 M8 to 8 Nm (71 in-lb) in star pattern — over-tightening causes hull distortion

Step 7 — Reconnect Cooling Water Injection

Cut supplied silicone hose to length
Slide #12 clamps onto each end
Push hose onto engine block water source + onto the new GT40 tube's water injection port
Tighten clamps to 3 Nm (27 in-lb)
Verify hose routing — minimum 25 mm clearance to hot exhaust components

Step 8 — Allow Sealant Cure

Minimum 2 hours cure time before engine start. 24 hours recommended for full strength. Saltwater exposure should not occur for 48 hours minimum.

Step 9 — First Start

After cure:

Walk engine bay — every fastener, every clamp
Reconnect battery negative — torque to 10 Nm
Connect cooling flush hose
Start engine on trailer — idle 60 seconds, listen for exhaust leaks
Verify water flow at through-hull outlet
Bring to 3000 RPM briefly — confirm new exhaust note (loud, free-flow)
Scan with Yamaha YDS — no new fault codes

If clean: install complete.

Post-Install

Break-In

First water test: conservative throttle for first 5 minutes — gradual ramp to half throttle. Sealant final cure happens during this period.

The Yamaha 1.8L/1.9L exhaust note will be substantially louder than stock. SVHO trim shows the most dramatic change. Some hulls resonate at specific RPM (typically 4500-5500) — normal hull acoustics, not a fault.

Tuning

Mechanical-only. No tune required. Stage 2 tune yields full gain when paired with intake + intercooler + waterbox.

Service

Inspect V-band joint every 25 hours
Re-torque V-band at 10-hour service to 22 Nm
Inspect through-hull seal annually for sealant migration
Annual freshwater flush of the exterior tube for saltwater operation
Replace silicone water injection hose every 3 seasons

Troubleshooting

| Symptom | Likely Cause | Fix |

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

| Sharp ticking at V-band | Gasket failure | Replace gasket + sealant, reinstall |

| Exhaust gas smell in bay | V-band leak | Retorque to 22 Nm, monitor |

| Water intrusion at through-hull | Sealant not cured | Trailer, allow 48 hr full cure, retorque M8 to 8 Nm |

| Steam in engine bay | Water injection hose failure | Inspect, replace, retighten clamps |

| Engine performance unchanged | No supporting modifications | Pair with intake + intercooler + tune for full gain |

| Hull resonance at 4500-5500 RPM | Normal acoustics | Not a fault |

Torque Reference Summary

| Fastener | Torque |

|---|---|

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

| Through-hull flange M8 SHCS (4) | 8 Nm / 71 in-lb |

| Water injection #12 clamps | 3 Nm / 27 in-lb |

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

Warranty

90-day GT40 warranty per standard policy. Does not cover improper hull cut, premature engine start before cure, operation without proper water flow, or use outside fitment.

Claims: support@gt40marine.com with order, photos, failure description.

Support

Email: support@gt40marine.com
Site: gt40marine.com
Install help: include SKU, hull HIN, trim, model year, and engine displacement in correspondence

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

Yamaha Rear Exhaust Kit — Install Guide

GT40 Marine | SKU GT40-YAM-EXH-1819L | Yamaha 1.8L / 1.9L Free-Flow Rear Exhaust | Rev 1.0 — 2026-05-24

Fitment — Yamaha 1.8L / 1.9L

| Family | Models | Years |

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

| FX (SVHO / SHO / HO) | FX, FX Cruiser, FX Limited, FX HO, FX Cruiser HO | 2008-2026 |

| GP Performance | FZR, FZS, GP1800, GP1800R, GP | 2009-2026 |

| VX Touring | VX Cruiser HO, VX Limited HO, VXR, VXS | 2011-2026 |

Not for: 1.0L / 1.05L / 1.6L Yamaha engines, JetBlaster, standup hulls. Confirm engine displacement (1.8L or 1.9L).

Before You Start — Decision Tree

| # | Question | Branch |

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

| 1 | Engine 1.8L or 1.9L? | Continue |

| 2 | Running free-flow waterbox already? | Pairs strongly — gains compound. If not, recommend GT40-YAM-WB-1819L install first |

| 3 | Tune above stock? | Required for full gain on SVHO; HO trim gains on stock tune |

| 4 | Through-hull exhaust outlet already in place? | If new install, see Step 4 hull-cut procedure |

In the Box

(1) GT40 mandrel-bent stainless rear exhaust tube
(1) Through-hull stainless outlet flange
(1) Stainless V-band clamp, 2.5" ID
(1) High-temperature exhaust gasket, fire-rated
(3 ft) High-temperature silicone water injection hose, 3/4" ID
(2) #12 stainless hose clamps
(4) M8 × 25 mm SHCS — mounting hardware
(4) M8 stainless flat washers
(1) Marine-grade exhaust sealant tube
(1) Hardware bag — spare gasket, spare V-band
(1) GT40 product registration card
(1) This guide

Tools Required

10 mm / 13 mm sockets
T25 + T30 Torx drivers
5 mm + 6 mm hex keys
1/4" + 3/8" drive torque wrenches, 5–25 Nm range
2-3/4" hole saw + arbor (only if installing new through-hull outlet)
Hose-clamp pliers
Marine-grade exhaust sealant applicator
Flashlight or headlamp
Marine-grade copper anti-seize compound

Safety

Battery disconnected for duration
Cold engine only — Yamaha 1.8L/1.9L exhaust retains heat for over an hour
Eye protection mandatory
Respirator mandatory if cutting through-hull (fiberglass dust)
No smoking / open flame
Two-person lift recommended for stainless tube positioning on FX Cruiser hulls

Pre-Install Checklist

[ ] Watercraft on stable trailer
[ ] Engine 1.8L/1.9L confirmed
[ ] Battery negative disconnected
[ ] Factory exhaust routing photographed
[ ] Sealant cure time scheduled (2 hours minimum before first start)

Step-by-Step Install

Step 1 — Access the Engine Bay

Remove seat (two-person lift on FX Cruiser). Open engine bay top hatch. Disconnect battery negative.

Step 2 — Remove Factory Exhaust

Factory Yamaha rear exhaust connects from the waterbox outlet to the through-hull discharge fitting via a short tube.

Disconnect water injection line at the factory tube
Loosen the waterbox-to-rear-exhaust V-band clamp (13 mm)
Pull the factory exhaust tube free
Inspect the waterbox V-band groove + the through-hull approach for any damage

Step 3 — Inspect and Clean Mounting Surfaces

Wipe the waterbox V-band flange clean
Inspect for flatness and warping — surface must be uniform
Light scuff with 220-grit sandpaper if contaminated
Wipe with solvent, allow 60 seconds evaporation

Step 4 — Install Through-Hull Outlet (if new install)

Skip this step if a through-hull outlet is already in place.

Use the supplied transom template (or measure for symmetric placement on Yamaha hull)
Center-punch the cut location
Pilot drill, then 2-3/4" hole saw at 300-500 RPM
Deburr cut edge
Vacuum all fiberglass dust

Step 5 — Install GT40 Rear Exhaust Tube

Apply marine anti-seize to V-band clamp threads
Position stainless gasket on the waterbox outlet flange
Apply thin bead of exhaust sealant to outboard face of gasket
Position GT40 stainless tube against waterbox flange
Slide V-band clamp around joint, snug finger-tight
Rotate tube to align with through-hull exit — straight approach, no side load
Torque V-band to 22 Nm (16 ft-lb) in two passes

Step 6 — Install Through-Hull Outlet Flange

Apply marine sealant around the through-hull cut perimeter
Position the supplied outlet flange against the hull exterior
Thread 4 M8 × 25 mm SHCS through the flange + hull, with flat washers + lock nuts on interior side
Snug all 4 in a cross pattern
Wait 5 minutes for sealant skin-cure
Torque all 4 M8 to 8 Nm (71 in-lb) in star pattern — over-tightening causes hull distortion

Step 7 — Reconnect Cooling Water Injection

Cut supplied silicone hose to length
Slide #12 clamps onto each end
Push hose onto engine block water source + onto the new GT40 tube's water injection port
Tighten clamps to 3 Nm (27 in-lb)
Verify hose routing — minimum 25 mm clearance to hot exhaust components

Step 8 — Allow Sealant Cure

Minimum 2 hours cure time before engine start. 24 hours recommended for full strength. Saltwater exposure should not occur for 48 hours minimum.

Step 9 — First Start

After cure:

Walk engine bay — every fastener, every clamp
Reconnect battery negative — torque to 10 Nm
Connect cooling flush hose
Start engine on trailer — idle 60 seconds, listen for exhaust leaks
Verify water flow at through-hull outlet
Bring to 3000 RPM briefly — confirm new exhaust note (loud, free-flow)
Scan with Yamaha YDS — no new fault codes

If clean: install complete.

Post-Install

Break-In

First water test: conservative throttle for first 5 minutes — gradual ramp to half throttle. Sealant final cure happens during this period.

Tuning

Mechanical-only. No tune required. Stage 2 tune yields full gain when paired with intake + intercooler + waterbox.

Service

Inspect V-band joint every 25 hours
Re-torque V-band at 10-hour service to 22 Nm
Inspect through-hull seal annually for sealant migration
Annual freshwater flush of the exterior tube for saltwater operation
Replace silicone water injection hose every 3 seasons

Troubleshooting

| Symptom | Likely Cause | Fix |

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

| Sharp ticking at V-band | Gasket failure | Replace gasket + sealant, reinstall |

| Exhaust gas smell in bay | V-band leak | Retorque to 22 Nm, monitor |

| Water intrusion at through-hull | Sealant not cured | Trailer, allow 48 hr full cure, retorque M8 to 8 Nm |

| Steam in engine bay | Water injection hose failure | Inspect, replace, retighten clamps |

| Engine performance unchanged | No supporting modifications | Pair with intake + intercooler + tune for full gain |

| Hull resonance at 4500-5500 RPM | Normal acoustics | Not a fault |

Torque Reference Summary

| Fastener | Torque |

|---|---|

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

| Through-hull flange M8 SHCS (4) | 8 Nm / 71 in-lb |

| Water injection #12 clamps | 3 Nm / 27 in-lb |

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

Warranty

90-day GT40 warranty per standard policy. Does not cover improper hull cut, premature engine start before cure, operation without proper water flow, or use outside fitment.

Claims: support@gt40marine.com with order, photos, failure description.

Support

Email: support@gt40marine.com
Site: gt40marine.com
Install help: include SKU, hull HIN, trim, model year, and engine displacement in correspondence

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