Yamaha Intercooler Kit with Blow-Off Valve — Install Guide

GT40 Marine | SKU GT40-YAM-IC-1819L | Yamaha 1.8L SVHO/SHO Intercooler + BOV | Rev 1.0 — 2026-05-24

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Fitment — Yamaha 1.8L Supercharged

This intercooler kit fits the Yamaha 1.8L supercharged (SVHO + SHO) engine family. SHO-trim hulls were factory-equipped with a smaller intercooler than SVHO; this kit standardizes on the larger SVHO-equivalent geometry that supports Stage 2+ boost levels.

Not for: 1.9L (2024+) — Yamaha changed the intercooler architecture in the 1.9L revision; that platform requires a different kit. Not for naturally-aspirated HO trims (no boost = no intercooler needed). Not for 1503 4-TEC platforms. Confirm engine displacement (1.8L) AND trim (SVHO or SHO) before install.

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Before You Start — Decision Tree

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In the Box

• (1) GT40 high-capacity intercooler, aluminum, ceramic-coated
• (2) GT40-formed charge tubes (inlet + outlet)
• (1) Blow-off valve, billet, spring-actuated
• (1) BOV mounting flange, welded to outlet tube
• (4) Silicone couplers, reinforced charge-grade
• (8) T-bolt clamps, stainless
• (1) Vacuum reference line, 6 ft silicone, 4 mm ID
• (4) Spring vacuum-line clamps
• (4) M8 × 25 mm SHCS — intercooler mounting
• (4) M8 stainless flat washers
• (2) M6 × 25 mm SHCS — BOV-to-flange
• (1) Marine-grade thread sealant tube
• (1) Install hardware bag — spare couplers, spare clamps
• (1) GT40 product registration card
• (1) This guide

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Tools Required

• 8 mm / 10 mm / 13 mm sockets + ratchet
• T25 + T30 Torx drivers
• 4 mm + 5 mm + 6 mm hex keys
• 1/4" + 3/8" drive torque wrenches, 5–25 Nm range
• Hose-clamp pliers
• Marine-grade thread sealant applicator
• Flashlight or headlamp
• Shop towels — residual condensate from disconnected intercooler

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Safety

1. Battery disconnected for duration
2. Cold engine only — supercharger and intercooler reach significant temperature
3. Eye protection when disconnecting charge tubing — residual condensate sprays
4. Hand protection when handling ceramic-coated tubing
5. No smoking / open flame
6. Two-person lift recommended for intercooler positioning — bulky, awkward in tight engine bay

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Pre-Install Checklist

• [ ] Watercraft on stable trailer or stand
• [ ] Battery negative disconnected and isolated
• [ ] Engine bay clean and dry
• [ ] Stock intercooler + charge tubing routing photographed
• [ ] All 4 supplied silicone couplers matched to tube ends (varying ID)
• [ ] BOV pre-assembled to flange, hand-tight only

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Step-by-Step Install

Step 1 — Access the Engine Bay

Remove seat. Open engine bay top hatch. Disconnect battery negative terminal.

Step 2 — Remove the Stock Intercooler and Charge Tubing

The Yamaha 1.8L SHO/SVHO architecture uses:

• Inlet charge tube from supercharger outlet to intercooler inlet
• Stock intercooler mounted on engine bay sidewall
• Outlet charge tube from intercooler to throttle body

Removal:

1. Loosen all four clamps on inlet tube (supercharger end + intercooler inlet end)
2. Pull inlet tube free — catch residual condensate with shop towel
3. Loosen four clamps on outlet tube (intercooler outlet + throttle body end)
4. Pull outlet tube free
5. Disconnect coolant lines feeding the intercooler (Yamaha intercoolers are typically water-cooled — 2 hose connections, spring clamps)
6. Remove 4 M8 mounting fasteners
7. Lift intercooler out — ~6 lbs

Set stock components aside (retain if you may sell craft in stock form).

Step 3 — Install GT40 Intercooler

1. Position new GT40 intercooler against engine bay mounting bosses
2. Thread 4 M8 × 25 mm SHCS with flat washers
3. Snug evenly, torque to 18 Nm (13 ft-lb) in cross pattern, two passes
4. Reconnect water cooling lines to the intercooler (2 hose connections, spring clamps)

Step 4 — Pre-Fit and Install Charge Tubing

1. Slide T-bolt clamps + silicone couplers onto supercharger outlet
2. Insert GT40 inlet charge tube, ceramic-coated side outboard
3. Slide T-bolt clamps + couplers onto intercooler inlet
4. Lower inlet tube into position — coupler engagement 1/2 in. minimum each end
5. Rotate tube for clearance from throttle linkage + harness loom (10 mm minimum)
6. Repeat for outlet tube — intercooler outlet → throttle body, with BOV flange facing outboard

Step 5 — Torque Charge-Tube Clamps

Sequence: supercharger-end of inlet, intercooler-inlet end, intercooler-outlet end, throttle-body end. Torque each T-bolt clamp to 5 Nm (44 in-lb) alternating in two passes.

Pull-test each joint after torque.

Step 6 — Install BOV on Outlet Tube Flange

1. Position BOV body against the flange with supplied gasket
2. Thread 2 M6 × 25 mm SHCS through BOV into flange
3. Torque to 10 Nm (89 in-lb) with 5 mm hex socket
4. Confirm BOV outlet points outboard — discharge vents to engine bay, not into hull

Step 7 — Route Vacuum Reference Line

1. Locate factory MAP sensor port on intake manifold
2. Cut supplied 4 mm silicone line to length — direct route, no excess loop
3. Push ends onto BOV vacuum nipple and MAP port — secure with spring clamps
4. Verify line has no kinks, no contact with hot exhaust

Step 8 — Reassembly and First Start

1. Walk engine bay — every fastener, every clamp
2. Reconnect battery negative — torque to 10 Nm
3. Connect cooling flush hose
4. Start engine on trailer — idle 60 seconds, listen for boost leaks (lean stumble = leak)
5. Bring to 3000 RPM briefly — confirm BOV opens on throttle close
6. Scan with Yamaha YDS — no fault codes (P0238 indicates charge-side leak)

If clean: install complete.

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Post-Install

Break-In

First water test: conservative throttle for first 5 minutes — gradual ramp to half throttle, then full pulls. Ceramic coating completes first heat-cure cycle.

Tuning

Stage 2 tune is the matched calibration for this kit. Stock tune yields 5-8 HP; Stage 2 tune yields 15-25 HP gain when paired with intake + exhaust.

Service

• Inspect couplers + clamps every 25 hours — retorque if relaxed
• Inspect vacuum reference line every 50 hours
• Coolant flow check on the water-cooled intercooler annually
• Saltwater: rinse intercooler exterior with fresh water after every saltwater session

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Troubleshooting

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Torque Reference Summary

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Warranty

90-day GT40 warranty per the standard policy. Does not cover improper installation, boost above the BOV-rated ceiling (typically 18 psi for SVHO), saltwater corrosion without anode protection, or use outside fitment.

Claims: support@gt40marine.com.

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Support

• Email: support@gt40marine.com
• Site: gt40marine.com
• Install help: include SKU, hull HIN, trim (SVHO or SHO), and tune status in 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.