TD performance guide for 998 turbo snowmobiles
High Performance 998 Turbo Technical Bulletin
Version 1.0 — Check back for updates and additions
Last Updated: [INSERT DATE]
This technical bulletin from Turbo Dynamics provides the verifications and testing procedures necessary to achieve maximum performance and optimal results from your high-performance 998cc Yamaha turbo-based snowmobile.
Table of Contents
- Rule #1: Always Use Fresh Fuel
- Engine Performance Specifications
- Critical Verification Checklist
- Big Turbo Requirement
- Chassis Preparation for High Performance
- Clutching
- TD Flasher / Copitrail Technical Notes
- Wastegate Installation Guide
- Wastegate Upgrade Warnings
- Engine Torque Specifications
- Quick Reference Card
- Contact Information
⚠️ Rule #1: Always Use Fresh Fuel
Drain old fuel and replace with fresh fuel before each session. If filling up at a gas station, pump 5 liters into your truck or car first to flush any 87 octane remaining in the pump's line and filter, then fill your canisters with fresh fuel.
Engine Performance Specifications
Spark Plug Gap Settings
| Application | Gap Setting |
|---|---|
| Trail use | .020 |
| Boost levels above 25 psi | .017 |
Optimal Steady RPM Targets
| Tune Type | Target RPM |
|---|---|
| Pump gas tunes | 9000 RPM (±100 RPM) |
| 1100T | 8000 RPM |
| Race tune (high boost) | 8400–8600 RPM |
| Professional racers | Custom settings may be required |
Head Gasket Upgrade
The TD head gasket upgrade (with head studs) is recommended for power levels of 340HP and above.
Best Value Power Upgrades (In Order)
| # | Upgrade |
|---|---|
| 1 | Tune + Clutch weights (Max spool 16) |
| 2 | TD dash reflash / multimap |
| 3 | Aftermarket exhaust, header, intake, and stage 6 kit |
Critical Verification Checklist
1. Verify All Clamps
Inspect all clamps including intercooler tubes, throttle body assembly, intake box, oil lines, and coolant lines. Loose clamps are extremely common.
Throttle Body Clamps: These are especially difficult to spot. Removal of the plastic intake is required for proper inspection of the clamps connecting the throttle body to the engine. These can pop off while the sled still appears to run well, but will result in significant power loss due to boost pressure leaks. The higher the boost, the more critical this inspection becomes.
? Pro Tip: For additional clamping pressure, shave 1/8" off the two aluminum tube spacers on the throttle body holding assembly.
Boost Leak Testing Procedure
| Step | Procedure |
|---|---|
| 1 | Use a boost leak tester with a compressor and air pressure regulator set to 20 psi |
| 2 | Connect the tester at the compressor outlet of the turbocharger using a high-flow fitting |
| 3 | Rotate the motor counterclockwise to close the valve and find the point where it holds pressure |
| 4 | A helper is useful for holding the primary clutch while pressurizing the intake |
| 5 | This test identifies boost leaks from damaged charge tubes, loose clamps, or weak BOV |
2. Never Spin Motor Clockwise
⚠️ WARNING: When looking at the clutch, always spin the motor counterclockwise only. Spinning clockwise can cause the motor to skip timing on the chain/sprocket.
3. Yamaha Clutch Torque (Yamaha Only)
| Step | Torque Procedure |
|---|---|
| 1 | Torque factory clutch to 110 ft-lbs |
| 2 | Back off the bolt |
| 3 | Finish at 60 ft-lbs |
4. Eliminate All Exhaust Leaks
Exhaust leaks—especially pre-turbo—significantly reduce power and spool-up performance.
Aftermarket Header Installation Tips
| Checkpoint | Details |
|---|---|
| Before Closing Up | Start the sled and verify there are no air leaks while the header is still cool |
| Physical Check | Place your hand near the exhaust flange and V-band to feel for airflow |
| Audio Check | Listen for unusual sounds that indicate leaks |
| V-Band Clamps | Commonly installed incorrectly—check for zero gap between the flanges |
5. Fuel System Upgrades (Required Above 300HP)
⚠️ REQUIRED: Any power output over 300HP requires a fuel pump upgrade and a 3 bar or 4 bar map sensor.
After Upgrading the Fuel Pump
| Component | Action Required |
|---|---|
| Red plastic 90° return fitting | Drill out the restrictor within to match the ID of the fitting |
| Black return fitting | No modification required |
| Pressure outlet to sending unit cap | Verify no leaks (test visually with adequate ventilation and no spark sources) |
| Suction pucks | Ensure they sit flat at the bottom of the tank at the proper angle like factory |
| Fuel pump suction filter | Confirm it sits flat on the bottom of the sending unit |
Fuel Pressure Settings
| Configuration | Pressure (Key On) |
|---|---|
| Stock fuel pressure | 43 psi |
| Most header tunes | 47 psi |
Recommendations
| Item | Purpose |
|---|---|
| Adjustable fuel pressure regulator | Monitor fuel pressure |
| Wideband O2 sensor module | Monitor proper operation and verify successful installation |
| Closed loop option | Automatic fuel adjustments via ECU and O2 sensor |
6. Aftermarket Wastegate Upgrade (New for 2020–2021 Season)
Wastegate Spring & Crack Pressure Settings
| Turbo Configuration | Spring | Crack Pressure |
|---|---|---|
| Stock Turbo | 11 psi spring | 11 psi (verification mandatory) |
| Big Turbo | 14 psi spring | 12–13 psi |
Setting Crack Pressure
Use a MityVac pressure tester or similar device to pressurize the top nipple of the aftermarket wastegate after installation on the turbocharger. Crack pressure is the pressure required to begin moving the wastegate arm.
⚠️ IMPORTANT: We will not send tunes to customers who have not tested crack pressure. If crack pressure is too high, it will result in unwanted overboost conditions and inconsistent boost control.
✓ Performance Note: The new wastegate upgrade tunes deliver game-changing performance with quicker spool and higher boost levels on Max20 and higher maps.
For detailed wastegate installation instructions, see the Wastegate Installation Guide section below.
⚠️ Big Turbo Requirement
For big turbo chargers and any sled running over 30 psi of boost, a 4 bar map sensor upgrade is mandatory.
Chassis Preparation for High Performance
Track Tension
Maintain a tight track—it must not hang at all when lifted off the ground and should be difficult to push off the front bogey wheel.
| Issue | Consequence |
|---|---|
| 4-wheel kit upgrade | Highly preferable for maintaining reliable track tension, especially at high power or high speeds |
| Loose track | Causes significant top speed loss as centrifugal forces cause it to balloon |
| Loose track (continued) | Can cause ratcheting of track drivers, damaging both the drivers and track |
| Radar running | Requires a very tight track due to expansion at high speeds |
Billet Track Adjusters
Highly recommended for models using thin cast aluminum adjusters. Factory cast adjusters can crack, leading to loss of track tension.
Managing Ski Lift
If you experience excessive ski lift during acceleration, tighten the limiter straps located at the front of the skid.
| Consideration | Details |
|---|---|
| Optimal acceleration | Sled lifting just an inch off the ground or maintaining light ski pressure |
| Wheelies | Feel fast but aren't fast |
| Over-tightening limiters | Reduces traction and slows the sled |
| Best approach | Find the best compromise for your setup |
Stud Length Recommendations
| Application | Stud Length | Quantity | Notes |
|---|---|---|---|
| Trail Riding | 1.45"–1.6" | 96–144 | For 1"–1.25" track lug height; 1.6" studs require tunnel protectors (STM) |
| Drag Racing (660–1000 ft) | 1.6"–1.8" | 144–192 | Short distance snow |
| Radar Running (2000+ ft) | 1.35"–1.45" | 96 | Long distance |
Gearing Recommendations
| Target Speed (GPS) | Gearing |
|---|---|
| Up to 123 MPH | 24/50 or 21/41 |
| 130 MPH | 21/38 |
| 135 MPH | 21/37 |
| 140 MPH | 22/37 |
? Pro Tip: If you want to make a number, put a lighter rider on it!
Clutching
Critical RPM Guidelines
⚠️ WARNING: Do not bang on the rev limiter or under-rev on pump gas. The sled must run 8500 RPM or higher on pump gas and must not hit the limiter at 9600 RPM.
Yamaha Clutches
| Specification | Details |
|---|---|
| Power Rating | Work well up to approximately 320HP (can handle more but less efficiently than aftermarket) |
| Primary Clutch | Dalton weights recommended (see separate chart for specifications) |
| Secondary Clutch | Our clutch kit provides better backshift and RPM control |
| Secondary Rollers | Heavy-duty rollers recommended |
Cat Clutches
| Specification | Details |
|---|---|
| Power Rating | Work adequately up to 320HP |
| Recommendation | Aftermarket clutches provide a significant upgrade on Cats |
| Weights | Dalton weights recommended with the Tornado clutch kit for secondary |
Aftermarket Clutch Options
| Clutch | Best For | Notes |
|---|---|---|
| STM 3VL | Limited trail use, drag racing/radar | Most of our records were set with this clutch or stock Yamaha clutches with weights |
| Tapp | Trail and racing use | New clutch this year, known for quiet operation and durability |
TD Flasher / Copitrail Technical Notes
Firmware
| Topic | Details |
|---|---|
| Updates | Firmware is constantly evolving with many new features this year, including closed loop adjustment fine tuning for advanced customers |
| Version | Use the latest release firmware unless otherwise specified |
| Special Firmware | Available for racers and tuners |
Flashing Procedure Tips
| # | Tip |
|---|---|
| 1 | When performing a "DASH" reflash, first completely unplug the Wideband O2 module from the harness |
| 2 | Update to the latest Gap flasher App (App Store) or Copitrail app (Apple Store) |
| 3 | Racing tip: If everything is working well with the sled and app, don't make changes at the last minute |
Turbosmart Wastegate Installation Guide
For Stock Turbo and Big Turbo Owners
Prerequisites for Wastegate Upgrade Tunes
To be eligible for wastegate upgrade tunes, you must be mechanically inclined—this modification is more complex than most others.
| Requirement | Purpose |
|---|---|
| Vacuum line routing | Careful attention required |
| Crack pressure setting | Precise setting on the wastegate required |
| TD flasher | With datalogging capabilities |
| Closed loop option | For proper verification and monitoring |
These are our flagship tunes, and we want them to represent us well while keeping you safe. Wastegate upgrade tunes provide significant advantages for big setups with headers, race fuel applications, and those wanting maximum ECU control over boost (new boost timer feature).
Installation Steps
| Step | Procedure |
|---|---|
| 1 | Remove and drill the factory restrictor/nipple located on the compressor outlet of the factory turbo |
| 2 | Reinsert the factory nipple into the housing |
| 3 | Block off the smaller nipple |
| 4 | Connect the larger nipple to the new dual-port solenoid we provide |
⚠️ MANDATORY: This configuration ensures proper boost control and is mandatory. New TD ECU tunes are required to run this wastegate upgrade.
⚠️ CAUTION: Follow the diagram below for proper vacuum line routing. Pay careful attention—improper routing can cause dangerous overboost or underboost conditions.
⚠️ TD Wastegate Upgrade Tunes: Technical Notes & Warnings
Congratulations! You now have the meanest, quickest-spooling tunes on the market. With these tunes:
| ✓ Benefit |
|---|
| You no longer need a wastegate locker to achieve 30 psi of boost on the race map |
| You can make full boost on the Max spool 20 tune when combined with a header (previously Max 20 with header only achieved 17–18 psi with the stock wastegate) |
Important Warnings
First Run Procedure
| Step | Critical Action |
|---|---|
| 1 | Be extremely careful on your first run |
| 2 | Keep an eye on boost levels |
| 3 | Only apply full throttle for 1 second initially |
| 4 | Check the log for potential overboost before continuing |
⚠️ DANGER: If vacuum lines aren't installed properly, it can create a FULL boost situation on all tunes. Refer to the diagram above for correct installation.
Octane Requirements
| Tune / Setup | Min Octane | Max Boost | Notes |
|---|---|---|---|
| Max20 with WG upgrade | 96 | 20–21 psi | Previously 17–18 psi without WG upgrade |
| Pure 91 octane | 91 | 20 psi max | Must be fresh fuel; you are near the limit |
| 93–94 octane | 93–94 | 23 psi | Generally works fine |
Boost Timer Tunes
Wastegate tunes with "BT" in the name are boost timer ready and have higher boost limiters. Exercise caution when adding boost via the boost timer.
| Tune | Boost Cut Threshold | Notes |
|---|---|---|
| Max 17 / Max 20 | Up to 28 psi before boost cut kicks in | — |
| Higher boost levels | — | Use Race maps with race fuel only |
? Overboost Emergency Contact
If you experience an overboost condition:
| Max 17 running 20+ psi | OVERBOOST |
| Max 20 running 22+ psi | OVERBOOST |
Call us immediately at 1-800-549-0246
Engine Torque Specifications (With Head Studs)
Quick Reference Card
| At-a-Glance Specifications | |
|---|---|
| Plug Gap (Trail) | .020 |
| Plug Gap (25+ psi) | .017 |
| Pump Gas RPM Target | 9000 RPM (±100) |
| Race Tune RPM Target | 8400–8600 RPM |
| Stock Fuel Pressure | 43 psi (key on) |
| Header Tune Fuel Pressure | 47 psi (key on) |
| Fuel Pump Upgrade Required | 300+ HP |
| Head Gasket Upgrade Required | 340+ HP |
| 4 Bar MAP Sensor Required | 30+ psi or Big Turbo |
| WG Crack Pressure (Stock Turbo) | 11 psi (11 psi spring) |
| WG Crack Pressure (Big Turbo) | 12–13 psi (14 psi spring) |
| Yamaha Clutch Torque | 110 ft-lbs → back off → 60 ft-lbs |
| Max Boost on 91 Octane | 20 psi |
| Max Boost on 93-94 Octane | 23 psi |
Contact Information
| Turbo Dynamics Contact Details | |
|---|---|
| Company | Turbo Dynamics |
| Address | 947 Route 148 Lochaber-Partie-Ouest, QC Canada J0X 3B0 |
| Phone (Emergency/Overboost) | 1-800-549-0246 |
| service@turbodynamics.ca | |
Document Version: 1.0
Check back regularly for updates and additions.