Product Description
The FTI Performance TH400-4K21 Level 4 Automatic Transmission Package is a heavy-duty GM Turbo 400 drivetrain assembly developed for specialized high-performance automotive applications requiring robust internal construction and a matched torque converter.
Rated for an advertised 900 horsepower, this transmission package combines an FTI Level 4 TH400 three-speed automatic transmission with a billet torque converter, integrated transbrake, performance transmission fluid, and a complete cooler package.
The TH400-4K21 is built around the traditional General Motors Turbo 400 transmission architecture, recognized for its durable three-speed automatic configuration and suitability for appropriately engineered performance drivetrains.
Unlike a conventional stock replacement transmission, the FTI Level 4 configuration incorporates upgraded transmission components intended to support the manufacturer’s increased power rating.
These components include a 34-element intermediate sprag, performance clutch packs, treated steel plates, high-flow transmission pump, billet forward clutch hub, reinforced intermediate retainer, and a heavy-duty transmission configuration.
Its full-manual valve body features a reverse shift pattern and an integrated transbrake, distinguishing it from conventional automatic transmissions intended for everyday passenger vehicle operation.
The included FTI SST89-0 billet torque converter features an advertised 3,400–3,800 RPM flash stall range, along with a mechanical diode and anti-ballooning plate construction.
The TH400-4K21 kit also includes 12 quarts of FTI performance automatic transmission fluid, a locking transmission dipstick and tube, and a complete cooling package consisting of a transmission cooler, approximately 15 feet of cooler line, fittings, and hose ends.
These supplied components make the package a comprehensive drivetrain assembly rather than a transmission-only product.
The Chevrolet bellhousing pattern and GM TH400 transmission configuration make it suitable for professionally evaluated Chevrolet-based drivetrain applications where the engine, converter, transmission, mounting system, and other related components are compatible.
The FTI Performance TH400-4K21 is intended for specialized vehicle builds evaluated and installed by qualified automotive professionals. Its performance characteristics and manual shift configuration make correct application selection essential.
Key Features
900HP Performance Rating
Advertised for engine applications producing up to 900 horsepower, subject to the manufacturer’s operating requirements.
Level 4 Performance Transmission
Features upgraded internal components designed for demanding performance applications.
GM Turbo 400 Architecture
Based on the durable GM TH400 three-speed automatic transmission platform.
FTI Billet Torque Converter Included
Supplied with an FTI SST89-0 billet torque converter matched to the package configuration.
3,400–3,800 RPM Advertised Stall Range
Includes a high-stall torque converter with a published flash stall range of 3,400–3,800 RPM.
Full-Manual Valve Body
Features a full-manual transmission valve body with reverse shift pattern.
Integrated Transbrake
Includes the manufacturer’s performance transbrake configuration.
34-Element Intermediate Sprag
Equipped with a reinforced intermediate sprag assembly.
Heavy-Duty Transmission Internals
Features upgraded friction clutches, steel plates, billet clutch components, and related heavy-duty parts.
Deep Aluminum Transmission Pan
Includes a deep aluminum pan as part of the performance transmission configuration.
Complete Cooling Package
Includes a transmission cooler, cooler lines, fittings, and related components.
Performance Transmission Fluid
Supplied with 12 quarts of FTI automatic transmission fluid.
Technical Specifications
| Specification | Details |
|---|---|
| Manufacturer | FTI Performance |
| Product Series | TH400 Level 4 |
| Manufacturer Part Number | TH400-4K21 |
| UPC | 887753824790 |
| Store SKU | FTI-TH400-4K21-L4-2191 |
| Product Category | Automatic Transmission Package |
| Transmission Model | GM TH400 / Turbo 400 |
| Performance Level | Level 4 |
| Advertised Horsepower Rating | 900 HP |
| Transmission Type | Automatic |
| Number of Forward Gears | 3 |
| First Gear Ratio | 2.48:1 (listed specifications vary slightly by source) |
| Second Gear Ratio | 1.48:1 |
| Third Gear Ratio | 1.00:1 |
| Overdrive | No |
| Valve Body | Full Manual |
| Shift Pattern | Reverse |
| Transbrake | Included |
| Torque Converter | Included |
| Converter Model | FTI SST89-0 |
| Advertised Flash Stall | 3,400–3,800 RPM |
| Torque Converter Lockup | No |
| Input Spline Count | 30 |
| Input Shaft Material | Hardened Steel |
| Bellhousing Pattern | Chevrolet |
| Transmission Case | OEM-Type Aluminum |
| Case Finish | Black |
| Transmission Pan | Deep Aluminum |
| Pan Finish | Natural |
| Clutch Hub | Billet Steel |
| Intermediate Sprag | 34-Element |
| Transmission Fluid | Included |
| Transmission Fluid Quantity | 12 Quarts |
| Transmission Cooler | Included |
| Cooler Lines | Included |
| Dipstick | Included |
| Fluid Fill Location | Case |
| Flexplate | Not Included |
| Wiring Harness | Not Included |
| Transmission Controller | Not Included |
| Condition | Professionally Remanufactured |
| Legacy Product Status | Discontinued |
Transmission / Performance Configuration
| Component | Details |
|---|---|
| Transmission Family | GM TH400 |
| Performance Level | Level 4 |
| Rated Horsepower | 900 HP |
| Forward Gears | 3 |
| Valve Body | Full Manual |
| Shift Pattern | Reverse |
| Transbrake | Integrated |
| Overdrive | Not Available |
| Torque Converter | Included |
| Recommended Application | Professionally Engineered Performance Drivetrains |
Gear Ratio Configuration
| Gear | Ratio |
|---|---|
| First Gear | 2.48:1 |
| Second Gear | 1.48:1 |
| Third Gear | 1.00:1 |
| Overdrive | Not Available |
The TH400 features a traditional three-speed automatic transmission arrangement without an overdrive gear.
Internal / Heavy-Duty Configuration
| Component | Details |
|---|---|
| Intermediate Sprag | 34-Element |
| Clutch Packs | Performance Red Race Clutches |
| Steel Plates | Performance Steel |
| Transmission Pump | High-Flow |
| Forward Clutch Hub | Billet Steel |
| Intermediate Retainer | Heavy-Duty |
| Intermediate Clutch Pack | 4-Clutch Configuration |
| Valve Body | Full Manual |
| Transmission Case | Race-Prepared OEM-Type |
| Transmission Pan | Deep Aluminum |
The Level 4 assembly incorporates upgraded components selected for its advertised performance rating.
Torque Converter Configuration
| Component | Details |
|---|---|
| Manufacturer | FTI Performance |
| Model | SST89-0 |
| Converter Type | Billet Performance Converter |
| Advertised Flash Stall | 3,400–3,800 RPM |
| Converter Cover | Billet |
| Internal Feature | Mechanical Diode |
| Anti-Ballooning Plate | Included |
| Lockup | No |
| Package Inclusion | Included |
Actual converter characteristics depend on the complete drivetrain and vehicle configuration.
Valve Body / Control Configuration
| Component | Details |
|---|---|
| Valve Body Type | Full Manual |
| Shift Pattern | Reverse |
| Transbrake | Included |
| Electronic Transmission Controller | Not Included |
| Transmission Type | 3-Speed |
| Overdrive | No |
| Lockup | No |
| Intended Application | Specialized Performance Drivetrain |
Transmission Cooling Configuration
| Component | Details |
|---|---|
| Transmission Cooler | Included |
| Cooler Lines | Included |
| Cooler Line Length | Approximately 15 Feet |
| Hose Ends | Included |
| Cooler Fittings | Included |
| Transmission Fluid | FTI Performance ATF |
| Fluid Quantity | 12 Quarts |
| Package Type | Complete Cooling Kit |
Transmission Case / Drivetrain Configuration
| Component | Details |
|---|---|
| Case Material | Aluminum |
| Case Configuration | OEM-Type |
| Case Finish | Black |
| Bellhousing Pattern | Chevrolet |
| Input Shaft | Hardened Steel |
| Input Splines | 30 |
| Clutch Hub | Billet Steel |
| Pan Type | Deep |
| Pan Material | Aluminum |
| Fluid Fill | Case |
| Yoke Compatibility | Application-Specific |
| Flexplate | Not Included |
| Drivetrain Compatibility | Requires Verification |
What’s Included
| Included Component | Details |
|---|---|
| FTI Level 4 TH400 Transmission | 1 Unit |
| FTI SST89-0 Billet Torque Converter | 1 Unit |
| Performance Full-Manual Valve Body | Installed |
| Integrated Transbrake | Included |
| Upgraded Internal Clutches | Installed |
| 34-Element Intermediate Sprag | Installed |
| Billet Forward Clutch Hub | Installed |
| Heavy-Duty Intermediate Retainer | Installed |
| Deep Aluminum Transmission Pan | Included |
| Transmission Cooler | 1 Unit |
| Cooler Lines | Approximately 15 Feet |
| Hose Ends & Fittings | Included |
| FTI Performance ATF | 12 Quarts |
| Locking Dipstick | Included |
| Dipstick Tube | Included |
| Flexplate | Not Included |
| Transmission Controller | Not Included |
| Wiring Harness | Not Included |
| Additional Installation Components | Only Where Specified |
Vehicle / Application Compatibility
The FTI TH400-4K21 is designed around the General Motors Turbo 400 transmission architecture.
| Application | Compatibility Considerations |
|---|---|
| Chevrolet Performance Vehicles | Bellhousing and Drivetrain Matching |
| GM Engine Projects | Engine and Converter Compatibility |
| Classic Chevrolet Vehicles | Transmission Mounting and Chassis Clearance |
| Custom Automotive Projects | Professional Drivetrain Engineering |
| Specialized Performance Builds | Manufacturer-Rated Component Compatibility |
| Automotive Restoration Projects | Complete Vehicle-Specific Fitment Verification |
Vehicle compatibility depends on the complete drivetrain configuration. Model year or engine family alone does not guarantee fitment.
Ideal Applications
The FTI Performance TH400-4K21 is intended for specialized automotive transmission replacement, professionally evaluated performance vehicle projects, and compatible GM drivetrain assemblies requiring the Level 4 transmission configuration.
Its package format provides the transmission, torque converter, fluid, cooler, and supporting components together, reducing the need to identify those major components separately.
Product Advantages
The FTI TH400-4K21 Level 4 Transmission Package combines an advertised 900HP capacity with a reinforced three-speed transmission assembly and matched billet torque converter.
Its comprehensive package includes performance ATF, cooling components, a locking dipstick, and a deep aluminum pan, making it more complete than a transmission-only assembly.
The Level 4 specification also includes heavy-duty clutches, a reinforced intermediate sprag, billet clutch components, and a dedicated performance valve body.
Safety & Installation Notice
This is specialized high-performance automotive equipment intended for qualified professional installation and appropriate vehicle applications.
Its full-manual valve body, transbrake configuration, and performance torque converter require careful professional assessment of the complete drivetrain and vehicle safety requirements.
Do not assume suitability for standard road vehicles or general-purpose daily driving applications.
Warranty Information
| Component | Manufacturer Warranty |
|---|---|
| Transmission | 90-Day Limited Warranty |
| Torque Converter | 1-Year Limited Warranty |
Warranty coverage is subject to FTI Performance’s written terms and applicable product eligibility. Confirm whether coverage remains available for any legacy or discontinued inventory.
Product Highlights
FTI Performance TH400-4K21 Transmission Package GM Turbo 400 / TH400 Platform Level 4 Performance Assembly 900HP Advertised Rating Three-Speed Automatic Transmission FTI SST89-0 Billet Torque Converter 3,400–3,800 RPM Advertised Stall Range Full-Manual Reverse Pattern Valve Body Integrated Transbrake 34-Element Intermediate Sprag Heavy-Duty Performance Clutches Billet Forward Clutch Hub Deep Aluminum Transmission Pan 12 Quarts FTI Performance ATF Included Complete Transmission Cooling Kit Locking Dipstick & Tube Included
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