MerCruiser Alpha One Gen I complete standard-rotation sterndrive

MERCRUISER BRAVO UPPER REPLACEMENTS

Bravo Upper Applications

Shop SE121 replacement upper units for MerCruiser Bravo One, Bravo Two and Bravo Three applications. Compare 29/27, 30/23 and 32/27 tooth-count configurations and verify your drive ratio before ordering.

Bravo Upper Applications

Shop MerCruiser Bravo upper unit applications — gear cases that transfer power from the input shaft to the lower unit in Bravo sterndrives. Available in multiple tooth-count ratios to match your specific Bravo application.

Find the correct Bravo upper application part for your sterndrive rebuild below.

Sidebar
Filter
  • 10
  • 15
  • 20
  • 25
  • 30
  • 50
  • Featured
  • Most relevant
  • Best selling
  • Alphabetically, A-Z
  • Alphabetically, Z-A
  • Price, low to high
  • Price, high to low
  • Date, old to new
  • Date, new to old
Sort

Sort by:

  • Featured
  • Most relevant
  • Best selling
  • Alphabetically, A-Z
  • Alphabetically, Z-A
  • Price, low to high
  • Price, high to low
  • Date, old to new
  • Date, new to old
  • Stern Drive Upper Unit 90-121-01C with 29/27 Tooth Gear Ratio and Oil Recirculation Case - Mariners Warehouse

    Sterndrive Upper Unit | SE121 | 30/23 Tooth Count SKU: SE90-121-01A
    MPN: SE121-Upper3023

    $2,795.00
    $3,102.45
    $2,795.00
    Restore dependable stern drive propulsion with this high-performance upper unit engineered to handle up to 425HP. Featuring the advanced newer style case equipped with a front-facing oil recirculation system, this unit delivers enhanced thermal efficiency and smooth power transfer. Constructed for demanding marine environments,...
    $2,795.00
    $3,102.45
    $2,795.00
  • Stern Drive Upper Unit 90-121-01C with 29/27 Tooth Gear Ratio and Oil Recirculation Case - Mariners Warehouse

    Sterndrive Upper Unit | SE121 | 32/27 Tooth Count SKU: SE90-121-01B
    MPN: SE121-Upper3227

    $2,795.00
    $3,102.45
    $2,795.00
    Restore maximum drivetrain performance with this premium Upper Drive engineered for high-demand sterndrive systems. Built to withstand demanding marine conditions, this unit delivers consistent power transfer for vessels rated up to 425HP. Featuring a newer style case with an integrated front-facing oil recirculation system,...
    $2,795.00
    $3,102.45
    $2,795.00
  • Stern Drive Upper Unit 90-121-01C with 29/27 Tooth Gear Ratio and Oil Recirculation Case - Mariners Warehouse

    Stern Drive Upper Unit | 90-121-01C | 29/27 Tooth Gear Ratio SKU: SE90-121-01C
    MPN: SE121-Upper2927

    $2,795.00
    $3,102.45
    $2,795.00
    Restore dependable stern drive power with this premium aftermarket upper drive housing engineered for high-performance sterndrive systems. This upper unit features a modern case design equipped with an integrated front-facing oil recirculation system to optimize thermal management and lubrication. Manufactured for durability in demanding...
    $2,795.00
    $3,102.45
    $2,795.00

A Clearer Way to Select Your Replacement Drive

Compare the configuration details that matter before choosing a sterndrive.

OEM-COMPATIBLE FITMENT

Engineered for direct replacement

25+ YEARS SERVING BOATERS

Trusted marine parts experience

3-YEAR WARRANTY

Coverage on select lower units

FITMENT SUPPORT

We'll help verify your lower unit

How to Choose the Correct Bravo Upper Unit

Choosing a MerCruiser Bravo upper unit requires more than identifying whether you have a Bravo One, Bravo Two or Bravo Three drive. Different SE121 upper tooth-count configurations are paired with specific lower assemblies to produce different overall drive ratios.

Start by identifying the existing Bravo drive family and current overall ratio. Then check the existing upper or lower part number, drive serial number and the tooth-count configuration when available. The retained lower must also be compatible with the replacement upper.

Before ordering a Bravo upper unit, verify:

  • Bravo One, Bravo Two or Bravo Three drive family
  • Existing overall gear ratio
  • Drive or engine serial number
  • Existing upper-unit identification
  • Existing lower-unit identification
  • 29/27, 30/23 or 32/27 tooth count
  • Compatible oil-passage configuration
  • Any application exclusions shown on the product page

SE121 Bravo Upper Unit Comparison


Use this table to compare two SE121 Bravo upper-unit configurations currently represented in the collection. It is a shopping guide, not a universal compatibility chart. Final fitment must be confirmed from the existing drive ratio, retained lower assembly and installed drive information.

SE121 29/27 Upper Unit SE121 30/23 Upper Unit
Tooth count: 29/27 Tooth count: 30/23
Manufacturer model: SE121 Manufacturer model: SE121
SKU / MPN: SE90-121-01C SKU / MPN: SE90-121-01A
Bravo One application: 1.36 overall ratio Bravo One application: 1.65 overall ratio
Bravo Two applications: 1.50 and 1.81 overall ratios Bravo Two application: 2.20 overall ratio
Bravo Three applications: 1.36 and 1.81 overall ratios Bravo Three applications: 2.20 and 2.43 overall ratios
Not intended as a replacement for Bravo X, XR or XZ applications Not intended as a replacement for Bravo X, XR or XZ applications
Confirm the retained lower has the compatible oil-passage configuration Confirm the retained lower has the compatible oil-passage configuration
Verify drive family, overall ratio, serial information and retained lower before ordering Verify drive family, overall ratio, serial information and retained lower before ordering

Do not choose an SE121 Bravo upper unit from tooth count or drive-family name alone. Confirm the existing overall drive ratio, serial information and retained lower compatibility before ordering.

Upper Unit, Lower Unit or Complete Bravo Sterndrive?

A Bravo upper unit, lower unit and complete sterndrive solve different repair needs. Confirm which assembly has failed and whether the retained components are compatible before purchasing a replacement.

Complete Bravo Sterndrive

  • Combines the major upper and lower sterndrive assemblies into a complete replacement drive.
  • May be appropriate when both assemblies are damaged, worn or incompatible.
  • Can simplify replacement when retaining the existing upper or lower is not the correct repair path.
  • Confirm Bravo One, Bravo Two or Bravo Three application and required overall gear ratio.
  • Verify serial information and product-specific application details before ordering.

Upper Unit

  • Contains the upper driveshaft housing, gears and related internal components.
  • Suitable when inspection confirms the failure is isolated to the upper assembly.
  • The retained Bravo lower unit must remain serviceable and compatible with the replacement upper.
  • Confirm the overall drive ratio and required SE121 tooth-count configuration before ordering.
  • Verify the lower-unit oil-passage configuration and installed drive identifiers.

Lower Unit

  • The lower gearcase assembly located beneath the Bravo upper housing.
  • Suitable when damage or failure is isolated to the lower assembly.
  • The retained upper unit must remain serviceable and compatible with the replacement lower.
  • Confirm the applicable Bravo drive family and lower-unit configuration before ordering.
  • Verify water-pickup style, installed identifiers and overall drive requirements.
An informational comparison graphic titled 'STANDARD VS COUNTER ROTATION' showing two outboard motors and two propellers, with text explaining the difference in propeller direction when viewed from behind. The background is a real marina scene with water and boats, but the image functions as an explanatory diagram rather than a straightforward product photo.

Standard vs Counter Rotation

Standard and counter rotation describe the direction the propeller turns when the boat is moving forward. Standard rotation generally uses a right-hand propeller, while counter rotation turns in the opposite direction.

Counter-rotation setups are often used in certain twin-engine or matched-drive configurations to help balance propeller forces. Always confirm rotation from the existing drive identification and propeller setup before ordering replacement sterndrive components; do not rely only on port or starboard position.

Explore More MerCruiser Bravo Drive Options

A Bravo upper unit is only one part of the MerCruiser Bravo sterndrive system. If your repair requires a lower assembly, complete drive or a different Bravo configuration, continue through the related Bravo collections rather than ordering an upper that does not match the repair.

Use the existing drive family, overall gear ratio, serial information and retained components to choose the correct shopping path

  1. Bravo Sterndrive Applications

    Explore the broader MerCruiser Bravo collection for complete drives, upper units, lower units and related Bravo replacement applications.

    Explore Bravo Applications

  2. Bravo Lower Units

    Browse replacement Bravo lower-unit applications when the failed component is below the upper housing and your retained upper remains compatible.

    Shop Bravo Lower Units

  3. MerCruiser Sterndrives

    Compare Alpha One and Bravo drive-family replacement options from the main MerCruiser sterndrive collection.

    Shop MerCruiser Sterndrives

Know What You're Ordering

This collection is for SE121 replacement Bravo upper assemblies. The upper unit is a separate component from the Bravo lower unit and complete sterndrive assembly.

Supplier application information states that the installation kit and anode kit are not included with these SE121 upper units. Review the individual product listing before purchase to confirm the exact contents and any additional components required for your installation.

What Customers Say

Helpful information for selecting the SE121 upper unit

The Bravo upper unit information made it easier to understand which SE121 configuration matched my existing sterndrive setup. The tooth-count details were especially useful when comparing the available options. I would recommend confirming the original upper unit specifications before ordering.
Brandon Foster Verified buyer
August 2026

Clear guidance for the 30/23 tooth configuration

I was looking at the SE121 upper unit with the 30/23 tooth count, and the product information helped make the differences between the available Bravo upper units much clearer. The fitment details were useful and made it easier to verify the existing drive before installation.
Kevin Marshall Verified buyer
June 2026

Easy to compare the Bravo upper unit options

The collection made it straightforward to compare the SE121 30/23, 32/27, and 29/27 upper unit configurations. Having the tooth counts clearly identified was helpful because these units may look similar at first. Checking the existing gearing before ordering is definitely important.
Jason Whitaker Verified buyer
March 2026

Good fitment details for the 32/27 SE121

The information for the SE121 32/27 tooth upper unit was clear and easy to follow. I appreciated that the product configuration was identified directly instead of relying only on general Bravo compatibility. The packaging and installation preparation information also made the process easier to understand.
Trevor Collins Verified buyer
October 2025

Useful details for identifying the 29/27 upper unit

The 29/27 tooth configuration was the main detail I needed to confirm when reviewing the Bravo upper unit options. The page made the SE121 choices easier to distinguish and helped avoid selecting an upper unit based only on appearance. Verifying the existing drive specifications first is the best approach.
Derek Hamilton Verified buyer
May 2025

Helpful Guides

Use these guides to identify your MerCruiser drive, understand gear-ratio selection and decide whether you need a complete sterndrive, upper unit or lower unit.

Marine technician holding a MerCruiser Bravo upper unit gearcase near a serial number tag on a boat transom in a repair workshop

How to Identify Your MerCruiser Bravo Drive Before Buying an Upper Unit

How to Identify Your MerCruiser Bravo Drive Before Buying an Upper Unit Ordering a Bravo upper unit without first confirming...

Read More →
Close-up macro photo of a MerCruiser Bravo upper unit gear set showing precise gear teeth on a workbench

SE121 Bravo Upper Guide: 29/27 vs 30/23 vs 32/27

SE121 Bravo Upper Guide: 29/27 vs 30/23 vs 32/27 The SE121 Bravo upper unit family is organized around tooth-count pairings...

Read More →
Bravo Upper Unit vs Lower Unit vs Complete Sterndrive

Bravo Upper Unit vs Lower Unit vs Complete Sterndrive

Bravo Upper Unit vs Lower Unit vs Complete Sterndrive Deciding between a Bravo upper unit, a lower unit, or a...

Read More →

Frequently Asked Questions

How do I know which MerCruiser Bravo upper unit I need?

Start by identifying your Bravo drive family and existing overall gear ratio. Then verify the upper tooth-count configuration, drive serial number, retained lower assembly and existing part numbers before choosing a 29/27, 30/23 or 32/27 SE121 upper.

What is the difference between the 29/27, 30/23 and 32/27 SE121 upper units?

They use different upper gear-tooth configurations and correspond with different overall Bravo drive ratios. The correct configuration depends on the Bravo family, required overall ratio and compatible retained lower assembly.

Which SE121 upper fits a Bravo One sterndrive?

The available SE121 configurations cover different Bravo One ratios. The 29/27 is listed for 1.36, the 30/23 for 1.65 and the 32/27 for 1.50 applications. Confirm the existing drive identifiers and retained lower before ordering.

Which SE121 upper fits a Bravo Two sterndrive?

SE121 upper selection for Bravo Two depends on the overall ratio. Available applications include 1.50 and 1.81 with the 29/27 configuration, 2.20 with the 30/23 and 1.65 or 2.00 with the 32/27 configuration.

Which SE121 upper fits a Bravo Three sterndrive?

Bravo Three applications vary by overall ratio. The 29/27 configuration covers listed 1.36 and 1.81 applications, the 30/23 covers 2.20 and 2.43, and the 32/27 covers 1.50, 1.65 and 2.00 applications.

Can I choose a Bravo upper unit from the gear ratio alone?

No. Gear ratio is an important selection factor, but the drive family, serial information, retained lower, upper tooth count and product-specific compatibility should also be confirmed before ordering.

Will an SE121 upper fit every Bravo lower unit?

No. The retained lower must be compatible with the selected upper, including the required oil-passage configuration. Supplier information specifies the newer front oil-recirculation passage and identifies drive serial 0F730000 and above for this configuration.

Do these SE121 upper units replace Bravo X, XR or XZ drives?

No. The SE121 upper units in this collection are not listed as replacements for Bravo X, XR or XZ drive applications. Use the correct product family for those drives.

Is a Bravo upper unit the same as a complete Bravo sterndrive?

No. A Bravo upper unit is only the upper assembly. A complete Bravo sterndrive includes a broader drive assembly, while the lower unit is also available as a separate replacement component.

What information should I send for Bravo upper-unit fitment help?

Send your Bravo drive family, engine and drive serial numbers, current overall ratio, existing upper and lower part numbers when visible, and clear photos of the sterndrive and identification labels. This information helps narrow the correct SE121 upper configuration.

Need Help?

Still Can't Find the Right Marine Part?

Finding the right replacement part shouldn't be frustrating. If you can't locate the marine part you need, our experienced support team is here to help. Whether you have a part number, engine model, or simply need expert guidance, we'll help you find the correct replacement so you can get back on the water with confidence.

Contact Marine Experts Browse All Mercruiser

Trusted by 50,000+ boat owners across the USA

A man wearing a navy blue polo shirt with a circular logo sits at a desk holding a metal engine component, with a laptop in front of him and a boat propeller on the table. A dark blue informational overlay on the right lists benefits like 'Talk to an Expert' and 'Find the Right Part'.

  • Expert Marine Support

    Our team has years of experience in marine parts.

  • Fast Response

    We respond quickly to get you the help you need.

  • Find Compatible Parts

    We make sure you get the right part the first time.

  • Huge Selection

    Access to 50,000+ marine parts & accessories.

Have a Part Number or Engine Model?

Send it to us and our experts will help you find the exact part you need.

Recently Viewed Products