Mercury Replacement Lower Unit | Verado | 90-221

SE221 Gearcase Overview

The SE221 gearcases are designed to fit three different engine families. Carefully review compatibility to ensure proper fit. Note: This unit does not include the install kit or anode kit. See related items below for add-ons.

3.0 Liter – V6 – Two Stroke (13 spline drive shaft)

• Models: SEI 221-A20, 221-A25, 221-A30
• Transitioned from SE216 to SE221 around serial # 1B504989
• Known as the “Verado Style” gearcases
• Not compatible with: Torque Master, Torque Master 2, or Sport Master
• SE221 features a 15-spline prop shaft (vs. 19-spline “Fat Shaft”)
• Referred to as the “Standard” or Fleet Master gearcase

2.6 Liter – Inline 6 Cylinder – Four Stroke (20 spline drive shaft)

• Models: SEI 221-A20F, 221-A25F, 221-A30F, 221-B20F, 221-B25F, 221-B30F
• Compatible with 200–300 HP Verado inline 6 models
• Replaces 4.8 Torpedo units only
• Not compatible with: 5.44 Torpedo, Torque Master, or Sport Master gearcases
• Note: Around 2019, Mercury released new V6/V8 engines branded “Verado” — these are not compatible with SE221

1.7 Liter – Inline 4 Cylinder – Four Stroke (20 spline drive shaft)

• Models: SEI 221-C20F, SEI 221-C25F
• Fits 135–200 HP supercharged Verado inline 4 models
• No optional gearcases beyond standard or counter-rotation
• Not compatible with: Non-Verado inline 4 models in this horsepower range (these are not supercharged, though visually similar)

Shaft Length: 20, 25, & 30"
Gear Ratio: 2.08, 1.85, and 1.75 2 & 4 Stroke