MMR Valve Spring & Retainer Upgrade Kit (400889) - 2018+ Mustang & F-150 5.0
When maximum RPM stability and race-proven durability matter, the MMR Valve Spring & Retainer Upgrade Kit delivers. Engineered for high-lift camshafts and extreme engine speeds, this kit is trusted in the fastest Coyote builds on the planet—including record-setting 6-second combinations. It’s the go-to upgrade for serious street, strip, and road race applications pushing well beyond factory limits.
This complete drop-in kit includes precision beehive-style valve springs and lightweight retainers designed to control valve motion with camshaft lifts up to .600" and engine speeds approaching 10,000 RPM. Shot-peened and super-finished for long-term durability, these springs are compatible with all factory-style valves and locks. Ideal for Boss and GT-based engines, cam limiters or phaser lockouts are recommended for aggressive setups.
Features
- High-performance valve spring and retainer upgrade for Coyote 5.0 engines
- Supports camshaft lifts up to .600"
- Designed for extreme RPM capability (up to 10,000 RPM potential)
- Beehive-style, super-finished, shot-peened valve springs
- Lightweight, high-strength retainers included
- Direct replacement for factory Boss and GT valve springs
- Compatible with all valves and valve locks
- Proven in championship-winning and world-record Coyote builds
Fitment
- 2018 Ford Mustang GT 5.0
- 2019 Ford Mustang GT 5.0
- 2020 Ford Mustang GT 5.0
- 2021 Ford Mustang GT 5.0
- 2022 Ford Mustang GT 5.0
- 2023 Ford Mustang GT 5.0
- 2024 Ford Mustang GT 5.0
- 2025 Ford Mustang GT 5.0
- 2026 Ford Mustang GT 5.0
- 2018 Ford F-150 5.0
- 2019 Ford F-150 5.0
- 2020 Ford F-150 5.0
- 2021 Ford F-150 5.0
- 2022 Ford F-150 5.0
- 2023 Ford F-150 5.0
- 2024 Ford F-150 5.0
- 2025 Ford F-150 5.0
- 2026 Ford F-150 5.0
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