Ferrea Racing Valves & Valve Springs

For builders asking which valve springs are best for a high-RPM K20, Evo, or WRX/STI head, Ferrea's racing line is one of the most proven answers in the sport-compact world. Its dual valve spring kits come in Drag and Endurance versions, and the 6000 Series oversize valves add flow where the stock head runs out of breath. If your build is heading past stock redline with aggressive cams, this is where you start.

Valvetrain upgrades are about control: stiffer dual springs keep the valves following the cam profile at high RPM without float, and matched retainers drop reciprocating weight so the springs can do their job. The Drag kits run maximum spring pressure for short-burst use, while Endurance kits trade a little pressure for the longevity a road-race or street build needs. Oversize 6000 Series valves increase flow but need matching seat work from a machine shop. Check your exact engine code and head specs before ordering.

Ferrea built its reputation on racing valvetrain, and this collection is the competition end of the catalog: dual valve spring kits with application-specific rates for the Honda K20, Mitsubishi 4G63 and 4B11T, and Subaru EJ platforms, plus 6000 Series performance valves. The Drag line, like the KT4019 kit for the 2004-2020 STI, targets maximum valve control for high-boost use. The Endurance line, like the KT4003 for the Honda/Acura K20 and KT4018 for the 2002-2014 WRX, balances serious pressure with the durability a street or track car needs. Supertech is the direct rival in the valvetrain aisle, with its own dual-spring kits and oversize valves for the same platforms. Browse the full performance engine valves collection, or see the main Ferrea catalog for the brand's street-oriented valvetrain parts.

Two standouts from the sampled products: the Ferrea Endurance dual valve spring kit for the Honda/Acura K20 (KT4003) is the classic high-rev K-series insurance policy, and the Ferrea Drag dual valve spring kit for the 2004-2020 Subaru STI (KT4019) is built for EJ engines pushed past stock rev limits. Our 2015+ FA engine WRX product highlight walks through more ways to strengthen a Subaru motor.

Drag vs Endurance valve springs — which do I need?

Drag kits run higher spring pressure for maximum valve control in short-burst, high-boost use. Endurance kits trade a little pressure for longer service life, suiting road racing, time attack, and street builds.

Do I need a tune after installing valve springs?

Valve springs and retainers alone don't require a tune — they don't change airflow or fueling. But if you're pairing them with aggressive cams, which is the usual reason to upgrade springs, then yes, the cam change needs a tune. Check your year and model for the right kit.

How hard is the install?

It's a head-off job for most people. The springs and retainers can be swapped with the head on using an on-car spring compressor, but oversize valves need machine-shop seat work. This is professional or experienced-DIY territory, not a driveway-first-timer project.

Are oversize valves worth it on a stock head?

Not by themselves. The 1mm-oversize valves add flow potential, but they need matching seats and port work to realize it. Pair them with a ported head and cams — that's the combination that makes the investment pay off.