Reinforced valve spring kit Ford Mustang 2.3 EcoBoost C23HD0D N38H N48H
Kit of 16 reinforced valve springs for the 2.3 EcoBoost engine of the Ford Mustang.
- Brand: FERREA
- Engines: 2.3 EcoBoost C23HD0D, N38H, N48H, Ford Mustang
- Springs: single
Ford engine covered
This kit suits the 2.3 EcoBoost, a turbocharged in-line four-cylinder of 2.3 litres with 16 valves and two overhead camshafts. It powers the Ford Mustang from 2014 (C23HD0D, N38H, N48H) and, since 2025, the second-generation Ford Everest.
On all 16 valves the kit replaces the spring, the upper retainer, the lower spring seat and the collets. FERREA supplies a single spring, titanium upper retainers, lower spring seats and its own collets.
FERREA reinforced valve spring kit
When the cam lobe drops away, the spring has to press the valve onto its seat again. Past a certain rpm, a spring lacking stiffness lets the valve lift off the cam, return late and strike the piston: valve float.
Set at 37.8 mm, this single spring exerts 334 N on the seat and 712 N after 10 mm of lift, with titanium upper retainers.
Valve spring kit technical specification
| Part number | Brand | Springs | Outer / inner Ø | Seat pressure | Open pressure | Rate | Max lift | Kit contents |
|---|---|---|---|---|---|---|---|---|
| KT4008 | FERREA | Single | Outer 24.6 mm Inner 17.4 mm |
334 N at 37.8 mm | 712 N at 10 mm | 37.8 N/mm | 12.7 mm | 16 springs, 16 titanium upper retainers, 16 lower spring seats, 16 sets of collets |
Valve spring kit fitting details
| Part | Ford original | Reinforced spring kit |
|---|---|---|
| Spring | Kit specific: S10163 (single) | |
| Retainer | Kit specific: E11135 (titanium) | |
| Spring seat | Kit specific: SL1147 | |
| Collets | Kit specific: K10113 |
FERREA kit KT4008 contains 16 S10163 springs, 16 E11135 titanium upper retainers, 16 SL1147 lower spring seats and 16 sets of K10113 collets.
Read with the valve fully closed, installed height is the distance separating the two retainers, lower and upper. FERREA states the seat load for one height only; installed higher, once the seats have been recut, for instance, the spring loses its rate in newtons per extra millimetre (refer to the specification table, then height and load below).
| FERREA | |
|---|---|
| Installed height | 37.8 mm |
| Seat pressure at this height | 334 N |
Technical guide
Our brands
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FERREA Racing Components comes from Florida: based in Fort Lauderdale since 1978 and founded by two Argentine engine builders, it designs and machines its own valves, springs, retainers and tappets, found on NASCAR, dragster and circuit cars. |
How to choose
The firmer the spring, the higher the engine can rev and the more boost or camshaft aggression it tolerates before valves float. This kit gives 334 N on the seat and 712 N after 10 mm of lift. Before ordering, confirm that your camshaft does not lift beyond 12.7 mm, the ceiling of this kit; a dial gauge settles it in minutes. It takes little time and avoids a nasty surprise.
| Criterion | Key point |
|---|---|
| Choosing the pressure | Three parameters set the load: cam lift, the engine speed you are aiming for and boost. When they rise, the spring has to be firmer, while respecting the maximum lift of the kit. Going beyond what is needed gains nothing: an excessive spring damages the cams and punishes the valves. Check the real lift rather than an approximate figure. |
| Single or double spring | The KT4008 has one spring per valve and no inner spring, so that spring takes the entire load. A double spring fits two coils one inside the other to spread the effort and calm their vibrations; that is not the design of this kit, which is right as long as this load covers your engine speed. |
When reinforced springs become necessary
- Camshaft whose lift exceeds the standard one
- Rev limit lifted by a new map
- Boost raised on the 2.3 EcoBoost
- Frequent use on circuit, in drift or in rally
- Worn springs, valve float at high rpm
Compatible vehicles
| Model | Engine code | Power | Years |
|---|---|---|---|
| Ford Mustang (FM, FN) 2.3 EcoBoost | C23HD0D, N38H, N48H | 2014-2023 | |
| Ford Mustang 2.3 EcoBoost (P8T, P8U) | From 2014 | ||
| Ford Everest II (UB) 2.3 GTDi EcoBoost 4x4 | From 2025 |
Related products
Head already off to renew the springs? Fit new valves too, inlet and exhaust, in the same session. The ones made for this engine are below:
| FORD 2.3 EcoBoost inlet valves → |
| FORD Mustang 2.3 EcoBoost exhaust valves → |
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Brand
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ReferenceKT4008
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