Why HKS chose I-BEAM instead of H-BEAM For TOYOTA GR86 ZN8 SUBARU BRZ ZD8 FA24 23004-AT001

 

Why HKS chose I-BEAM instead of H-BEAM For TOYOTA GR86 ZN8 SUBARU BRZ ZD8 FA24 23004-AT001

THE HKS I-BEAM CONNECTING ROD STEP1 FOR TOYOTA GR86 ZN8 SUBARU BRZ ZD8 FA24 23004-AT001 is a very serious level bottom-end upgrade for the FA24 engine found in the Toyota GR86 and Subaru BRZ. 

It is designed for high-RPM durability, forced induction builds, aggressive tuning, and endurance reliability. HKS engineered this rod together with their forged piston and crankshaft ecosystem rather than as a random standalone rod.  

1. Why HKS chose I-BEAM instead of H-BEAM

HKS intentionally selected an I-beam architecture because the FA24 is a high-revving boxer engine with long-stroke dynamics and severe tensile loading at high RPM.

Advantages of I-beam:

• Better tensile strength-to-weight ratio
• Higher resistance to rod stretch at extreme RPM
• Lower rotating mass
• Better buckling resistance during combustion events
• Narrower beam improves crankcase clearance
• Faster engine response and rev climb

Compared to many H-beam rods:

• H-beams are usually heavier
• Better for massive torque drag setups
• But can create more inertia stress at sustained RPM

Community engine builders often note that quality I-beams behave exceptionally well in high-RPM engines because they resist stretch while remaining lighter.  

For the FA24:

• HKS targeted balance
• Not just brute force
• The goal is stable high-speed endurance

This matches the GR86/BRZ philosophy:

• sharp throttle
• fast transient response
• linear rev behavior

2. Forging Material Advantage

HKS uses forged high-strength alloy material throughout the STEP1 ecosystem. Their piston system specifically uses A2618 forged alloy because of its excellent high-temperature strength.  

Benefits of forged construction:

• Grain structure aligns under forging pressure
• Much stronger than cast rods
• Better fatigue resistance
• Handles detonation better
• Survives repeated thermal cycling
• Reduced risk of microscopic cracking

Why this matters in FA24:

• Boxer engines experience complex side loading
• Turbocharging dramatically increases rod stress
• High compression + high RPM = violent tensile loads

A forged rod survives:

• hard launches
• sustained track heat
• repeated redline pulls
• turbo boost spikes

far better than stock powdered-metal rods.

3. Molybdenum Coating Advantage

HKS includes molybdenum technology within the piston/rotating assembly philosophy. Their FA24 STEP1 piston kit uses a two-layer molybdenum coating to reduce friction.  

Why this matters:

Moly coating benefits

Reduced friction

• Less parasitic drag
• Faster revving
• Smoother piston movement

Improved oil retention

• Moly surfaces hold lubrication better
• Critical during cold starts
• Helps under high G-force cornering

Heat resistance

• Moly survives extremely high temperatures
• Prevents scuffing under boost

Lower wear

• Reduced piston skirt abrasion
• Less cylinder wall damage

Better emergency protection

If oil film momentarily weakens:

• moly acts as sacrificial anti-friction layer
• helps prevent catastrophic scoring

This is especially important in:

• track GR86 builds
• turbo FA24s
• endurance driving
• repeated canyon runs

4. Cracked Rod Technology

HKS uses cracked-cap rod technology.  

Why this is advanced:

• Rod cap fractures naturally along engineered grain lines
• Creates perfectly matching surfaces
• Better alignment precision
• More stable bearing housing geometry
• Less cap walk at high RPM

This improves:

• bearing stability
• oil film consistency
• crankshaft accuracy

At 8000+ RPM:
tiny distortions matter enormously.

5. Why this rod is excellent for turbo FA24

The FA24 creates strong midrange torque.

Turbocharging increases:

• cylinder pressure
• rod compression load
• tensile load during exhaust/intake overlap

The HKS rod helps by:

• resisting deformation
• maintaining bearing alignment
• reducing rotating inertia
• surviving detonation events better

HKS themselves recommend stronger rod/crank combinations for turbo applications generating high torque.  

6. Real Engineering Philosophy of HKS STEP1

STEP1 is not “full drag insanity.”

It is:

• OEM+ engineering
• motorsport reliability
• high-RPM endurance
• street-track balance
• refined response

This is classic Japanese tuning philosophy:

• precision
• balance
• thermal stability
• drivability

rather than only chasing dyno numbers.

Why HKS chose I-BEAM instead of H-BEAM For TOYOTA GR86 ZN8 SUBARU BRZ ZD8 FA24 23004-AT001