Precision Above the Block
In Chapter 1, Grimace’s factory 3.0-litre S58 began its transformation into a fully forged 3.4-litre stroker engine, laying the foundation for our ambitious 1,500-horsepower goal.
With the forged 3.4-litre stroker short block now complete, attention shifts to the cylinder head.
While the forged rotating assembly provides the strength to withstand enormous cylinder pressures, the cylinder head is responsible for something equally important—how efficiently the engine breathes. Airflow, valve control and precision assembly all play a critical role in producing reliable horsepower, especially in a high-boost single turbo application.
This chapter follows the complete assembly of Grimace’s upgraded cylinder head before it is finally united with the freshly built 3.4-litre stroker engine, bringing the project one major step closer to completion.
Preparing the Cylinder Head
Following weeks of careful machining and preparation, Grimace’s S58 cylinder head returned from the machine shop after receiving a full CNC port and polish.
Every intake and exhaust runner was carefully reshaped to optimise airflow into and out of the combustion chamber while maintaining the reliability expected from a road-going performance engine. Improving airflow is critical in any high-horsepower build, particularly when paired with the substantially larger turbocharger planned later in the series.
With the machining complete, assembly could finally begin.
Building an S58 Ready for 1,500 Horsepower
Every component installed into Grimace’s cylinder head has been carefully selected to support significantly higher engine speeds, boost pressures and airflow than the factory engine was ever designed to handle.
Rather than relying on individual upgrades, the entire valvetrain has been engineered as a complete package to complement the forged stroker bottom end and the next stage of the build.
At this level of performance, every component must work together. There’s little value in upgrading one part while leaving another as the weak link, which is why Grimace’s cylinder head has been developed as a complete system rather than a collection of individual parts.
The upgraded cylinder head features:
- RK Autowerks CNC Port & Polished Cylinder Head
- GSC Billet Camshafts
- GSC Upgraded Valves
- GSC Upgraded Valve Springs
- Titanium Retainer Kit
- GSC Power Division Components
- RK Autowerks S58 Fire Rings
- OEM BMW Multi-Layer Steel (MLS) Head Gasket
- ARP Custom Head Studs
Each component plays an important role in improving airflow, maintaining valve stability at high RPM and ensuring the engine remains reliable under the extreme cylinder pressures expected from Grimace’s future single turbo setup.
Marrying the Head
With the cylinder head fully assembled, it was finally time to unite the top and bottom halves of the engine.
Using an OEM BMW Multi-Layer Steel (MLS) Head Gasket, RK Autowerks Fire Rings and ARP Custom Head Studs, the completed cylinder head was carefully lowered onto the freshly assembled 3.4-litre stroker bottom end.
While the OEM head gasket provides the primary seal between the engine block and cylinder head, the addition of RK Autowerks Fire Rings reinforces the sealing around each combustion chamber, helping contain the extreme cylinder pressures expected from Grimace’s future single turbo setup. Combined with the superior clamping force of the ARP Custom Head Studs, the assembly is designed to provide the reliability required for a 1,500-horsepower S58.
For any engine builder, this is one of the defining moments of the entire build.
After weeks of machining, measuring, cleaning and assembling hundreds of individual components, Grimace officially became a complete long motor.
Although there’s still a significant amount of work ahead, the project is beginning to resemble the finished engine that will eventually power one of Australia’s most ambitious S58 builds.
Attention to Detail
One of the defining goals of the Grimace project has always been to showcase what’s possible when every stage of a build is completed under one roof.
From engine machining and assembly through to fabrication, drivetrain strengthening and final ECU calibration on our Mainline ProHub 3600CS AWD Hub Dyno, every step remains in-house.
That means every measurement, clearance and assembly procedure can be verified by the same team that will ultimately calibrate the finished engine on the dyno.
That level of control allows every component to be inspected, measured and assembled exactly as intended before Grimace eventually fires into life for the first time.
Build Progress
✅ Chapter 1 — Bottom End: From 3.0L to 3.4L
✅ Chapter 2 — Head Assembly (Current)
⬜ Chapter 3 — Gearbox & Transfer Case Build
⬜ Chapter 4 — The Single Turbo Transformation
⬜ Chapter 5 — Everything Behind the Power
⬜ Chapter 6 — Engine & Gearbox Reunited
⬜ Chapter 7 — First Start, Calibration & Dyno Development
⬜ Chapter 8 — Final Results
What’s Next?
With the long motor now complete, attention shifts to the next critical piece of the puzzle—the drivetrain.
There’s little point building a 1,500-horsepower engine without ensuring the transmission and transfer case are capable of reliably putting that power to the ground.
In Chapter 3, we’ll strip down Grimace’s gearbox and transfer case, upgrading critical internal components to prepare the driveline for the power that lies ahead.
Only once the drivetrain is ready will the project return to one of the most anticipated stages of the build—the complete single turbo transformation.
Stay tuned as Grimace’s drivetrain begins its own evolution.
Watch Chapter 2
Frequently Asked Questions
Why port and polish the cylinder head?
Porting and polishing improves airflow through the intake and exhaust ports, allowing the engine to move a greater volume of air more efficiently. Combined with larger turbochargers and upgraded camshafts, improved airflow directly contributes to increased horsepower and overall engine efficiency.
Why upgrade the valve springs and retainers?
As boost pressure and engine speed increase, maintaining accurate valve control becomes critical. Upgraded valve springs and lightweight titanium retainers help prevent valve float while improving durability during sustained high-RPM operation.
Why install billet camshafts?
Billet camshafts optimise valve lift and duration, allowing the engine to make better use of the increased airflow provided by the ported cylinder head and larger turbocharger. They play a significant role in maximising power throughout the rev range.
What do fire rings do?
On high-boost turbocharged engines, combustion pressures increase significantly. Fire rings reinforce the seal around each cylinder, helping prevent combustion gases from escaping between the cylinder head and engine block. When combined with an OEM head gasket and ARP head studs, they provide the sealing integrity required for extreme horsepower applications.
Why is the cylinder head so important in a high-horsepower engine?
While the forged bottom end provides the strength to survive extreme power levels, the cylinder head determines how efficiently the engine can breathe. Airflow, combustion efficiency and valvetrain stability all begin here, making it one of the most important components in any serious engine build.
Components Featured in This Chapter
- RK Autowerks CNC Port & Polished S58 Cylinder Head
- GSC Billet Camshafts
- GSC Upgraded Valves
- GSC Upgraded Valve Springs
- Titanium Retainer Kit
- GSC Power Division Components
- RK Autowerks S58 Fire Rings
- OEM BMW Multi-Layer Steel (MLS) Head Gasket
- ARP Custom Head Studs
Missed Chapter 1?
If you’re just joining the journey, start with Grimace Build Series – Chapter 1: From 3.0L to 3.4L, where we transform the factory S58 into a fully forged 3.4-litre stroker bottom end—the foundation of our 1,500-horsepower vision.
Grimace isn’t just an engine build—it’s a complete in-house engineering project documenting every step towards one of Australia’s most ambitious S58-powered BMWs. We’ll see you in Chapter 3. 💜
