4R250 Sport Engine MINI R53 | R52 | Cooper S | JCW

WEEKEND RACER REPLACEMENT
The 4R250 Sport engine is the ideal choice for MINI Gen 1 drivers looking for increased performance without compromising daily reliability. Whether you're a weekend racer or simply want a stronger, more capable engine, the 4R250 delivers enhanced power and durability compared to the stock unit.
Designed as a direct-fit replacement for the MINI Gen 1 engine, each 4R250 engine comes fully assembled, from oil sump to rocker cover, and is prepared for smooth integration into your project. When paired with our Engine Installation Package, it provides a true plug-and-play solution to get your MINI back on the road, fast!

BUILT FOR PERFORMANCE
The 4R250 engine is built for MINI enthusiasts seeking a performance-ready upgrade capable of supporting up to 250 BHP. At its core is a carefully inspected bare cast block, precisely machined to accept 77.25 mm forged Wössner pistons, designed to handle increased boost and power levels. The rotating assembly combines an OEM crankshaft with OEM connecting rods fitted with ARP 2000 bolts for improved clamping strength and reliability under load. KING race-spec bearings are used throughout to provide increased durability where standard OEM bearings fall short. To complete the bottom end, a brand-new OEM-quality oil pump is installed, ensuring consistent oil flow under demanding conditions.

The block is then paired with our 4R250 cylinder head, built from a thoroughly inspected OEM casting and assembled with a combination of SUPERTECH and OEM-quality valvetrain components. ARP 2000 head studs are installed to deliver superior clamping force, keeping the cylinder head firmly secured to the block and ensuring a reliable seal under boost. During final assembly, the engine is fitted with a completely new timing system, including a brand-new chain, guides, tensioner, and timing gears, and is completed using all-new gaskets, seals, and essential fasteners to ensure long-term reliability.

4R250 SHORT BLOCK SECTION

COMPLETELY CHECKED
All engine blocks are thoroughly cleaned, inside and out, to eliminate any debris or residue from previous use. Each casting is then pressure tested and carefully inspected to ensure it is free from cracks, damaged threads, or other defects that could cause future issues. This meticulous process ensures that every block is in optimal condition and ready to perform

MACHINED TO LAST
All engine blocks are precision-machined to the highest tolerances. Each block is bored and honed to accept oversized Wössner forged pistons, with bores finished to the correct surface roughness, straightness, and roundness, ensuring optimal piston ring sealing. The OEM crankshaft and connecting rods are carefully inspected and machined if necessary to ensure they meet the required tolerances. The block deck is then resurfaced to achieve maximum flatness and the ideal finish for a reliable seal with the MLS head gasket. Finally, each engine is painted to protect against corrosion and external elements.

BUILD TO PERFORM
The 4R250 short block is designed as a mild performance upgrade for modified MINIs operating under increased boost. It retains the proven forged 77.25 mm Wössner pistons from our standard 4RSTD package but adds key reinforcements to improve durability under higher loads. The OEM connecting rods are fitted with ARP 2000 bolts to increase clamping strength, while KING race-spec bearings provide greater resilience against elevated cylinder pressures. Together, these enhancements make the 4R250 short block better suited for performance builds requiring added strength and reliability.

4R250 CYLINDER HEADS SECTION

UPGRADED PERFORMANCE REPLACEMENT
The 4R250 cylinder head is designed as a direct-fit performance upgrade for the MINI Gen 1 engine, ideal for modified builds that demand increased strength and reliability. Whether your engine has suffered a catastrophic failure or you don't have a usable OEM core to begin with, the 4R250 head is a significant step up from stock. Each head comes fully assembled with a combination of OEM-quality and high-performance SUPERTECH valvetrain components, and is prepared for smooth integration into your engine build. When paired with our 4R250 short block, it offers a true plug-and-play solution with enhanced durability and flow performance.

COMPLETELY CHECKED
Before machining, all cylinder head castings are fully disassembled and cleaned to remove any residual oil, carbon buildup, or debris from previous use. Each casting then undergoes pressure testing and visual inspection to verify it is free from cracks, warped surfaces, damaged threads, or other potential defects. Only heads that meet our quality standards proceed to the machining stage.

MACHINED TO PERFORM
The machining process begins with replacing all valve guides with our manganese bronze designed guides, tailored for optimal fit, heat transfer, and durability. Each guide is precision-honed to ensure the correct valve-to-guide clearance, promoting proper lubrication and long-term reliability.
The exhaust side is significantly upgraded using +2.3 mm oversized SUPERTECH valves. To support the larger valves, the seats are machined with an optimized multi-angle profile for maximum flow. The exhaust ports are fully ported to complement the larger valve size, delivering a substantial performance gain over the stock configuration.
On the intake side, the OEM valves are retained, but the ports are pocket-ported to improve flow while maintaining airspeed and velocity, enhancing drivability and low-end response.
After all porting and seat work is complete, the deck surface is resurfaced to achieve maximum flatness and the correct finish for a reliable seal with the MLS head gasket. Finally, the cylinder head undergoes a complete cleaning to remove any debris or residue from the machining process, preparing it for final assembly.

BUILT TO DELIVER
All 4R250 cylinder heads are assembled with a combination of OEM- and performance-grade components. Standard-size 30.3 mm intake valves are paired with +2.3 mm oversized SUPERTECH exhaust valves to increase flow capacity. OEM valve springs, retainers, and keepers are used for reliable valvetrain control, while Viton valve stem seals ensure long-term oil control.

WHAT MAKES PORTING BETTER?
Cylinder head porting is a proven method to improve the airflow efficiency of the cylinder head. At 4RevisionEngines, we carefully reshape the ports to maximize flow while maintaining critical air velocity, focusing on flow quality, not just port size. All porting work is developed and verified in-house using our flow bench to ensure consistent, measurable gains in cylinder head performance.

OPTIONAL CAMSHAFTS
If you're targeting more power from your 4R300 head package, upgrading the camshaft is essential. We offer several camshaft options to suit different setups. For improved low-end torque and drivability, we recommend the CatCams 1302461. For increased high-RPM performance and maximum top-end power, the CatCams 1302469 is the ideal choice. Both profiles provide noticeable gains in power and torque across the entire RPM range.

ENGINE INSTALLATION PACKAGE
Make your engine swap easier and more cost-effective by adding our Engine Installation Package to your order. To ensure the best performance and reliability from your 4Revision Engines build, it’s essential to use high-quality components that protect your investment. Each kit includes the correct fluids, a belt, all necessary gaskets, a set of spark plugs, pulleys, and a belt tensioner, everything you need for a smooth installation. Compatible with all MINI Gen 1 engines, this package offers the right parts at a discounted rate, saving you both time and hassle.

POWER RATING
The 4R250 engine is engineered to support power outputs of up to 250 BHP when paired with the appropriate supporting modifications, such as smaller supercharger pulleys, larger injectors, improved intercooling, colder intake air, and better-flowing exhaust manifolds.

WHAT’S IN IT

Short Block:
Block – OEM machined casting
Pistons – 77.25 mm oversized Wössner forged pistons
Crankshaft – OEM crankshaft
Connecting Rods – OEM rods fitted with ARP 2000 bolts
Oil Pump – Brand-new OEM-quality oil pump
Rod / Main Bearings – KING race-spec bearings
Timing – Complete new kit including gears, guides, chain, and tensioner
Painted – Color on request

Cylinder Head:
Head – OEM machined casting
Intake Valves – OEM 30.3 mm intake valves
Exhaust Valves – SUPERTECH +2.3 mm (25.2 mm) exhaust valves
Springs / Retainers – OEM valve springs and retainers
Guides – Specially designed valve guides
Valve Seals – Viton valve stem seals
Camshaft – CatCams 1302461 or 1302469 with ARP 2000 sprocket bolt
Head Fasteners – ARP 2000 studs
Lifters – OEM hydraulic lifters
Valve Job – Custom multi-angle valve job for increased flow
Deck Surface – Resurfaced for MLS gasket compatibility