4R300 Rally Engine MINI R53 | R52 | Cooper S | JCW

TRACK-PROVEN PERFORMANCE
The 4R300 Rally engine is engineered for MINI Gen 1 drivers who demand maximum performance on the track. Whether you're competing in time attack, hill climb, or endurance racing, the 4R300 is designed to operate reliably under extreme conditions, far beyond the capabilities of a stock or mildly upgraded engine.
Built as a direct-fit replacement for the MINI Gen 1 platform, each 4R300 engine comes fully assembled, from oil sump to rocker cover, and is prepared for seamless installation into your high-performance build. When paired with our Engine Installation Package, it becomes a true plug-and-play solution, ready to deliver uncompromising speed and durability on race day.

FORGED TO COMPETE
The 4R300 engine is developed for serious performance builds, offering a fully forged bottom end capable of supporting up to 300 BHP in demanding motorsport conditions. At its core is a carefully inspected bare cast block, precisely machined to accept 77.25 mm forged Wössner pistons, purpose-built to handle high boost levels and elevated cylinder pressures. The rotating assembly features a factory OEM crankshaft, paired with race-grade Bridgeway H-beam forged connecting rods fitted with ARP 2000 bolts for maximum strength under load. KING race-spec bearings are used throughout to ensure durability where standard components fall short. A brand-new OEM-quality oil pump completes the bottom end, delivering consistent oil pressure under sustained high-RPM operation.

The block is then matched to our fully ported 4R300 Cylinder Head, based on an OEM casting and upgraded to accept single-groove SUPERTECH valvetrain components. These include +1.8 mm oversized intake valves, +2.3 mm oversized exhaust valves, and a complete beehive spring kit with lightweight titanium retainers. ARP 2000 head studs provide superior clamping force, ensuring a secure and reliable seal between the head and block, critical for high-boost applications.
During final assembly, the engine is equipped with a brand-new timing system, including chain, guides, tensioner, and timing gears, and is finished using all-new gaskets, seals, and essential fasteners to guarantee long-term reliability under track conditions.

4R300 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 is carefully inspected and machined if necessary to 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.

BUILT TO COMPETE
The 4R300 short block is developed as a high-performance upgrade for serious track and competition builds. It features the same forged 77.25 mm Wössner pistons used in our other packages, but is reinforced with a set of Bridgeway or K1 forged H-beam connecting rods fitted with ARP 2000 bolts, providing exceptional strength under high boost and elevated RPM. The OEM crankshaft is retained and paired with KING race-spec bearings to handle increased cylinder pressures and extended high-load operation. These enhancements ensure the 4R300 short block delivers the durability and performance needed for demanding motorsport environments.

4R300 CYLINDER HEAD SECTION

COMPETITION-SPEC UPGRADE
The 4R300 cylinder head is engineered as a high-performance upgrade for MINI Gen 1 engines built for track and competition use. Whether you're assembling a high-boost circuit engine or upgrading an existing build, the 4R300 head offers a substantial increase in airflow and durability over the 4R250 unit. Built from an inspected OEM casting and fully assembled with premium SUPERTECH valvetrain components, including oversized valves and lightweight retainers, it’s a purpose-built solution for extracting maximum performance at high RPM. When paired with our 4R300 short block, this head completes a race-ready package designed to compete at the highest level.

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 spec-designed manganese bronze Ultraflow guides, engineered for optimal heat transfer and shaped to improve airflow without compromising valve support. Each guide is precision-honed to ensure the correct valve-to-guide clearance, promoting proper lubrication and long-term reliability. The intake and exhaust sides are both significantly upgraded using oversized SUPERTECH valves, +1.8 mm on the intake and +2.3 mm on the exhaust. To support the larger valves, all seats are cut with a custom multi-angle profile for maximum flow, and both intake and exhaust ports are fully ported to enhance velocity, volume, and overall breathing efficiency.
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 4R300 cylinder heads are assembled using a full suite of high-performance SUPERTECH valvetrain components. +1.8 mm oversized (32 mm) intake valves are paired with +2.3 mm oversized (25.2 mm) exhaust valves to maximize flow capacity at high RPM. Beehive valve springs with lightweight titanium retainers and single-groove keepers are used to ensure stable valve control under sustained high-load and high-RPM conditions. Viton valve stem seals are fitted to guarantee long-term oil control and durability.

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.

THE CHAMBER MODIFICATION
All 4R300 cylinder heads feature reshaped combustion chambers as part of the porting process. This refinement removes sharp edges and casting irregularities that could create hot spots, reducing the risk of detonation and pre-ignition under high load. The area around the valves is also smoothed and blended to eliminate flow disruptions, improving low-lift flow and overall combustion efficiency.

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 4R300 engine is engineered to support power outputs of up to 300 BHP when paired with the appropriate supporting modifications, such as smaller supercharger pulleys, larger injectors, improved intercooling, colder intake air, and better-flowing exhaust systems.

WHAT’S IN IT

Short Block
Block – OEM machined casting
Pistons – 77.25 mm oversized Wössner forged pistons
Crankshaft – OEM crankshaft
Connecting Rods – Bridgeway forged H-beam rods 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 – SUPERTECH +1.8 mm (32 mm) oversized intake valves
Exhaust Valves – SUPERTECH +2.3 mm (25.2 mm) oversized exhaust valves
Springs / Retainers – SUPERTECH beehive spring kit with titanium retainers
Valve Locks – SUPERTECH single-groove collets
Guides – 4REVISION Ultraflow manganese bronze valve guides
Valve Seals – Viton valve stem seals
Camshaft – CatCams 1302469
Lifters – OEM hydraulic lifters
Valve Job – Custom multi-angle valve job for increased flow
Deck Surface – Resurfaced for MLS gasket compatibility