BMC Mini 998cc Engine Rebuild

BMC Mini 998cc Engine Rebuild

The brief with this engine was to tune to produce similar power to the 1275cc engine. The target figure was 60 bhp with 55 lb ft torque and with a young driver / owner our budget was very tight. Read below how we did it!


Crankshaft: Ground & balanced

Flywheel: Lightened & balanced

Conrods: Lightened & balanced with ARP rod bolts

Pistons: 998Std flat top – balanced

Cylinder Block: Refaced to bring pistons flush with the block face

Camshaft: Performance 285 set at 103 full lift, Single chain retained with offset key

Cylinder Head:

  • Inlet Ports¬†Slight polishing by seat area
  • Exhaust Ports Material removed throughout port area to match
  • LCB exhaust manifold
  • Hardened exhaust valve seat Inserts fitted + 3 angle seat cutting
  • Cylinder head reface – to achieve 11:1 compression ratio
  • Compression tested at 200psi
  • Standard rocker arm assembly
  • 12G295 casting , standard valves

Carb: Single 1 with good ram pipe

Wheels and Diff:?¬†The car came with 13″ wheels. Therefore a 3.9:1 diff was installed.


What a Fun Car! Its high compression and very light internals makes for a very responsive engine.

With a good torque value there are no flat spots. The power curve with HP is clean and achieves 8,000rpm very easily.

Mini Summary

Mini Torque Graph

Mini BHP Graph