EFR 6258 Steel Supercore Turbocharger

£1,372.44 inc. VAT

Available to order — usually ships in under 7 weeks

Note this is a super core – no turbine housing

The Borg-Warner EFR6258 is just about the ultimate turbo for a Mazda MX-5, featuring some of the latest and greatest technology. The team behind the EFR program are motorsports and engineering enthusiasts through and through and this product line existing for motorsport purposes is purely down to their skunkworks team and the drive to make the best product for all motorsport disciplines.

“The First Two Cars to Receive EFR Turbos Were the Author’s Porsche 911 and Fellow Employee Doug Erber’s Mazda Miata. Accelerating our Product Observations Through the Installation Process Was a Key Early Step in the Program, Leading to Mid-Stream Improvements. ”

You can read more about the development process and detail around the finished product here; efr_technical_training_book

Able to produce 350bhp with relative ease on a forged 1.8 BP / MX-5 Engine using stock cams on pump fuel (99) thanks to its incredibly efficient turbine wheel high compression engines (10:1) can also be used with relative ease, requiring less boost to make the same power numbers as well as faster spool up.

Compressor Specifications

  • Compressor Type:?Forged-Milled Wheel (FMW) Extended Tip
  • Compressor Wheel OD (exducer):?62mm
  • Compressor Wheel Inducer:?49.6mm
  • Max Flow Rate: 44 lb/min (440bhp potential)
  • Built-in Recirculated BOV:?Improve response on throttle transitions
  • Compressor Housing: 2.5″ inlet, 2.0″ hose coupler outlet.

Turbine Specifications

  • Turbine type:?Low Inertia Gamma-Ti Turbine Wheel
  • Turbine Wheel OD: 58mm
  • Stainless Steel Investment Cast Housing
  • 0.64 A/R T25 Housing (Internal WG)
  • 0.80 A/R T4 Twin Scroll Housing (Internal WG)
  • Turbine outlet:?GT-Vband (aka small 3″ vband) ~92mm OD for all EFR turbos


  • Dual Row Ceramic Ball Bearings – lowest friction and fastest spool/response, most extreme durability, built-in oil control orifice – (aka oil restrictor)
  • Watercooled Center Section – water cooling is recommended, 14mm banjo bolts
  • Double seals on both turbine and compressor end for extreme durability and resistance to any oil seepage
  • Boost Control Solenoid Valve Integrated to Compressor Housing
  • Integrated Speed Sensor mounting provisions
  • Capable of 3.6 Pressure Ratio or 37PSI of Boost

Compressor Map

BOFI Tuning Recommendations / Notes

On an optimized setup, we would expect a maximum BHP of 410-430 at around 26-27psi of boost pressure. You will need an oversized intercooler, an efficient engine with camshafts that can rev out to ~ 7400rpm or so. This turbo has produced around 420BHP on E85 on DynoJet Chassis Dynos, this is around the upper limit of the turbos flow potential.

At circa 18psi on a 10:1 rod block engine, this turbo can make 340-350bhp on a stock head on pump fuel. Mileage may vary depending on intake and exhaust setup. This is right in the meat of the efficiency band of the turbo.

See it in action here;

Additional information

Shipping Weight 9.5 kg
Shipping Dimensions 37 × 33 × 37 cm




Country of Origin



Mk1 (89-98), Mk2 (98-05), Mk3 (05-15), Mk4 (15-24)

Warranty information

Warranties cover defects in materials and workmanship only. Warranty is for replacement of a similar product, repair of the original product or refund of the purchase value only and excludes all labour and incurred charges including towing, fitting, inconvenience, and purchases of other manufacturer's products. The warranty is good for the period stated in the additional info tab from the date of purchase. Mileage warranties are for road use only and proof of mileage is required. Products must be installed by an independent experienced professional mechanic and the suspected defect must be present at the outset. The warranty does not cover damage caused by incorrect installation, failure to comply with the maintenance requirements of the vehicle, processing or otherwise changing the product, ordinary wear and tear, or any other external influences. Warranties are invalid if the product is used for racing, rallying, drifting, track days or any other form of motorsport or competition. Please refer to the manufacturer's own warranty documentation for more information.

Making a warranty claim

Proof of purchase receipt showing the date of purchase, proof of mileage at installation, proof of current mileage and invoice of the work undertaken by an independent experienced professional mechanic must be supplied along with the returned products for a warranty claim to be considered. If your vehicle needs to be used whilst your warranty claim is considered replacement parts from the same manufacturer should be purchased through BOFI Racing. In the event of a successful warranty claim, we will refund the card that was originally used to purchase the replacement parts, in full or in part depending on the nature of the claim. BOFI Racing reserves the right to make full or partial compensation at its sole discretion depending on the condition and mileage use of the returned suspect parts. For example, if you have used the part for several thousand miles before a defect is noticed, only partial compensation may be offered.

Make Model Year