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Two new specification values have been introduced to Carfolio.com specifications tables today. They are both derived values and relate to the performance and efficiency of the engine.

Firstly, brake mean effective pressure (bmep), an indication of the efficiency of an internal combustion engine, is calculated from the peak torque of the engine, and is expressed in both kilopascals (kPa) and pounds per square inch (psi). Bmep is always given for the peak torque rpm value. A good value for bmep for a naturally-aspirated petrol engine is around 200 psi. A couple of relatively modern cars with really good bmep values (for naturally aspirated petrol engines) are the 2008 Maserati GranTurismo S and the 2003 BMW M3 CSL, with 210.4 and 207.8 psi bmep respectively. For obvious reasons, values for turbocharged engines tend to be higher.

The next field that has been added to the database is the RAC rating. This is an ancient method for calculating horsepower, and for a (very) short time it was (somewhat) accurate in predicting the actual horsepower of an engine. It used a formula which theoretically could have produced an accurate value for horsepower, but it assumed certain variables to be fixed for all engines. As design, materials and technology improved, these variables deviated substantially from the generalised values used in the formula. The formula was used from about 1909, and in 1921 the UK Treasury used it to determine how much tax a vehicle was to be levied - hence the terms "taxable horsepower" and "Treasury rating". Whilst this formula was in force, from 1921 to 1947, it more or less dictated the trend of undersquare engine design, and also was the reason for the old model designations, for example the 1923 Alvis 12/50 SB - where the "12" was the taxable horsepower and the "50" the actual horsepower - the engine was making over 4 times that predicted by the already-obsolete RAC formula. This has been included for academic interest only.