Engine power according to CUNA

The engine power according to CUNA indicates the power of an internal combustion engine for motor vehicles according to the regulations of the Italian standard CUNA ( C ommissione U nificazione N ormalizzatione A utoveicolo).

Performance data according to DIN (German Institute for Standardization), SAE (Society of Automotive Engineers) or regulation R 85 of the ECE (Economic Commission for Europe) result in different values.

Comparison of the measurement methods for determining performance

Each standard prescribes different conditions for measuring performance . On the one hand, this applies to the engine equipment with or without ancillary or additional units, and on the other hand, environmental conditions such as air pressure and air temperature , which also have an impact on engine performance.

Various engine equipment

CUNA: measured power with all ancillary units ( fan , alternator , etc.) but without air filter and without complete exhaust system
DIN: measured power with all auxiliary units (fan, alternator, etc.) with air filter and vehicle exhaust system
SAE: measured power without auxiliary units, without air filter and without exhaust system - the specification of bhp (brake horse power) corresponds to the measurement according to SAE

Various external conditions

DIN: Measurement at 101.3 kPa air pressure and 20 ° C ambient temperature
SAE: Measurement at 99 kPa air pressure and 25 ° C ambient temperature

This comparison shows why the measured performance differs depending on the standard.

In addition to the (older) measurement methods mentioned, there are also those according to ECE regulation R 85 (99 kPa pressure of dry air and 25 ° C, specification in kW).

This results in the highest performance rating for the same engine with the measurement method according to SAE (bhp), followed by CUNA and DIN.

Trivia

Especially in the years 1950 to 1969, when the sales of automobiles began to boom and there was no standardization, the measurement method that gave the best value was often chosen in advertising brochures and other publications, especially for export models , i.e. SAE-PS (of course without an indication of this). In German-speaking countries there was a clear tendency to use DIN information. Foreign manufacturers nevertheless printed German brochures with information according to other standards.

Since the end of the 1960s, the representation of the performance with specification of the measurement method has become established. Unless otherwise noted, European manufacturers uniformly use the information according to ECE, with the side effect that during this time new models apparently had lower performance than their predecessors, but in reality only the performance specification was changed to the lower DIN measurement. Italian engine manufacturers also used the CUNA measurement method.

If, in older publications and brochures from automobile manufacturers, performance information that appears to be contradicting is often to be found, this is due to the different measurement methods.

The confusion can only be cleared by comparing German publications with other documents. German-language brochures from Switzerland or Austria often have higher information, which in turn is identical to Italian brochures (CUNA). Even higher information, especially in French and English brochures, allows the conclusion that SAE-PS were used.

Examples

A Fiat 850 Special from 1968 had 47 PS (34 kW) according to the CUNA standard and 45 PS (33 kW) according to the DIN standard
A Fiat 850 Sport Coupé of the 2nd series from 1968 or the 3rd series from 1970 had 54 PS (40 kW) according to the CUNA standard, 52 PS (38 kW) according to the DIN standard
A Fiat 127 of the 1st series from 1971 had 47 PS (34 kW) according to the CUNA standard, 45 PS (33 kW) according to the DIN standard

In the Fiat 130 from 1969 to 1977, on the other hand, measurements were always made according to the DIN standard and, depending on the series, 140 or 160 or 165 hp were specified accordingly.