The Engine Number is stamped into the engine block. It is located on the edge of the front flange; where the engine meets the gearbox. It is to the right of the oil filter at the front of the engine. It will start with either C25XE or X25XE
Some late V6 Calibra's were fitted with the X25XE engine (short block only) from part way through 1997 onwards. The old C25 blocks were no longer being made so supplies were running out. Essentially almost identical blocks but the X25 has wider oil pathways (to support new flat base tappet type - not used in Calibra heads) and the oil pump now provides a hefty 20% increased output through use of a larger rotor. No matter which engine block type you have both types used exactly the same heads and inlet manifold for installation into the calibra engine bay; these were not changed.
The switch to the black "Ecotec" engine cover, or the inclusion of a secondary air injection system, is not necessarily an indicator of an X25XE engine number.
The X25XE, when installed in the calibra, continued to use the Motronic v2.8 ECU but marked with the identifier KC on the ECU case sticker. These late type Calibra X25XE ECU's included some minor changes to the EPROM code; what these changes were is unknown but a later (post 96/97) Tech 1 cartridge is required to correctly identify and communicate with the Motronic ECU.
The Motronic 2.8.1 ECU was reserved for use in the Omega X25XE/X30XE with functionality to support the dual/ram air intake system.
The Motronic 2.9 was made for Volkswagen and used to control the VW Golf and Corrrado V6's and is totally incompatible with the V6 Calibra.
An "R" stamped into the block after the engine number indicates that a replacement X25XE short block has been fitted by an official dealer after the car has left the factory (replacement engine).
V6 Calibra - Engine Number Meaning
C EC 91 / 441 / EEC (emissions control regulation rating) 25 Engine displacement in litres x 0.1 X Cylinder Compression Ratio (engines between 10:1 to 11.5:1) E Fuelling System (E = Fuel Injection) X 94 / 12 / EC (emissions control regulation rating) 25 Engine displacement in litres x 0.1 X Cylinder Compression Ratio (engines between 10:1 to 11.5:1) E Fuelling System (E = Fuel Injection)
Chassis Number Variants
Some modifications through the lifetime of the V6 calibra are described as being implemented on a "T" chassis. This single letter refers to the chassis body variant code and is placed towards the centre of the total VIN code.
Chassis numbers of "S" and earlier are often referred to as EARLY type Calibra's.
Chassis numbers of "T" and and later are often referred to as LATE type Calibra's
(note: there were no "U" chassis numbers because U can look like a V on a VIN stamp)
You can read the chassis number of your V6 from the bar code label stuck on the passenger side dashboard, from the VIN plate at the front of the engine bay or from the one stamped into the chassis under the flap of carpet between drivers seat and door frame.
this shows a late "V" type chassis number
notice that the chassis code letter is towards the centre of the VIN code.