5.3 Power unit dimensions :
5.3.1 Cylinder bore diameter must be 80mm (+/- 0.1mm).
5.3.2 The crankshaft centre line must lie on the car centre line and 90mm (+/-0.5mm) above the reference plane. The power unit may only transmit torque to the gearbox by means of a single output shaft that must be co-axial with the crankshaft. The output shaft must rotate clockwise when viewed from the front of the car.
5.3.3 Valve stem diameter must not be less than 4.95mm.
5.3.4 All elements of the power unit specified in the relevant column of the table in Appendix 2 of these regulations must be installed in the union of the volumes that exist between two vertical planes normal to the car centre line separated by 700mm and in a box 150mm long, 250mm wide and 800mm high which lies symmetrically about the car centre line immediately ahead of the front vertical plane.
5.3.5 Power unit mountings may only comprise six M12 studs for connection to the survival cell and six M12 studs for connection to the transmission. All studs must be used and may be fitted on the survival cell, power unit or transmission. The installed end of the studs must be M12 and the free end may be a different diameter. The mounting faces of the studs for connection to the survival cell must lie on the forward of the two planes described in Article 5.3.4 and be located at Y215/Z15(2), Y340/Z260(2) and Y175/Z420(2). The mounting faces of the studs for connection to the transmission must lie on one vertical plane normal to the car centre line and be located at Y100/Z15(2), Y150/Z140(2) and Y255/Z345(2). A tolerance of +/- 0.2mm will be permitted on all of the above dimensions, all dimensions refer to the centre of the studs. The distance between the two planes is fixed at 480mm (+/-0.2mm). Any part which provides an additional load path from the survival cell to the gearbox, with a connection to the power unit, may only do so if this is incidental to its principal purpose.
5.3.6 The ES must be installed wholly within the survival cell.