Pistons

The pistons — nominal dia 86.5 mm — are provided with a combustion chamber approx. 17 mm deep (compression ratio e = 7.5 : 1 ).

The installation position is identified by an arrow punched into piston crown (pointing toward V-belt pulley).

The piston pin bore is offset from center by 1.5 mm.

The cylinder bores and piston dias are subdivided into 3 tolerance groups.

Tolerance Group Cylinder Bore Piston Dia ± 0.007

I 86.510 86.450

II 86.520 86.460

III 86.530 86.470

Porsche 924 Turbo Pistons

Piston ring assembly:

Groove I — rectangular compression ring 86.5 x 79.3 x 1.5 Groove 11 — baffle-taper compression ring 86.5 x 79.3 x 1.75 Groove III — chamfered oil ring 86.5 with expanding spring x 79 x 3

The turbo cylinder head has a combustion chamber which is approx. 4 mm deep. Unlike the normally aspirated engine, the spark plugs are located on the intake side.

Porsch924 Exhaust System

All the valves have positive rotators. The dimensions for stem length and OD of the exhaust valve head are changed.

Valve Dimensions:

Intake Valve a) 40 mm dia (40)

Exhaust Valve 36 mm dia (33) 8.95 mm (8.95) 133.35 mm (136.95) 45°

Note: The camshaft drive, the valve timing and clearance adjusting data are the same as the normally aspirated engine.

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