Our customer had a normally aspirated Clio 1.6GT (similar to the one pictured – image © Renault UK) and wanted to fit a turbo kit to the car. Normally aspirated engines generally run to high a compression for a reliable turbo conversion, and would limit the amount of boost you can use.  Lowering the compression ratio to 9.0:1 would improve reliability and increase potential boost pressures and make more power.

The original Renault Clio 1.6GT piston was supplied as a sample to give us the basic data of compression height (CH), pin diameter, valve relief depth and angles.  Aftermarket steel conrods were being used so we checked the conrod width so we could allow sufficient clearance for the pin end on the finished pistons.

In order to manufacture the pistons to a specific Compression Ratio of 9.5:1 we needed the following information that our customer supplied for his engine.

Bore size: 79.50mm

Stroke:  80.50mm

Deck height / clearance*:  0.2mm below block face

Head gasket thickness:  1.09mm

Cylinder head chamber volume: 36.5cc

Compression ratio required: 9.0:1                        

The finished piston shows the change from the original high-compression piston with a raised dome/intruder to a lower compression of 9.0:1 with a flat bowl design.