OMEGA FORGED PISTONS 73.5mm - SHORT HEIGHT

For forged Omega pistons we would recommend a skirt clearance of 0.004". The largest diameter of the piston should measured with a micrometer, 90-degrees to the gudgeon pin, three quarters of the way down the skirt. The recommended ring gap (top and second ring only) is 0.010-0.012".

Yes, we suggest plateau honing with a cross hatch angle of 35-40 degrees. After honing with either conventional (#220 - #280 grit) or diamond stone (#325 - #550 grit), finish by smoothing the surface with a fine-grit conventional abrasive (#400 - #600 grit) or sweep the bores with a flexible brush or a nylon bristle plateau honing tool. This is necessary to get rid of jagged peaks and folded and torn material. Your machine shop may have different preferences.

These are designed to fit with a bushed 18mm little end diameter in a fully floating setup, whether that's an aftermarket steel conrod or a standard conrod modified with a set of MED-1018-LB bushes. Ideally these are paired with 6" long conrods, or else you will need to machine a large amount from the top of the block to achieve a suitable deck clearance with standard 5.750" conrods. This can lead to further complications such as pushrod length and rocker geometry setup.

Rather than being fixed in place, the gudgeon pins can move and rotate in the conrod little ends, with the piston held to the pin by a pair of wire clips. The fully-floating setup is preferred by race engine builders for ease of assembly/disassembly, while there is also less chance of damaging the pistons on assembly.

The pistons are only one part of the equation, so it would be inaccurate to supply a static compression ratio figure without knowing more information on the engine build. If you can email us with the cylinder head chamber volume, head gasket type and the deck clearance figures, we will be able to calculate this for you, and make further recommendations.

It depends - these are predominantly used in competition A-Series engines, where the higher operating temperatures give a greater expansion rate. As such, they will run marginally larger bore clearance to our range of Omega diecast pistons. If the engine is built to a similar spec to a competition engine then it will be absolutely ideal on forged pistons. For more mild engines you may prefer to look at our range of diecast pistons instead.

Weight - these are considerably lighter than an equivalent diecast piston, as more material can safely be removed as part of the intricate machining operations. The additional strength allows for the use of a lightweight 18mm gudgeon pin, itself saving 29g a piece compared to the 13/16" standard diameter pin. For any high RPM A-Series engine, saving weight is vital. These are also better suited to compression ratios over 11:1.

The weight will vary depending on your chosen spec. As an approximate guide, including the ring pack and gudgeon pin, single piston weights are as follows: 1.248" flat top, 299g, 1.248" 7cc, 272g, 1.115" 7cc, 266g. Each boxed set is weight matched within 0.5g. The piston weight may vary from one production batch to another, so please contact us at the time of order for the most accurate measurement.