ARP HEAD STUD FIXING KITS
( £108.33 EXC VAT )
The Omega/MED forged lightweight piston is the lightest on the market. They come with a narrow-section ring pack, which will reduce friction, and the special ultra-light 18mm gudgeon pin. The pistons come complete with little end bushes to fit to standard-type conrods, to make the gudgeon pins fully floating (see Technical Downloads tab), along with special wire circlips to hold the pins in place. Alternatively, upgrade to our MED steel conrods for a direct fit.
Exclusive to MED - 73.5mm in standard 1.498" compression height with either a 7cc dish or flat top - see choices in the dropdown menu above.
With a standard 81.33mm stroke crank this will create 1380cc on a 1275 engine.
Why upgrade to forged pistons?
Our range of Omega forged pistons are stronger yet lighter than our diecast range, making them particularly well suited to higher performance applications. Forged pistons utilise a smaller, lighter 18mm gudgeon pin and bushes to convert the conrod little ends to a fully-floating configuration. Fully-floating pins give less chance of damaging the pistons on insertion, as with press-fit, and are easier to disassemble. Therefore it's the favourite method for competition engines.
Which conrods should I use?
For high performance road and competition engines we'd highly recommend using these with our MED steel conrods, as they come with an 18mm bushed little end specifically for these pistons. Standard conrods can be machined to accept the supplied bushes (see Technical Downloads tab).
What size pistons do I need?
Bore size remains one of the most common questions we're asked here at MED – should I go plus-0.020" for 1293cc or straight to 73.5mm for 1380cc? It's not as straightfoward as it first seems; you may be restricted by regulations to a set capacity, or the engine itself may have already been bored to a larger size. It may have even been bored, then re-linered again. In light of ever-increasing values of core 1275 engines, for cost-conscious engine builders we would recommend boring to the next size up where possible. A larger capacity should produce more power for a given engine spec, however, you may wish to keep a couple more bites of the cherry in hand, so to speak. Where maximum performance is the goal, 1380cc is the way to go.
The production of piston forgings is more complex than the casting process and some 80% of Omega's pistons are produced in this way. The main material used is RR58 (2618A). Two other alloys are used - one is a high silicon alloy and the other is a Metal Matrix Composite alloy.
The forging process requires material to be bought in at closely controlled diameters, this is then cut to billet size and all cut faces machined to a smooth finish. The billet is pre-heated in an air-circulating furnace to a temperature quite close to the operating temperature of the piston crown when the engine is operating at full power. This temperature is critical and cannot be disclosed.
This together with tightly controlled speed of the forging process gives a dense and very fine grain structure to the forging. Microstructure analysis of Omega's forgings and that of other manufacturers will highlight this difference. This fine grain structure gives the forgings higher strength and fatigue life. After forging, any excess material is removed and the forgings are then heat-treated followed by wet blast cleaning.
Tech info for conversion to fully-floating standard conrods:
Piston ring installation: