ARP HEAD STUD FIXING KITS
( £108.33 EXC VAT )
The MED/Omega 73.5mm (2.894") short height die cast pistons are now even lighter than the original and are ideal for any A-Series engine from fast road to full race.
The 1.426" compression height can be useful alongside a long-stroke crankshaft, for when a block has been considerably decked or perhaps to lower the compression ratio.
See the Extra Info tab for more detail.
Do I need forged or die cast pistons?
The cost of producing a die-cast piston is considerably less than that of forgings, which is reflected in the price. Cast pistons weigh more than the equivalent forged pistons and are not quite as strong, so we have designed these to use a standard size gudgeon pin.
However, Omega cast pistons have been used very successfully for decades in all manner of A-Series engines, from daily drivers to competition cars. Do not confuse these pistons for standard factory-spec cast items - they are still a very high performance piston. As a general rule, opt for forged pistons if you wish to exceed 11:1 on the compression ratio, have a very high performance engine or wish to run high boost levels on a forced induction setup.
Which conrods should I use?
These are designed for use with standard conrods and are supplied with press-fit gudgeon pins. For high performance road and competition engines we'd highly recommend upgrading to the short pins and clips for a fully-floating setup and combining with a set of our MED steel conrods.
Floating pins or standard?
'Fully floating' refers to the gudgeon pin fitment to the conrod little end, where the little end is enlarged and bushed by a competant machine shop. Rather than being fixed in position, the gudgeon pin can still move/rotate freely in the bushed little end. The fully-floating setup is preferred by race engine builders for ease of assembly/disassembly. There is also far less chance of damaging the pistons on insertion.
Please note that we do not supply little end bushes for these standard 20.6mm (13/16") pins as every machine shop has its own preference on sizing.
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. We do not recommend a larger bore than 73.5mm for reliability and do not stock any pistons larger than this.
This process requires the melting of a special high-silicon alloy in an electric furnace with extremely closely controlled temperature. The molten alloy is then poured into a multi-piece die, producing a very accurately shaped piston casting.
The casting die is manufactured so that when the metal has solidified, the various pieces of the die can be extracted one by one. This means that undercuts and reliefs can be produced in the casting to reduce the piston weight.
Piston ring installation: