These are the original Cosworth 90.335mm bore BDG piston PA0278, designed and manufactured by Cosworth, specifically for the modified Hoyle 1995cc BDG alloy rally block.
Cosworth forge these pistons in-house from 2618 high tensile strength aluminium alloy. The forge tool is designed specifically for this piston to give the best grain flow in the most highly stressed areas. Once forged, Cosworth then machine, inspect and pack the pistons.
Each set contains four Cosworth pistons, plus high strength gudgeon pins and clips along with high performance compression and oil control rings.
The PA0278 Cosworth BDG Hoyle piston comes with valve pocket cut-outs that are already machined.
The oil control ring groove includes an array of oil drain holes. Any oil that is scraped by the rings from the wall of the cylinder bore can drain back through these passageways into the crankcase or sump. These holes help to stop oil from building up behind the ring, which would otherwise find its way up past the rings and into the combustion chamber, creating unacceptable levels of oil burning.
The skirt shape is comprised of a smooth blended barrel form with an optimised profile specifically designed by Cosworth.
- Cylinder bore diameter = 90.335/90.348 mm
- Compression ratio = 11.7:1
- Compression height (distance from pin centreline to top of crown) = 33.485/33.535 mm
- Use with the long (5.23″ length) connecting rod.
- Gudgeon pin diameter =20.635/20.640 mm
- Small end width = 25.90 mm
- Ring widths = 1.00 mm top ring, 1.00 mm 2nd ring & 4.00 mm oil control ring