ENGINE INTERNALS
The OEM internals of a YB are actually very good, especially the stock cast steel rods (much better than most OEM cast iron rods) which have been proven to cope with 500bhp – the only criticism is that they are a bit on the short side. Therefore, to free up a bit more power (as much as 8-10 bhp in some cases), many tuners opt to fit longer rods – usually 136 mm as opposed to the standard 128 mm items.
Doing so makes the rod angle more favourable – meaning that when the crank rotates the rod doesn’t travel through such a steep angle and isn’t trying to be forced out of the cylinder wall, but is instead being pushed upwards.
The stock crankshaft is also very capable as standard – it can cope with most things thrown at it and is only really changed when stroking the engine to a larger displacement. There is one caveat though – if it has been ground down a size or two it’s only really suited to sub-350 bhp applications, and with the prices of non-ground cranks on the rise, the price gap to a new aftermarket item (like the Farndon crank available from Burton Power at less than £1500) is ever decreasing.
The pistons are particularly well engineered as standard, and have been proven to work well on 400 bhp engines many times over. However, when altering the compression ratio or using valve cut-outs (needed for engines running anything more aggressive than BD10 cams) the machining costs in addition to the £120-per-piston can add up, and will cost roughly the same as a set of forged items, so naturally many engine builders opt for this instead.
On the subject of compression ratios 7.5:1 and 7.2:1 used to be the norm in high boost applications, but with the advent of better engine management, improved gasket designs, and greater clamping force offered by stud-and-nut kits many tuners are taking advantage of this to maintain a higher compression ratio – in some cases actually increasing it from the standard 8.0:1 to over 9.0:1!
“THE STANDARD INTERNALS OF A YB ARE ACTUALLY VERY GOOD, ESPECIALLY THE CAST STEEL RODS”