Has anyone had their XUD chuck a HDI rod?

[Toms306]

If I've understood correctly, the XUD puts more 'instant' pressure on the piston (and rod) than the HDi. The Hdi reduces knock by having pre-injections and the knock sensor will also stop it knocking badly...with the XUD its just up to the person changing the fuelling. And surely pre-igniting puts massive strain on the rod as its still being pushed up by the crank as the explosion is trying to push it back down again.

Does that make sense? Just thinking that might be why HDi's don't seem to break rods even at the same sort of power increase?

If I'm completely wrong then fair enough lol.

There's no knock sensor, but essentially yes... There's no way of pre-igniting a diesel... Pre-ignition indicates an "uncontrolled" and "unwanted" burn of the fuel, Diesels will simply burn the fuel when you spray it in, if you spray it in at the wrong time, that's either too advanced or too retarded... You can't "pre-ignite"... Remember at full load at high RPMs, you'll be seeing the fuel going in near 15* BTDC!

Well, yes and no... Infact the peak pressure of a HDi for the same power level is actually probably higher, DIs burn their fuel quicker, when it goes in, it all goes off at once whereas IDI can get away with a much longer injection window since they've got a precup to keep the heat for continued combustion - something that a DI cannot do - you've got a mega short window in which to get the fuel in before the piston has dropped and that heat from the compression has disappeared.

Listen to a transit van vs an xud with regards to "clack" the XUD is much more muted, this is because it's not burning all the fuel in one massive clump...

However, the compression strain constantly applied to an XUD is what kills them, 21:1 compression ratio, 30lbs of boost, all the heat that goes with - it's all a recipe for causing mental high average cylinder pressures.

HOWEVER as previously pointed out, XUDs are at a disposition, I've seen STOCK ones with banana rods... There WAS a fault in the forging process that causes this, it's nothing to do with the fact that the engines as stock are strained more... If you put HDi rods in every stock DT out there, I rekon you'd near enough never see another random rod failure...

Ah ok, cheers for clearing that up Ruan.