25-07-2012, 02:27 PM
The theory is that they'd be a better engine, however in reality, the 12v design was simply an emissions thing more than a power thing... They over complicated the head design with hydraulic lifters, which is one of the XUD9s main plus points (60psi at the manifold before any valve spring issues - and they tend to keep their clearances quite well considering how many they'll do without needing adjustment...)
I've seriously been looking at it as an option recently since I'm changing my engine, but it's not worth the hassle and ballache to change to when there's other parts that will more than likely cause issues when pushing for more power... Remembering also the 96mm crank will reduce it's happiness to spin fast, you send the mean piston speed up even more, combined with the fact you've got 85mm pistons, more weight on the end of the conrod, accelerating and decelerating to and from higher speeds, when they're VERY heavy piston/rod assemblies as they are...
240hp has been seen a few times with indirect injection engines with less capacity than ours... Displacement is nothing without better volumetric efficiency...
Say our engines are 75%VE at peak, not including boost... That gives us an actual displacement of around 1430cc...
Say the 2.1 ALSO is 75%VE at peak, excluding boost... That gives us an actual displacement of around 1566cc...
If we could bump that on an 8v 1.9 to 85% - you've already bumped that to 1619cc...
Then consider that possibly the 2.1 heads in reality don't flow as well... By the time you've finished getting a 2.1 in, you're nearing what you could have done by just improving head flow on the 8v 1.9... but you've got all the issues of the 2.1...
I'm no expert in head porting or head flow, but that's how I see it anyway...
I've seriously been looking at it as an option recently since I'm changing my engine, but it's not worth the hassle and ballache to change to when there's other parts that will more than likely cause issues when pushing for more power... Remembering also the 96mm crank will reduce it's happiness to spin fast, you send the mean piston speed up even more, combined with the fact you've got 85mm pistons, more weight on the end of the conrod, accelerating and decelerating to and from higher speeds, when they're VERY heavy piston/rod assemblies as they are...
240hp has been seen a few times with indirect injection engines with less capacity than ours... Displacement is nothing without better volumetric efficiency...
Say our engines are 75%VE at peak, not including boost... That gives us an actual displacement of around 1430cc...
Say the 2.1 ALSO is 75%VE at peak, excluding boost... That gives us an actual displacement of around 1566cc...
If we could bump that on an 8v 1.9 to 85% - you've already bumped that to 1619cc...
Then consider that possibly the 2.1 heads in reality don't flow as well... By the time you've finished getting a 2.1 in, you're nearing what you could have done by just improving head flow on the 8v 1.9... but you've got all the issues of the 2.1...
I'm no expert in head porting or head flow, but that's how I see it anyway...
