MrPotatoHead wrote: ↑07 Sep 2017, 14:09
gruntguru wrote: ↑07 Sep 2017, 08:19
MrPotatoHead wrote: ↑07 Sep 2017, 01:06
The valve "spring" pressure will likely be around the same as the v8 engines, if not higher, as the backside of the valve now has to resist the charge pressure pushing down trying to open the valves. You always have to increase valve spring pressure on a turbo engine.
I don't believe that is significant although it is a much touted "fact". Remember - although the manifolds (ex and in) have higher than atmospheric pressure, the cycle pressures throughout the engine are increased so it is likely the pressure drop across the valve is little different to NA.
It is a very real problem. Build some high PR turbo engines and you can run into it. It is has been seen on engine dynos using measuring equipment monitoring the valvetrain.
The problem is more about controlling the valve during the opening and closing events.
Very hard to say, untill we know exactly what type of friction it is. It could be piston/cylinder friction, it could be bearings, MGUH, compressor, turbo...
From all the problems seen with the PU I would put my money on piston/rings/cylinder friction definitely. The pistons are "sticking" under some circumstances. Thats why the PU broke in 2 halfs and so on.
5.3.1 Cylinder bore diameter must be 80mm (+/- 0.1mm)
5.14.1 Unless explicitly permitted for a specific application, the following materials
may not be used anywhere on the
power unit:
a) Magnesium based alloys.
b) Metal Matrix Composites (MMC’s).
c) Intermetallic materials.
d) Alloys containing more than 5% by weight of Iridium or Rhenium.
e) Copper based alloys containing more than 2.75% Beryllium.
f) Any other alloy class containing more than 0.25% Beryllium.
g) Tungsten base alloys.
h) Ceramics and ceramic matrix composites.
Finding the right materials can be a pain in the arse. With so many restrictions, it can be a gamble on finding the right alloy for the pistons, given the high compression . Basically the pistons have to "expand" at the very same rate as the cylinder at a change of temperature. If not, we see a waterfall of fluids flowing out of the car