Not so fast everyone...
Does boost change significantly at elevation?
Will it matter what ambient atmospheric pressure(elevation) the turbo is operating in as far as the waste gate is concerned?
Does Wastegate set point need to be changed to reach similar boost pressure at greater elevation than sea level?
Wastegate diaphragm is boost pressure dependent not atmospheric pressure dependent.
Wastegate opening is mostly determined by the spring in the wastegate diaphragm.
Its all about absolute pressure, not gauge pressure.
Wastegate runs on absolute pressure, not gauge pressure. Even when wastegate is set using a normal boost gauge(zero'
[email protected]_sea level atm)
example:
atmospheric pressure @ sea level 14.7psi
boost gauge
[email protected] set point @ sea level +15.0psi
total 'absolute' wastegate set point pressure =29.7psi
(not boost gauge pressure)
So the variables are atmospheric pressure and absolute boost pressure.
In the above example we must reach 29.7lbs absolute' to satisfy the wastegate set point. The turbo has to supply this additional "absolute pressure difference in order to satisfy the wastegate.
You won't be able to read this on your boost gauge because a boost gauge is zero'd out at atm 14.7. If we go to elevation and change our ambient ATM to 12.0 psi instead of sea level 14.7, then your turbo will have to make up that 2.7lb difference before you can even read 1lb of gauge boost. In other words your gauge is starting with a 2.7psi deficit compared to sea level. The same holds true for the wastegate spring opening pressure. IT does not change. Turbo has to and will, make up the deficit and will do it with a regular spring Diaphragm operated wastegate, and no other controller needed.
On a side note...
At some point in altitude the compressor(turbo) will reach max and not have the capacity to deliver the volume of air needed to reach set point of wastegate. This is
critical pressure altitude. But this doesn't seem to effect most rzr kits at elevations.The turbos used in most RZR kits are more than capable of supplying enough air at 8000' to reach normal 'absolute' boost limits.
The turbo has to work harder to keep the same boost as in lower altitudes. This means it runs at a higher pressure ratio, which creates more IAT…How does raising boost effect high elevation IAT ?
Engines need air mass, not volume, to operate. A non-intercooled RZR might run the same boost and volumetric efficiency (volume of air moved vs. displacement of the engine), but produces a lot less power than the same engine with intercooling. Higher temperatures make the air "thinner", which means you have less mass per volume (lower density), so the air mass entering the engine is lower.
Higher altitudes also make the air thinner (lower density), same effect as higher intake temps.
What I'm saying is 12 psi gauge boost is 12 psi gauge boost at any elevation. All our gauges are zero'd at 14.7 atm. We are not using absolute pressure controllers or gauges. All ours are zero'd at 14.7psi atm.
So no need to change anything. You might see it take more time to reach boost since the turbo is starting with a deficit. But that extra work the turbo compressor must make up, won't disappear no matter how you set the waste gate or boost.
opcorn:
