Delica Canada | Mitsubishi Van Club

Can't help feeding this thread hijack!

I agree that 11 psi is 11 psi is 11 psi anywhere, but the 11 psi into the engine is pressurization being supplied by the turbo over and above ambient atmospheric pressure. Hence that 11 psi"g" description. Normally-aspirated engines still use air, they are just "pressurized" to zero psi(g)!

11 psig in Vancouver is 25.7 psia (a for Absolute)
11 psig in Calgary is 23.9 psia
11 psig in the vacuum of outer space is 11 psia

(When a tire goes "flat", it goes to 0 psig. There is still air in the tire, it is just at the same pressure as the local atmosphere; otherwise a flat tire would have a vacuum inside it).

So technically, that tire you filled with air to 30psi in Vancouver, you filled to 30 psig.

When you drive that 30psi(g)-Vancouver-filled tire to Calgary, I would expect a gauge stuck on it it to read 31.8 psi(g). It would have the same amount of molecules in it as it did in Vancouver, but the ambient atmospheric air pressure is lower, so the difference is made up on the gauge reading as a larger relative pressure.

That's why a turbo pressurizing a Calgary engine to 11 psi(g) isn't feeding in quite as many molecules of air/oxygen as a turbo pressurizing a Vancouver engine to 11 psi(g). The overall (absolute) pressure is still higher in Vancouver, even though the *increase* added in by the turbo is the same.

Gauges measure relative pressure (psig) not absolute (psia)

Excellent posts tonydca and Manitoba deli.

I knew the L400 must have a functioning wastegate like every other turbo system. So the Delica is like every other turbo diesel...you could lower the fuel slightly at high altitude to limit potential smoking mainly at idle for emmsisions reasons but you will still not ever increase power by doing so. Even though the Delica is a fine machine it cannot defy reality like Green1 seems to think it can.

The wastegate actuator which controls boost, is calibrated for sea level pressure, so when you take it to a higher altitude, it experiences a negative pressure on it, which the turbo makes up for with extra boost. it supplies the engine with the equivilant to 11psi at sea level. There would only be less air if it was recalibrated to 0psi at a higher altitude, then atmosphereic pressure would play a roll. Because most things (wastegate actuators, tire gauges, etc.) are calibrated to read zero at sea level, the pressures they read or achive are the same as at sea level, because you actualy are putting air in to "bring it up to zero" as if it were at sea level, and from then on the volumes are the same.

Jason

Manitoba deli wrote:The wastegate actuator which controls boost, is calibrated for sea level pressure, so when you take it to a higher altitude, it experiences a negative pressure on it, which the turbo makes up for with extra boost. it supplies the engine with the equivilant to 11psi at sea level. There would only be less air if it was recalibrated to 0psi at a higher altitude, then atmosphereic pressure would play a roll. Because most things (wastegate actuators, tire gauges, etc.) are calibrated to read zero at sea level, the pressures they read or achive are the same as at sea level, because you actualy are putting air in to "bring it up to zero" as if it were at sea level, and from then on the volumes are the same.

Jason

I wasn't aware of that - if the actuator diaphragm is a sealed unit on both sides, then I agree with you completely.

But if the one end (the end that the rod slides out of) is open to atmosphere, unsealed - which I thought it was - then the spring inside would be pushing against ambient atmospheric pressure, so the lower the outisde pressure, the easier it is for it to push.

I guess I am not explaining this correctly, because the spring side of the actuator is open to the air, so therefore my explination has been shot down hard. I do remember learning in Diesel Mechanics that turboed engines were not affected by altitude, but until I find my old books and explain this properly, with proof from the text book I will have to let tonydca take this round. Sorry to the original poster for helping hijack this thread. My wife isn't going to like it when I ask if she can help find my old text books. I'll start my own thread on this when I find my books.

Jason