LAracer

Hi guys - another altitude question

The stock ecu "controls" boost based on absolute pressure, right? So 10psi is stock boost pressure based on see level ambient pressure. Thus, up here at 7000ft, since ambient pressure is 3-4psi lower, my boost gauge (which reads pressure relative to my ambient pressure and not relative to sea level ambient pressure) should read 13-14psi for stock boost levels, right?

This makes sense to me since 10psi at sea level and 13psi up here is the same absolute pressure.

Even though it makes sense, I installed manual boost controllers ("home depot") to lower the boost - lowest I can get with a smooth pattern is 11psi.

Now, if I'm wrong about this whole absolute pressure thing - if I should still be seeing 10psi on my boost gauge, even at 7000ft - then I'm running pretty close to the edge at 11psi on the stock ecu.

I just wanted any opinions on my situation. Am I safe or should I worry. I could get a PFC, but I think I'd need to get it tuned close to 7000ft for it to be right (and there's not many rotary tuners up here).

Thanks

rynberg

That should be right. The stock ecu reads absolute pressure, so if your atmosphere is really 3-4 psi less than sea level, you should be good to go at 13-14 psi.

This would also make sense as the wastegate actuator reacts to 7 psi of relative pressure = 11 psi in your case.

KevinK2

The wg will move based on pressure differential across the diaphram. 7 psi gage pressure will initiate opening, regardless of elevation.

Mazda Service Highlights lists fuel cut boost limit in terms of absolute pressure vs rpm, so seems logical ecu allows higher boost at elevation. I suspect the extra boost is more likely after transition.

LAracer

Thanks for the reassurance guys .

volley1

I think this helps me too. I am in Denver and have the same problem. Just did a run last night and saw 1.0 BAR on my new Greddy boost gauge . And then it transisitoned. That should be 14 psi and I didn't hit fuel cut. I thought I had a vacuum hose problem. Let me know if I am incorrect as I don't have the money to replace a blown engine right now.