Quote:
Originally Posted by mycologist
Ok, sounds like a pretty good theory. The ECU pulls boost at higher elevation by the pressure compensation table. It is independent of whatever map you are running. It does this to keep the turbo in the area of the compressor map it wants to use (it has to spin faster to pump the thinner air up to the given boost level). Also, you have greater knock resistance at higher elevation I believe because the air is less dense. I know you can run somewhat lower octane safely at least. So you drive down a long ways and the learned values from high elevation are no longer applicable (because your hitting higher boost and your pushing denser air leaning you out), so the DAM goes down while it trys to sort things out.
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Nice, thanks. I was thinking along those lines (at least in the ballpark
) I just couldn't put it all together in a thought out coherent manner, as you just did.
I thought elevation probably had something to do with it, I just didn't know what exactly. Also, in the back of my mind I thought maybe elevation had nothing to do with anything since the maniford pressure is just relative to the outside atmospheric pressure anyway.
So here's another little tidbit for you guys: Usually when I'm down in the valley, I see peak boost of ~16.8 (map target is 15.8 +/- .5) which is an over boost of .5 psi. This past weekend I was down in San Fran and I hit 17.4 psi on one pull
. Do you think this was because the turbo/waste gate (ecu, really) hadn't yet "learned" that it can slow it's roll and still hit target boost in the dense sea level air? (also, in that particular instance the load was probably huge - 5 dudes in car, going up a slight incline, 3rd gear WOT)
Quote:
Originally Posted by mycologist
I've been biting my tongue but it has to be said - have you tried putting your finger in it?  |
I don't get it.