Technical Pure Stage 2 on High Elevation altitude

ganque

Specialist
Jan 22, 2018
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BMW 135i N55 DCT pure stage 2
Hi Everyone,
So the PS2 turbo is known to have some issues on high boost targets, and I believe it also affects other hybrid or bigger turbos for N55 on the market.
Fact: High Elevation = Lower air density = less air getting into the cylinders

I was wondering what a realistic boost expectation was for the PS2. Im at 5000ft and the PS2 turbo is maxed out at 22 psi and tappers down to 18 ~ 19 psi.

If there are other people running this turbo at a high elevation and only making the same boost as me, then I will stop hunting for boost leaks. So far I've done 3 or 4 boost leak tests by pressurizing the intake tubing from the turbo intake feed. Already changed twice the intercooler couplers with t-clamps, boost solenoid is brand new, etc. WGDC is still maxed out to 100% above 5000 RPM.

I would like to hear from other people, maybe people from Colorado who have similar elevation levels as I do here in Guadalajara, Mexico.

Thanks in advance,
Ganque
 

doodlebro

Specialist
Nov 23, 2018
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I just got through 4 months of headaches trying to figure out why I was not hitting targets on my PS2. Last night I noticed that the vacuum line from my exhaust flap was disconnected, causing a pretty significant leak and rendering my PCV system ineffective. After connecting it I was able to hit targets with a much more reasonable taper. So check your vacuum lines and make sure that's not it.

I am in Denver so 5-6K in elevation, although my target is only 16 PSI. I know that I have no boost leaks as the last shop tested for them up to 21 PSI. This should be the first thing you verify, as 100% WGDC at 5K RPM surely points to a boost leak. To hit my target tapering down to 13 at redline, my WGDC gets to 70% at the highest. I also overboost to 17-18 on tip in, so clearly there is a lot of room.

Ambient pressure here is around -2.5 PSI, which you have to take into account. Given that these turbos max at around 25 or so PSI at sea level, 22-23 seems like a reasonable peak given the lower density air.
 
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Twisted Tuning

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Oct 25, 2016
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N54 and N55 Cars
COnsidering at sea level the PS2 is on average good for 22-24psi up top. I'd say you're doing very good at 19psi at your elevation @ganque . But take care overspinning the turbo up that high. Because to make that 19psi you're probably working it harder than the 22-24psi at sea level.
 

F10_254

New Member
Jan 6, 2024
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Really happy I stumbled on this chat... So I have same issue at 5500ft elevation maxing out at 20psi 100WGDC...same bosst also at 70%WGDC tapering to 16psi high RPM (NOT SURE WHY) at times always thinking I have significant leak but could be maXING OUT PS2 TURBO on my F10 N55 ☹️ is this normal?
 

pbondar

Sergeant
May 30, 2020
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In aviation we get used to density altitude calculations as you can imagine by the time a piston engine gets to 18,000 ft it’s really wheezing.

All turbo’d piston aircraft engines suffer the same fate..the point at which you can’t maintain them expected boost is the critical altitude.

Even at 5k you’ve lost 2.5-4.5 psi depending on height and temp.

So it looks like you’ve just run out of puff…

FWIW on automotive design based aircraft engines they replace the stock turbo with something of a truck to keep it blowing hard as the altitude increases..

Not that I’m a N55 expert..
 
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