PS750 on a N55E, anyone else with this?

[JPuehl]

I'm trying to figure out what the capabilities are of the PS750 for the N55E PWG. I notice a a tune where I'm targeting 28#, in 4th gear at 6000 RPM at 94.4% WGDC boost starts tapering down from 28# ending up at 24.4# at 6750 RPM at the same WGDC, and I know a flat WGDC will cause boost to decrease but it's already at ~95%. In a tune where I had 100% WGDC from ~5750 RPM on, boost still started dropping at 6250 RPM. Does anyone know how much boost this turbo should be capable of for this platform?

I have tested everything to make sure nothing is not functioning correctly as listed below.

Boost leak test: pumped up 35# on the inlet of the turbo and only slowly leaked pressure after releasing the air hose.

Pure HDWGA: Used a MityVac on the line going to the WGA, cranked up 20 inhg and over the course of about 22 minutes lost ~2 inhg, so not bad.

Valve cover: Used a MityVac connected to the port feeding the boost solenoid, cranked up 20
inhg and over the course of 20 minutes lost 0 inhg.

Boost solenoid: Used a MityVac in the VAC inlet port, cranked up 20 inhg and lost about 1.5 inhg over the course of about 20 minutes.

Tested that the WGA was actually going to full close: Made a CWG tune with the CWG table at 100 for the entire table. Flashed and idled the car, MHD showed 100 WGDC, I got under the car and marked the shaft right at the WGA housing. Shut the car off, connected the MityVac to the WGA line again, cranked up 20 inhg and the shaft was in the same position as when the car was running using its own vacuum.

I have another Pure HDWGA on a shelf in the garage that I'll swap out to verify I'm getting the full range of motion on that.

 

[wheela]

Not sure how much preturbine back pressure you get with 24.4 psi boost at 6750 rpm, but I bet its somewhat higher than your boost pressure. 20 inHg may not be enough to hold the flap closed against that much back pressure? It would be intersting to see what boost the f-chassis guys can hold on the P750 with their electronic wastegate actuators.

 

[wheela]

Do you have any way of mounting a camera to record a video of the actuator rod during a pull?

 

[valpfrmnc]

JPuehl its your backpressure 100%. Wastegate is forced open as your EMAP is not 1:1 but probably 1:1.5 or higher. What you need is a proper wastegate setup and solenoid to control. Hit me up on instagram pw_performanceaz so i can explain or give me a call. Number is in the bio.

 

[valpfrmnc]

I am running 32 psi till redline btw.

 

[JPuehl]

JPuehl its your backpressure 100%. Wastegate is forced open as your EMAP is not 1:1 but probably 1:1.5 or higher. What you need is a proper wastegate setup and solenoid to control. Hit me up on instagram pw_performanceaz so i can explain or give me a call. Number is in the bio.

My IG account was disabled from lack of use so I'll need a different way to contact you, lol

 

[wheela]

Seems like spoolstreet may be a good place to share with the community

 

[valpfrmnc]

Wheela i am willing to share but only to a certain extend. Some things you only figure out by studying, learning and years of experience and its simply business. I shared already enough with JPuehl to get him going . Appreciate all the help.

 

[wheela]

Wheela i am willing to share but only to a certain extend. Some things you only figure out by studying, learning and years of experience and its simply business. I shared already enough with JPuehl to get him going . Appreciate all the help.

Fair enough

 

[wheela]

Since I've been looking into and testing options for controlling conventional pressure based wastegates directly from the DME, I'll share my learnings here. I've shared this already in my build thread, but since that's slow going, and it's buried 11 pages into the thread, I'll copy it here for easy reference.

 

[wheela]

Here's some initial testing I did using a Pierburg 7.01024.00 boost solenoid. I initially tested this valve based on promising feedback from hardparker's thread.

expand...

So, I finally got around to testing this boost solenoid at a higher duty cycle frequency.

But first, I tried a baseline test at the 32Hz duty cycle frequency (what the valve was designed for). With about 23 psi supply pressure, It worked as expected. From 100% to 81% WGDC, the wastegate was fully closed with no boost pressure hitting the wastegate. Reducing from 81% WGDC gradually sent more pressure to the wastegate. By 30% WGDC, pressure in the wastegate had reached about 14psi, at which point the gate started to open (it had a 14psi spring, so it was nice to see the results align). Continuing to reduce WGDC gradually opened the gate further until at 13% WGDC the gate was fully open, with full boost pressure (about 23psi) holding open the gate. This would allow for a good range of wastegate positions, and varying boost force on the gate by varying duty cycle.

Testing at high frequency:
At duty cycle frequencies above around 100Hz, the valve fell on its face. It essentially turned into an on/off switch. There was no gradual transition or pressure control to the wastegate, beyond all or nothing. At high duty cycles, the gate was closed, with no pressure sent to the gate. As duty cycle decreased, pressure sent to the gate was relatively unchanged, until some point, the valve transitioned and sent all pressure to the gate, and it would fully open. And then increasing WGDC back up, there was a lot of hysteresis, as you needed a higher WGDC% to get the gate to transition back to closed than was needed for it to open.

So. I'm not liking how this valve performs under the high duty cycle frequency range our DME runs in. I'll be sourcing some different valves to test to see if I can find one that seems to work better at the 250Hz range.

Attached are some pics of the setup, and some videos of testing at 32Hz and 200Hz.

Testing at 32 Hz:

Testing at 200 Hz:

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[wheela]

 

[wheela]

I've been reading about the stock pressure converter and how it works. Attached is some information about them. In summary, they have a diaphragm with vacuum on one side, and vent to atmosphere on the other. Vacuum level is controlled by balancing the pressure differential on the diaphragm against the magnetic force from the solenoid (which increases with duty cycle).

So I've been thinking if these work by the magnetic field pulling the diaphragm away from the vacuum from the vacuum supply, it should work just as well if the vacuum supply was vented to atmosphere, and the vent was instead connected to boost pressure - at least up to around 14psi (because the pressure differential across the diapgram would be the same magnitude, and in the same direction as its intended use condition). And obviously, it's designed to work on out stock 250Hz duty cycle frequency

However, our stock pressure converter doesn't have a port on its vent, it has a built in filter to keep crap from getting pulled in when vacuum is released. So I perused for a Pierburg pressure converter that had a barb connection on the vent, and the same style electrical connector. I found Pierburg valve 7.21903.70.0.

 

[wheela]

I tested this valve by connecting the boost supply to the valve's vent, and venting the valve's vac port. And it works!!! This will allow external wastegate control by the DME with no external boost controllers required!!

Usable duty cycle range is about 15% to 100%. It's pressure output is quite linear between 15% and 100% duty cycle. At 100% duty cycle, it reduces boost pressure by around 13.5 psi or so. Should be plenty to work with either the 10 psi or 12 psi wastegate springs I'm considering using.

I still have some details to work out - since it's only rated for vacuum (worst case pressure differential across the diaphram of about 14.7 psi) I don't know how much over-pressure it will handle in my configuration. So I'll incorporate either some kind of regulator upstream of it, or a relief valve after an orifice in the boost line venting back to the intake to keep boost pressure hitting the valve below a 14-15 psi.

Attached are some videos of it in action, as well as pressure output vs. duty cycle graphs I made at various boost (supply) pressures from my air compressor.

 

[wheela]

Videos:

12psi supply pressure

14psi supply pressure

 

[wheela]

The Pierburg vacuum transducer that worked above actually seemed to be intended for an Audi throttle body. I'm not sure if this valve has as large of an orifice as a unit designed for a wastegate, so I kept looking.

Since then, I've found a version of an n75 Pierburg vacuum solenoid for VW wastegates with the same electrical connector as our stock pressure converter. It's Pierburg 7.21903.75. I have the valve in-hand, but haven't had a chance to test it yet.

 

[wheela]

Also regarding duty cycle frequency, I've found the range from low (32-ish Hz) to high (200 to 1000-ish Hz) is needed depending on the type of solenoid valve being used.

The high frequency is for proportional position control solenoid valves, which control the valve to an infinitely variable position based on duty cycle vs. standard (on/off, or digital) solenoid valves, which are either fully open or fully closed a percentage of time based on duty cycle. Here's a good description of the two types:

PWM Solenoid Theory | TLX Technologies

Pulse Width Modulation Solenoid operation uses a DC supply voltage that is switched on and off at a given frequency for a modulated period of time (duty cycle).

www.tlxtech.com

Our stock pressure converters fall into the proportional category, which is why they need a higher duty cycle frequency to work properly. Attached is a PDF I found with a really good description of how our pressure converters work. It's much different than a Mac valve.

 

[wheela]

@JPuehl have you looked into this electronic wastegate controller from full race? It takes the duty cycle output from the DME as and input and controls position of standard electronic wastegate actuators. I called the company that makes these for full race a while back and they said it should work with bmw 300Hz duty cycle frequency.

Electronic Internal Wastegate Controller by DCCDpro

The Full-Race EWG-Pro by DCCDpro is a dedicated Electronic Internal Wastegate controller for use with Full-Race eIWG Electronic Boost Control Conversion Kits or MHI / Melco Actuators. The fully programmable interface supports 5%-95% Duty Cycles for superior boost control.

www.full-race.com

I seriously considered going this route with an internally gated EFR. But I chickened out because it would go on my daily driver, and I was paranoid that if the controller ever broke down on me, I may or may not be able to get a replacement depending if that company is still around.