Conventional pressure operated wastegates on the N55

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hardparker

Private
Jan 23, 2018
38
I'll preface this with saying that I live at a mile high altitude in the high desert of Albuquerque. While turbos kick ass over normally aspirated cars up here, the altitude and the summertime heat take its toll on the ability to make boost. It quickly revealed the deficiencies of the stock turbo and two generations of PS2s. My quest for more power and more boost has seen three turbos and killed both of those PS2s.

I think I have nine different wastegate actuators that fit and work to varying degrees for the N55. The iteration I'm presenting here is the simplest, most effective and most easily reproducible variant. I suspect it will work equally well on the N54, too.

The long and the short of it is that this setup works just like any other conventional pressure operated wastegate system. The DME controls it without difficulty. Tuning changes could be made to assist with quicker spool in comparison to the stock actuator and solenoid, but even without tuning and using a light wastegate spring, it works nicely.

Pros: More linear. Less peaky. More top end boost, especially with twin port setups. More aftermarket wastegate actuator choices.

Cons: Should be tuned. Can destroy your turbo if pushing too hard.

Parts I used:
Pierburg 7.01024.02.0 boost solenoid
Turbosmart Borg Warner EFR Twin Port B2 TS-0620-3143 wastegate actuator
6mm silicone vacuum tubing
1/8" NPT to hose barb fitting for boost source from charge pipe WMI bung.

I suspect other Pierburg solenoids that are similar and differ only in mounting style would work as well, but I can't say for sure, since I haven't tested them. A second easily sourced example might be the Volvo/Saab specific 7.22240.13.0. It mounts with a clip and has the same EV1 connector for plug and play ease. The modern Ford turbo solenoids also look like they could work.

I specifically chose the 7.01024.02.0 because it has a two hole mounting flange similar to the stock pressure converter and because the Syvecs and MoTech guys seem to use them fairly commonly. Also, I found reference in some technical documentation that said that the solenoid was meant to operate in the same 300 Hz range as the stock pressure converter. The standalone guys drive these closer to 20 to 30 Hz. Mac valves are driven at that frequency, too, which makes me wonder if they'd work if fitted with an EV1 connector. If the Mac solenoids work, the ideal combination would be a twin port wastegate and four-port solenoid.

I know that driving the solenoids at higher frequency effectively limits the range of usable duty cycle, potentially requiring re-tuning so that the effective passband of the solenoid is used. I used the solenoid at WGDC ranging from 30 to 90 steady state and peaking above and below that. I aimed my WG spring and tune combos to target 50-65% WGDC steady state for the most part, which seemed to work well. Lighter springs that required 80-90 WGDC for target boost with the solenoid seemed to work fairly well, too though. Without any scientific testing, I'd say the solenoid seems to have an adequately wide effective passband for our use but that the far top end above 80% yields little effective change in boost control, at least with a 5 psi spring.

The first actuator I used was a Forge Motorsports Sierra Cosworth FMACCOS4 actuator with the "7 to 10 lb" green spring. I had to change out the actuator rod, but fortunately Forge offers a good selection. I tested it to crack at 8 psi with my MightyVac. It yields 5 psi on the car when directly connected to the boost source with spring only pressure. The Turbosmart actuator tested to crack at 13 psi. It made 12 to 10 psi from peak in the midrange to taper at the top end, call it 11, on the car. Consider that all of my testing was at around 5,500 feet, and down -2.5 psi from sea level. Results at sea level might well make up that 2.5 psi deficit.

I chose the TurboSmart actuator since it was Borg Warner specific and twin port. With the N55 turbo's high exhaust backpressure, the twin port setup can more effectively combat the effects of autowastegating at higher engine speeds. The N55 autowastegates pretty badly above 5,500 RPM with the stock vacuum wastegate actuator. Altitude exacerbates that significantly due to lower available vacuum to hold the wastegate shut.

The twin port setup pressurizes both chambers of the wastegate actuator. The top chamber is connected to a boost source directly and will push against the spring to open the wastegate. The bottom chamber is modulated by the solenoid WGDC and effectively negates some or all of the attempts by the other chamber to open the wastegate. Pushing the valve shut helps combat autowastegating. It also helps improve spool.

When it comes to actuators, you can use whatever will fit. It needs a rod at least 6-3/8" long (7" is better) and threaded as M6 x 1.0mm. The Turbosmart TS-0620-3143 just barely works lengthwise after setting preload. The nut is right by the end of the shaft, but it works.

I did rudimentary electrical testing of the solenoids. The stock pressure converter solenoid measures 11.2 ohms while the Pierburg 7.01024.02.0 measures 23.2 ohms. This is a good thing, since it should draw less current than stock, so no fear of burning up the DME, and it should also have greater electromechanical damping factor and therefore better control of the solenoid. Especially useful at the 300 Hz drive frequency.

Anyhow, on to some results!

Map - Bootmod3 E30 PWG OTS
Actuator - Stock vacuum PWG actuator
Results - 16 psi peak @ 4,400, tapering to 12.2 psi at 6,000.
Log - http://www.bootmod3.net/log?id=5d31d617c090c678562893c1
attachment.png


Map - Wastegate spring pressure only
Actuator - Forge, green 8 psi springResults - makes 5 psi
Log - http://www.bootmod3.net/log?id=5d814f2ac090c658131401ce
attachment.png



Map - Bootmod3 E30 PWG OTS
Actuator - Forge 8 psi green spring
Results - 18 psi peak @4,600, 14.3 psi @ 6,000, 13 psi @ 6,500. Picked up 2 psi!
Log - http://www.bootmod3.net/log?id=5d87e5adc090c658e064ede2
attachment.png


Map - 90% WGDC test tune
Actuator - Forge 8 psi green spring
Results - 20 psi peak @ 4,000 with throttle closure, 14 psi @ 6,000, 13 psi @ 6,500
Log - http://www.bootmod3.net/log?id=5d83b845c090c6581314073b
attachment.png


Map - 100% WGDC test tune
Actuator - Forge 8 psi green spring
Results - 8 psi peak @ 4800, 13.7 psi @ 6,000
Log - http://www.bootmod3.net/log?id=5d83d9a1c090c6581314078d
attachment.png




The 5 psi spring in the Forge required 70% or better duty cycle to get close to target boost. It still showed some top end taper, but less than stock. Pushing the solenoid beyond 90% doesn't yield much increase in boost with this light of a spring.

Now for the Turbosmart actuator:

Map - Wastegate spring pressure only
Actuator - Turbosmart, single port
Results - 14 psi spring - makes 11 psi
Log - http://www.bootmod3.net/log?id=5d8921d7ae729b67235ff5da
attachment.png



Map - 65% WGDC test tune
Actuator - Turbosmart 14 psi spring, single port
Results - 22 psi @ 4,800, 17.6 @ 6,000, 16.6 @ 6,500
Log - http://www.bootmod3.net/log?id=5d8a781ec090c658e064f325
attachment.png



The 14 psi spring in the Turbosmart required 65% duty cycle, overboosted a little to about 21 in the midrange and was hitting my desired boost of 18 psi at 6,000 and 17 psi at 6,500. The overall boost curve was flatter and it pulled like a beast. Enough so that it started to sag my XDI 35 HPFP with E35 in the tank. Not enough to be noticeable while driving, but apparent in the logs when I'd bothered to log it.

The next steps for testing were to try a 12 psi spring combo and the OTS E30 tune. After that, down to a 7 psi spring in twin port mode. But, then this happened while I was beating up on it getting logs for about an hour. The PS2 chucked a turbine blade tip. I suspect it was heat and backpressure related. That's the second PS2 I've blown up, so on to a Big Boost 3.4 kit I go.

attachment.png



If someone else wants to try this route, I'd recommend starting out with the Turbosmart TS-0620-3143 wastegate in single port mode with one of the two 7 psi springs removed to take it down to 7 psi. Tune and add spring pressure with different springs as necessary. If you buy an additional 3 psi inner spring, you can mix in match in combinations for 3, 7, 10, 14, and 17 psi initial wastegate spring pressure, good for up to 30 psi or so with those last two with some WGDC added.
 

Bnks334

Sergeant
Dec 1, 2016
396
New York
If someone else wants to try this route, I'd recommend starting out with the Turbosmart TS-0620-3143 wastegate in single port mode with one of the two 7 psi springs removed to take it down to 7 psi. Tune and add spring pressure with different springs as necessary. If you buy an additional 3 psi inner spring, you can mix in match in combinations for 3, 7, 10, 14, and 17 psi initial wastegate spring pressure, good for up to 30 psi or so with those last two with some WGDC added.
Weld the WG shut.
 

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