oldman does free popoff, to go along with free wastegate

[Oldman]

OK, so for grins, I made a free pop-off valve.
Specifications:
Hobbs switch left at 17.5 cut in, factory TB used with the EGR pipe removed thus dumping the bypass intake gasses out of the factory TB to EGR hole. I used all factory vacuum lines (as this is their original route) and used the factory EGR solenoid valve for control. This appears to be a negative triggered device (FYI). VNT settings at zero, 11mm pump, chip, .205s

Surge in the intake can be controled via the EGR valve venting intake charge to atmosphere. This is a good thing because the VNT-15 maps (as all turbo maps) have surge lines that are MUCH higher at higher flow levels. To put it simply if you going to blow the turbo it will be at high boost and low flow situations, NOT at high boost and high flow situations. So poping some flow is a good thing for wheel longevity. An additional plus(es) are that venting intake charge presents no plumbing or soot problems, is quieter, and it takes almost ZERO time to create such a device.

Results were less than spectacular. Tip in surge can go to 25 PSI and then oscillate at WOT between 15 PSI to 20 PSI. I speculate that the factory valve has a hard time opening against manifold pressure without massive help from the now unplugged EGR. Still this shows that a Pop off is effective and I'd prefer this to any negative VNT mods. I would also think a real pop-off valve should be used. They are CHEAP!!!!!

With popoff in operation, the car seems more powerful and reaches boost much quicker, hmm, don't know why.

On the free EGR wastegate, here is where the testing has reach to my mind a conclusion:
I tried to plumb the wastegate into the VNT control line, we know that this is NOT an ON/OFF binary setup. The factory modulates flow to control the vanes. Well I can get no boost, with even a whisp of vacuum in the line the EGR port opens and there is no turbo spool. I was VERY surprised as I expected some boost even with the port full open. This shows that the EGR hole is MORE than sufficient to bleed boost away. So there is no cheap control for the EGR wastegate cheap = free, Hobbs switch for under $30.00 is the only control method, but I got an angle.

I did also hook the EGR wastegate and the pop off device to Hobbs control. This would be bleeding intake as well as exhaust. To my surprise surge was higher with this setup, as well as the oscillation in boost say between 15 PSI and 22 PSI. Not good. I'm speculating that the factory vacuum supply just is not enough to pull open both valves in a timely manner.

[ March 22, 2002, 19:52: Message edited by: Oldman ]

 

[Davin]

Originally posted by Oldman:

With popoff in operation, the car seems more powerful and reaches boost much quicker, hmm, don't know why.

<font size="2" face="Verdana, Helvetica, sans-serif">How's this? When the popoff does it's thing, the MAF sees plenty of airflow, so the smoke map doesn't choke off the fuel supply. You're pounding the throttle, mixture is richer than normal, hotter EGTs and faster spool rates. Whattaya think?

I think this is a good idea, and you are 100% right that low-flow conditions are what's stressing those failed high altitude turbos, not the high-flow situations.

-davin

 

[MacGuy]

Oldman, any chance for some pictures and how - to. It will make many of us happy to get rid of those 25 psi boost spikes (surges) and save turbos. Thanks!

Golf Y2K, 5 speed
UPsolute; 0.205's; PiperX panel

 

[Oldman]

Nothing really to see here, stock TB (from my spare 110 HP motor) is bolted to the lower EGR tube which has been unbolted and rotated 180 degrees. I use the stock vacuum line and the stock EGR valve. I've run all my on electric controls but I'm going to change that to a single negative control wire for the entire setup.

The stock EGR control appears to a negative ground control setup, so I want to leave the stock yellow wire in place (the hot wire which is one of two EGR control solinoid wires) and ground the red wire (which appears to be the ground trigger wire) via the Hobbs switch. So the spec would be cut the stock red egr control wire, run wire to Hobbs switch, gound other side of Hobbs switch. Simple?

I know of several EGRs from carbed turbo engines (hint) that would work wonders as an external wastegate, for guys that don't have an extra TB sitting around.

Pop valve is the same deal. I move nothing from stock. The EGR tube has already been disconnected to make a wastegate so. To fool with the pop off I needed about 3 inches of vacuum lines and a vacuum T. Like $2.00 worth of parts.

One good thing about the popoff is that it does not require an extra TB!!!

Really I'd work further on this, but I'm in an advance degree program now and the wife is going back to school. So the best thing for me to do is weld the hood shut for a year.

[ March 23, 2002, 16:20: Message edited by: Oldman ]

 

[Oldman]

From two weeks ago on VWVortec
I've have setup a Hobbs switch at 17.5 PSI through a relay to open my EGR valve in order to control boost. I致e installed a green diode to tell me when the EGR is working. My intensions are multi-fold:
1) save the shaft by not running the wheel into the surge lines
2) save the engine by not over boosting it.
3) keep the VNT setting near stock or at stock for drivability and low smoke
My reasoning for circulation EGR gasses back into the intake is as follows:
1) The dead (low O2) exhaust will dampen flame front. Reducing the heat and velocity of the expelled exhaust
2) The recirculated EGR gasses displaces some of the intake charge at the same time reduces the amount of exhaust gasses passing through the turbine; helping to reduce turbine speed and the resultant surge in PSI.
3) I知 am using the stock EGR cooler, and still passing all gases out thought the CAT, thus keeping pollution to a minimum.
Results are as follows:
1) Surge is not lower, It used to peak out at 21.5 PSI now it goes to 22.5+ PSI peak.
2) sustained boost is also higher. Used to be at 17.5 PSI now it is at 19.5+ PSI.
Conclusions are as follows:
1) PSI in the manifold results from a backlog of intake gasses, that said, introduction of EGR gasses increase peak pressure at surge and through out the RPM range, the opposite of what was intended.
2) The EGR introduction at high boost levels does nothing to alleviate turbine speed and subsequent momentary compressor surge.
3) The exhaust is under a far higher pressure vs the intake and the flow from the EGR is significant.
Follow up speculations:
1) a true Wastegate on the stock EGR hole will not work in dampening boost overshot, the VNT spins the turbine up too quickly and even dumping large amounts of exhaust out of the Wastegate at 18 to 20 PSI will not stop the VNT over shoot situation.
2) A popoff valve maybe the only way to control intake manifold surge with a VNT turbo.
Popoff valve implementation would be as follows:
Popoff would have to be controlled by Hobbs switch as a standard Popoff works with a pressure line before the throttle and a vacuum line after the throttle. When the vacuum line reads lower than the throttle line, the valve bleeds away boost. This is done to save the compressor wheel from surge and to help keep the wheel spooled.
On a TDI, a popoff would, keep the compressor wheel from overshooting the boost islands and going into surge. As well as limiting total boost seen in the intake and engine. This is a high compression TDI; hopefully keeping max BAR within reason.
A popoff is much easier than a wastegate to plumb and it is cleaner to dump air than exhaust.
Errata
Before installing my new pop off, on a custom bent intake tube made out of polished stainless. I have done the following.
Created a true wastegate using the factor lower EGR to cooler pipe and the factory throttle body (AKA anti-shudder body) with the build in EGR.
I unbolted said tube and rotated it 180 degrees, bolted the TB on to tube. I connected vacuum line up to stock EGR vacuum control. Hobbs switch set to 20 PSI.
Results are as follows:
Car can hit 20 PSI under low speed high gear conditions. Such as 1300 RPM in 5th. Historically this has shown to be the highest surge situation. The EGR pops open at 20 PSI and drops down to 17.5 PSI where the Hobbs switch closes the valve. It will osilate in the 17.5 to 20 PSI range as long as WOT is maintained.
The motor seems to hit boost much quicker, without fiddeling with the VNT, I would speculate this is caused by the reduction of backpressure through the EGR. I thought maybe this was a placebo effect, but after a full day of driving the car is noticeable stronger a WOT and power response derived from initial WOT tip-in.
Smoke, seems unaffected. I壇 like to experiment more with positive VNT settings to find a no smoke solution. Using maximal intake flow combined with EGR dumping.
Noise, the EGR wastegate is quite and only a slight wosshh can be heard while in operation.
Conclusions:
Cheap wastegates can be made from stock parts and stock controls. Due to the high PSI backpressure in the VNT manifold the small ported EGR is surprisingly effective. Surge is completely and totally gone.
Followups to be tested:
1) Positive VNT settings -1, 0, +1, +2.
Anyway, I went to lunch today since Freds place is down. Of course that meant I went home and fiddled with my TDI. I've set the Hobbs to open at 17 PSI and I've put the VNT to stock = 0.
Boost surge can go to as high as 22.5 PSI, but most of the time it stays at or under 20 PIS, boost will fluctuate in the 17.5 to 20 PSI range through WOT.
I'm sure with fooling around I can get maybe a 19 to 21 PSI fluctuation, with a -1/2 to -1 VNT. Max surge say to 21 PIS.
How痴 the power? Tire spin with as little as ｽ throttle in 2nd gear, hows that? Overall power is up over -1 VNT setting and over the -2 VNT settings. Initial power and throttle response is un FRIGGEN real. With wheelspin found in 2nd gear and ｽ throttle on three separate occasions just driving back to work! SOTP dyno says power is higher than it was at -1 VNT by 5+ HP, making this about 160+ HP to the wheels.
Smoke from normal driving to ｽ throttle is also completely gone. WOT smoke? Don稚 know as I知 trying to keep the car with all the new power on the road instead of the ditch.
Let me say this and I知 hope I知 not tooting my horn too much. My TDI is the ultimate TDI, buku power, instant throttle response, and it has NOT flown apart.
This is the finishing touches to my magna opus. I have one of the most powerful and most drivable TDIs on the planet. Who can want more?
Final configuration as far as I知 concerned:
11 mm pump
.205 A3 non shimmed injectors
Upsolute
Oldman intake
stock 1.8T paper filter
All screens and tubes in place and clean
Amsoil 3000 oil
DGeek short shifter
DGeek oil cooler
EGR Wastegate
DGeek light steel flywheel and upgraded clutch.
Caracture roof spoiler
TT Take off rims
Intercooler spayers (two sides)
Future mods (not one for more HP):
Rear sway bar DGeek
Bilsteins
Stock WE/GTI springs if they are cheap or free
17x7 rims and Michelin Pilots 225x40s
Lexus Pearl white metallic paint
Aftermarket leather seats two tone
LSD

 

[**DONOTDELETE**]

&#30693 &#30196 &#65405 &#65405 &#31258 &#30693 &#30693 &#30693 &#30693

I didn't know you knew Japanese.

 

[Oldman]

ea wackani masen, desho? With a wife named Kazuko and a child named Musashi, I figure my speaking will catch up?

 

[Boundless]

In case any body doubts oldman's recommendation for the bleed technique to get more flow through the compressor to evade stall (surge), it is proven standard operating procedure in jet engine compressor sections. On a jet engine, the bleed air is taken uniformly aroung the entire circumference of the compressor sections. Real nice for balance, uniform flow and pressure fields.

Concatentated multi-stage compressor sections in centrifugal compressor turboshaft and axial flow engines use this bleed technique for the purpose of ensuring stability (evading surge) of each compressor stage. If one stage stalls, they all go down and an engine stall is a scary thing.

oldman does use the word "surge" for "boost spike" also, but his mod will also take care of surge instability that may occur on the way to achieving the boost spike.

Great mod oldman!!!

 

[Rapt]

Two questions here...

First, did you do something to avoid getting the CEL because the EGR is no longer EGR'ing? (or was that done at some point in the past?)

Second, you named your son MUSASHI???.... Wow thats a lot to live up to.

 

[Oldman]

Yeah and the daughter is Yamato! Packing 18 inchers.

Up I use the FART method on the EGR, I have never touched my MAF lines, I don't even look at them hard.

 

[rrick]

hey project time, i guess. Lookin at the boost gauge after upsolute and vnt tweekin (not for performance, new turbo wansn't factory adjusted) makes me think a mod like this would be nice (and cheep too!). Thanks for the idea oldman.

So, to minimize boost spikes that show up in the intake, bleed the intake boost?
So, to minimize turbo shaft overspin (altitude damage?), bleed exhaust pressure?
Or hey, bleeding only one side would take care of both?

grrr, whats your take on "TB" (tuning box, timing belt, turbo, thomas j. benson)

 

[Oldman]

.I've only done one follow up. I've tested the stock EGR solenoid and found that indeed it is a negative triggered device (a good thing)

So to make a pop off vavle:
Take tube off from bottom of TB
Install block off plate on the exhaust manifold to EGR tube (simle piece of metal with two holes drilled in it for the two exhaust manifold studs)
Cut red wire from the EGR solenoid splice it to a wire leading to the Hobbs switch.
Ground other terminal of the Hobbs switch
Install Hobbs switch into intake track somewhere after the turbo.
Adjust the Hobbs switch to where you want max boost.
You need not remove a single vacuum line.

If you need to build a wastegate.

Install any wastegate or EGR gate to exhaust manifold (I just used an old TB and the stock EGR tube rotated 180 degrees)
Install vacuum line from wastegate to EGR solenoid.
Wire EGR solenoid for ground trigger spec'd above

Questions?

 

[AtomicSushi]

Has anyone else tried this. Thinking very hard about looking into this, as I have plans for more boost in the future.

 

[Oldman]

I'll install the dawns device and or use the N75 switch from an A3 to slam the vanes open, if this works and we already know the dawns device works, then no pop-off or wastegate is needed, at leat upto 156 WHP.