Braineack

iTrader: (62)

yeah i'd try block off the bleeder hole, that might actually be the issue.

AbeFM

iTrader: (3)

Hey, that works really nicely. What's the lowest boost you can run? Mechanically, my system isn't up to it, I can't boost lower than 10 or 12 anyway. But, I think I'll try it. Soon. I could run a couple more lbs of boost if it wasn't for hitting overboost cut off all the time.

I'm obviously missing something here. Maybe you have the spring drawn on the other side?

force diagram time:


Ok, the plunger has 3 forces on it, the front and back of the valve, and the total force from the diaphragm.

The wastegate has a pressure differential across it, or nothing would flow. Or, think about this, the manifold has high pressure (which spins the turbo) and your exhaust is pretty open, probably 3" to minimize back pressure. I doubt it's really 10 PSI, but I didn't want to say 0 and have people say I'm stacking the deck.

So, the 1" valve (probably smaller.. 20 mm?) has 30 psi on front (compressor outlet pressure x2 - let's say it's a modern turbo. Old turbos had 4 or 5 to one pressure ratios). That's 20 net pounds of force pushing it open. So we need at least 20 psi on the diaphragm to keep it shut.

The "compressor reference port" I'm assuming is literally looking at the output of the compressor. In general, this will be peak MAP plus losses across throttle body and through the intercooler. Probably 3-5 psi at full tilt, but then a bit higher (that's why you have a BOV after all). So, saying you run 15 psi, 20 is pretty reasonable, test you BOV if you're curious.

Now, your boost controller basically shuts off pressure (you're trying to control boost, right?). Certainly an MBC will shut off pressure, that's all they can do, shut it off or let it through.

Lastly, the spring puts a force proportional only to displacement (the more the plunger opens, the more it pushes. I said 10 lbs but now I'm saying 50 lbs. It could very well be something quite different, but it's fixed at any given point in space.

2 psi * diaphragm area (call it 3 sq in?) = 6 lbs
20 psi * diaphragm area (same on both sides) = 60 lbs

So now you have, total:

Closing forces:
Spring: 50
Boost Controller: 5
Dump tube Backpressure: 10
TOTAL: 65

Opening forces:
Compressor Reference: 60
Ex Mani Pressure: 30
TOTAL: 90

So, here you have 25 lbs trying to OPEN the port while you're telling me you're at at part throttle. Opening the port will lower boost. Which does exactly what your guy said it would. Heh. Makes sense to go through it all slowly like.

Just for fun, let's look at building boost:
Compressor Ref = 5 psi
Boost Controller = 0 (boost controller) OR 4.5 psi (assuming no boost controller, just manifold ref signal. 4.5 psi becauses losses are minimal at low flow)
Exhaust pressure: 15 psi
Dump Tube: 2 psi


Spring is closed now, less displacement, less force

So now you have, total:

Closing forces:
Spring: 40
Boost Controller: 13.5/0
Dump tube Backpressure: 2
TOTAL: 55.5/42

Opening forces:
Compressor Reference: 15
Ex Mani Pressure: 15
TOTAL: 30

This is what I was worried about, basically, you're asking the spring to overcome the difference in pressure lost in the IC and the TB. With a boost controller, it only gets worse, in fact, it's so close to not doing the job you have to question the assumptions/numbers I put in.

Basically, it should be fine as long as your spring pressure is close to your running pressure, and your intake track is smooth.

Things its sensitive to:
Spring pressure - you're asking it to do most of the work here, so make sure it's right
Ratio of diaphram size to valve size - this is pretty fixed
Inefficient turbo/low back pressure on dump tube


Anyway, what do I get out of all this? It IS bad for building boost to have the compressor reference in there, but it will help give you tighter control when you need it. If you can't make boost, lower the losses in your intercooler and throttle body, or get a bigger spring.

You know, looking at this, what it seems like you really want is the boost contoller port to see manifold pressure, and the compressor reference port to have the MBC in it. Then, building boost:

So now you have, total:

Closing forces:
Spring: 40
Boost Controller port: 30 (10 psi in mani)
Dump tube Backpressure: 10
TOTAL: 80

Opening forces:
Compressor Reference: 0
Ex Mani Pressure: 30
TOTAL: 30

That makes it seal VERY well. And, limiting boost while wired up this way:

So now you have, total:

Closing forces:
Spring: 50
Boost Controller Port: 45 (15 psi in mani)
Dump tube Backpressure: 10
TOTAL: 105

Opening forces:
Compressor Reference: 60 (20 psi at compressor)
Ex Mani Pressure: 30
TOTAL: 90

Very close to opening. With smarter numbers (better spring) it would totally work. This would work well in both situations

So, I'd say, your MBC should go between the compressor outlet and the compressor reference port, and your boost controller port should go to the mani. The only problem here is you're going to get the same issue with falling boost at high flow (rpm&tps) that I was.

Jesus, I feel beat down. :-) Guess I'll post it and let people pick it apart.

Zaphod

Lowest boost I can run? Don't know - wastegate I suppose ~5-6PSI. Now I am aiming at 10-11 PSI. (165 kPa)

AbeFM

iTrader: (3)

Ah. My wastegate (internal) isn't up to the job. Which means wastegate control is harder because even with the flapper mechanically unhooked I still get quite a bit of boost.

Faeflora

iTrader: (2)

It's not difficult- you unbolt the lid, the spring flies out violently, you crush the new spring in there, and bolt the lid back down. You will need to order a new spring from Tial.

BTW in my limited experience, when running Tial wastegate, the turbo will spool more rapidly with a stiffer spring. I went from a 15psi spring which hit 15psi @ 3500RPM to a 9psi spring which hit 9psi by 3900RPM. I added in a FM solenoid for Hydra EBC and "tuned" the EBC for 12psi but couldn't hit 12psi earlier than 4100RPM. This was in the same day, like 1 hour apart.

I'm guessing this happens since the WG doesn't open all of a sudden when you hit the spring rating. It opens gradually as the spring compresses while you're in "lighter" boost. I recommend running as heavy a spring as your motor can handle so you can spool more efficiently.

hustler

iTrader: (6)

Well, my motor can handle 20psi from my turbo with no problem, I don't really want to tell the oracle of a 20psi track day though. I'm happy at 11 right now, but may throw an 18psi in there for the street.

AbeFM

iTrader: (3)

That's just what I was saying - you're relying on the spring because you're forcing the wastegate open with compressor pressure. Ideally, you'd want a solenoid to close off that line and open it only when you're at your boost target.

One thing I've always heard, you want a wastegate that's mechanical for JUST below your boost target, and use the EBC to do the fine control. Of course, it would SEEM that without the pressure on the back side you'd be better off with a bigger gap. All I know is people who had issues and fixed them swear by getting a matching spring.

Very true. F=-kx -> The force on the flapper and the pressure in the wastegate go up till it opens. So it'll get pushed a little bit open the whole way up. This is another reason for a good EBC, it'll keep the pressure off the valve till you're ready to open, giving you a faster spool

naarleven

iTrader: (2)

Greddy Profec B Spec II Boost Controller MYR 400

hustler

iTrader: (6)

I was all hot until I read this: "

Seller's Country: Malaysia"

chriscar

iTrader: (24)

I'd stay away from that controller. Too confusing to setup. And once you do get it setup (evolutionm.net has a great writeup), you'll forget how to do it a week later, so on-the-fly changes are ftl.

The Profec B was great. Greddy fucked up by over complicating the SpecII, and then redeemed themselves with the S, which afaik is just a B with chrome *****, and the nice small SpecII solenoid.

C

naarleven

iTrader: (2)

Literally just saw that myself.

I'd like to get a manual controller like that. I was looking at a AEM Tru Boost for a while, though its vastly more expensive.

AEM - TRU-BOOST Gauge-Type Controller

Faeflora

iTrader: (2)

So you mean hook up your EBC and MBC like this? Where the MBC bleeds off psi from the compressor?

hustler

iTrader: (6)

I had a profec B in my VW....I don't really need it with this wastegate though. I'm going to just but an 18psi spring for the street, 11psi for the track.

Laur3ns

What do you dyno at 11 and 18psi? Why not grow ***** and run 18 all day long. All you have to modulate is your corner exit and fix your brakes

AbeFM

iTrader: (3)

Ha. I have to think about it. :-) I'll try tomorrow.

As to the 18 psi/11 psi thing, gear dependant boost target, TPS dependant boost target, or just worse spool, all of those would help you hold corners.

AbeFM

iTrader: (3)

Ah, when I said it, I meant without the EBC. From the way it's been described, pressure can only make the wastegate hold shut. Unless the EBC is set up to work backwards... Meh.

hustler

iTrader: (6)

My boost controller died, but even with a leak at the turbo/dp I was making 240wtq at 10psi on a mustang doing load pulls (turbo would not make more due to the leak). I've had it overboost to 230kpa and its exciting. The car feels just as fast at 11psi as it did at 15psi last time...judging from the way it rolls c5's on the highway.

For everyone who's telling me to put the MBC on the bottom port only, I did and its abject failure. Apparently the bottom chamber holds enough air that the MBC won't dump the air quickly enough to function properly, and it also overboosts to "230kpa protection." I guess its just time to buy a real boost controller since I've had to buy "real everything else".

gospeed81

iTrader: (51)

Once again...another thread where hustler is missing the simple solution.

You have a badass WG...just change the springs. Simple, easy and effective.

I can see it being a bitch when the motor is hot....but really, when you wake up in the morning and assess how much like a man you feel, you pretty much know what kind of boost you want to run....and it's only slightly more work than fiddling with a MBC.

hustler

iTrader: (6)

stfu, motherfuck. turning a **** > 6 bolts, 2 springs, lots of pressure, stfu. Its a bitch.

gospeed81

iTrader: (51)

No...you're just a wimp.

Man up and do it right. You act like you're going to rice around hittin' switches to change boost targets for every pass. Make life easy on yourself.

In all seriousness I just took my MBC off. It worked well enough...but I could lengthen the rod easier and more consistently for my boost target.