I've spent the last hour trying to figure out wastegate and MBC operation.

Here's what I've come up with.

Tial with 1bar spring. In single port, there's a vac line connected from the IC inlet pipe to the side port of the WG, under the diaphragm and spring. When exhaust pressure + boost pressure over comes the spring pressure, the wastegate opens, and boost is limited to whatever boost pressure was needed. By using an MBC, it basically restricts air, so although there is 1 bar of boost, the pressure going to the WG is less than 1bar, thus the WG stays close. Simple enough. Also, i think conventional boost controllers are a relieving type so any extra pressure on the inlet gets vented to atmosphere preventing the valve to open any more than what it's set at. Suppose the controller was a non-relieving valve, pressure would build up, causing the valve to open more than it should, and consequently causing boost to bleed when in single port mode.

In dual port mode, you control boost by applying pressure WITH the spring, basically increasing effective spring rate. Boost control in dual port is essentially the opposite of single port. So if you have the boost controller set such that air flows freely, you'll boost to infinity. Setting the controller completely closed will be just like having a line from the IC pipe straight to WG.

Also, in terms of spool delay between shifts and throttle lift offs, in our cars, the IC inlet pipe never has a negative (vacuum) pressure. So in single port mode, when you lift off the throttle and the BOV opens, the only force closing the WG is the spring. With the stock cycling valve, it used vacuum pressure in throttle lifts to close the WG quickly. So running a WG in single port without the cycling valve will have lots of delay in respool time. Dual port helps to decrease respool time because some of the positive pressure in the IC pipe will be exerted in the same direction as the spring, helping to close the WG.

I think this is right operation for our cars. If I'm wrong on anything, please correct me. However, assuming I'm right, my question is, can't we connect the WG to a line which will get vacuum pressure as well as boost pressure? If you blocked off the IC inlet pipe fitting, then just connected the side port of the Tial to a regular vacuum line, with some sort of variable restrictor in line, couldn't you effectively control boost in a typical single port fashion, plus have a quick respool time since the vacuum created by the boost being vented will close the WG a lot faster?

I'm so confused now.

 

as soon as you let off the boost, the wastegate closes straight away. the idea with the vaccum wont to much the way i see it. the aftermarket wastegates dont open as soon as 1 psi is in the IC pipes, it'll open say around 11 psi on a 14.5 psi spring.

Say your on a track racing... your boosting in 3rd gear then change to 4th. by the time you let go of the accelerator push the clutch change to 4th and press down on the accelerator, the wastegate would of already closed and as soon as your push down on the accelerator the boost is at the quickest spool up untill the wastegate opens.

 

Hmm. Interesting then. I changed my wastegate to a Tial unit, now I'm getting a good second and a half of respool time between shifts.

So now I'm confused about the advantage of running in a dual port configuration. I was under the impression having positive pressure in the same direction as the spring provided some sort of sealing benefit.

 

You running single or dual port?

if you really want to see how it works. Unbolt the pipe of that connects your exhaust to your wastegate and go for a drive and you'll hear the wastegate open and close.

 

Single, using a LBE to up the boost to slightly above spring pressure.

Found an old old MBC when cleaning out the garage today, but it's not a relieving type, so I was getting weird boost activity in dual port mode, didn't trust it enough to do any runs. Going to get a better one and try dual port.

 

i have no exp with the non relieving type but did you make sure the MBC was connected the right way and to the top port and not the side port? and Teed off from the side port line?

Im thinking either way wont the same amount of pressure go throught the MBC either if it restricts it or it realeases it?

 

Yeah, it's all connected the right way. It's originally an old HKS branded unit for an '87 Supra (manufactured by a company called Norgren - http://store.norgren.com/US/en-US/ca...-100-NNAA.html - I think some audi guys and supra guys use it)

My guess for my boost to creep up is that the pressure is building up since it's not vented to atmosphere, causing the valve to open more, more pressure on the top side of the Tial, causing a greater boost, and repeat.

Any idea why in single port my respool time is so long? When I shift and get on the gas again, I get only about 5psi for about a second and a half, then the turbo fully spools.

 

I've got the same brand but it's a relieving type. just checked haha.

I havn't tested single port vs dual port but Read through this thread it may answer some questions. theres a test showing both single vs dual port in a data log

 

Yep, looks like several companies use their products, just rebrand them, if that.

I actually did read through that thread when I was trying to figure it all out... seems like the only thing a dual port does is to allow you to use a weak spring to achieve a relatively high boost. However with a decent size spring, suppose 1 bar, a dual port config isn't needed since at 1 bar of exhaust pressure, the boost pressure will be much much higher since they aren't on a 1:1 config.

 

well if you do go dual port mode you will need to close the boost **** to get the min boost level which is your set spring which will set it back to single port mode because no pressure is travling to the 2nd port of the wastegate.

 

I'm in process of putting car back together now. Got the exhaust on the bench (Fab Speed 3" with tie in) piecing together before bolt up. Using 38mm Tial in dual with a 7# spring. Figure if get stupid during break in might be kinder to me. Just curious if either of you happen to have an 86 951? Seems the head of the Tial wants to occupy same place as the front support of the torque tube.

 

Hey Chris!

I replied to your pm.

Yea, the only gains I have heard about with dual port is guys running an EBC.

Also, the lag in between shifts I was able to tone down with the new diverter valve.

 

Lookl for leaks. You will not have that on a properly functioning Tial in single port with a MBC. Your MBC might also not be reacting well or is not vented. A tial with a MBC will give you a smooth boost curve. I have used this with two different turbos (and electronics) and both spooled up smoothly.

-Dana

 

With a Tial you can run 20psi no problems with the 6 pound spring. The opening of the valve acts against the flow of the exhaust (instead of with the direction the valve opening on the stock one) in a Tial.

The advantage of the Dual port is with an EBC it is easier to run adjustable boost. Also, if something fails in dual port mode, you will be limited to wastegate spring pressure boost (most likely) since you have an unregulated flow to the opening side of the wastegate. This means if you boost controller fails, you get no boost instead instead of maximum boost.

That said, I found the best reaction was to use BOTH an EBC and MBC. What I have done is set the MBC to a few PSI below what I want to use on my MINIMUM boost setting. Then the EBC holds regulates the last two PSI of boost. Then I go to high boost setting and I get another 5psi boost (can go much higher) with the EBC now regulating the last 7psi.

I didnt want to take the wastegate off and put in a new spring (need at least a 10 pound). Tial recommends using a spring that is half the rate of the boost. That is hard to do with two boost levels. Using two boost controllers makes boost spikes go away and seems to improve reaction time of the watsegate.

-Dana

 

Yeah, the top of the Tial is going to be a tight fit with a 1 pc crossover. What I did was thread in like 2 or 3 bolts on both the exhaust and xover side, only like 1 or 2 turns. Then I slowly and uniformly tightened them to get things to line up, and eventually got in all the bolts that way. It's not going to work if you try tightening one side then the other.

You're right, the MBC is not vented, causing boost to creep up in dual port mode since it's opening more and more. Haven't tried single port mode with it, but I would assume the opposite occurs since dual and single port are opposite in terms of MBC operation. Plus it's quite archaic.. probably 20 years. I'll be getting a new one unless I can tinker with it to get it work, but I think I just need a vented unit.

So for future reference - Dual port allows a safety net in the event the boost controller gets stuck in a "full close" position, in which case boost would be regulated by spring pressure. Also, it works better with an EBC. With an MBC, there's not much gain?