turboted

I know this topic has been discussed many times...but I can't seem to find the answer I'm looking for. When using a dual port wastegate, is it better to contol boost with a black **** MBC or an accuboost MBC?

http://www.boostsciences.com/accuboost.html

http://www.boostsciences.com/mbc.html

I have a Tial 38mm dual port wastegate and have been contolling it with an Accuboost MBC. I have had 0 problems. But now I'm wondering if I should switch to the black ****. Is there a significant difference in managing boost either way? TIA.

nize

i don't think you can run correct dualport mode with the accuboost, because you can't vent to atmosphere. running a proper dualport setup requires the ability for the boost controller to vent to atmosphere.

i haven't read the specs on the black ****, but i'm guessing it should vent to atmosphere.

turboted

I think I am missing something here...how/why would a boost controller vent anything to anywhere? It's my understanding that the wastegate vents the boost pressure (either to atmosphere or back to the exhaust, depending on exhaust configuration). The MBC simply controls how much boost pressure gets sent to the wastegate to vent. Right???

It is also my understanding that the 2nd port on a dual-port wastegate is designed to hold reverse pressure against the valve until the pressure threshold is reached and the valve opens. In doing so, it prevents the wastegate valve from leaking any pressure before threshold is reached, at which time the valve opens completely and all at once. From what I can tell...the Accuboost MBC does not bleed any pressure to the wastegate until the pressure threshold is reached - like and on/off switch. In contrast, it appears that the black **** DOES bleed a little pressure to the wastegate before the pressure threshold is reached for the purpose of providing back pressure against the wastegate valve (through the 2nd port) so it doesn't open partially or prematurely.

Am I way off here? My understanding is based in theory...not so much actual experience. Case in point, I have never taken my Tial 38mm apart to see how it works. But it seems to me (based on above) that contolling a dual port wastegate with an Accuboost MBC simply results in operating the wastgate in single-port mode, thus dimishing the point of having a dual port wastegate to begin with.

sawood12

Turboted, you are bang on in your description of the workings of a DPW. The DPW is a comparitor - it compares the manifold pressure to another pressure signal that is regulated by a device whether it be an MBC or an EBC. I'm not sure how an Accuboost works but I can speak from experience with regards the MBC. The MBC allows the pressure signal to rise with the manifold pressure upto a maximum pressure that you set with the black **** with the help of a boost gauge. Because the pressure on both sides of the DPW diaphram is the same the wastegate valve is positively held closed until the pressure hits the set pressure. At this point the manifold pressure will open the wastegate therefore regulating the boost pressure at your intended boost pressure.

There is nothing wrong with an MBC. It might not be as good as an EBC but it works fine and is a robust and reliable valve in my experience.

If an Accuboost works in the way you describe then you would get all sorts of problems if you tried to use it with an DPW. If you connected it to the 2nd port as you would an MBC then it would not see a pressure signal at all until you hit your intended max pressure so until then the exhaust manifold pressure would just force the wastegate valve open and you'd either have massive turbo lag or you would not achieve significant boost pressure at all. By the way i'm referring to a Lindsay DPW where the arrangement means the exhaust manifold pressure is trying to open the wastegate valve.

Trucho-951

turboted, i've tried both accuboost and black **** MBCs with my 0.8 bar spring 38mm Tial, and have even tried them simulatneously. I get about 200 rpm faster spool up with the accuboost type contorller. The boost curve has a sharper transition from rising boost to steady boost. The black **** mbc boost curve shows a somewhat more rounded transition. So IMHO the accuboost is the better of the two MBCs.

However, from a safety point of view the Black **** is a better choice, because if it were to clog and fail, it would fail in a "fail safe" mode. Maximum boost would be 12 psig.

The accuboost on the otherhand, if it were to clog and fail, it would block off all signal to the WG and the engine would overboost, max boost would be > 25 psig??? as it would be similar to running with the boost signal line clamped off.

I think you are fine with the accuboost, if you go with the black **** you will not feel any improvement.

turboted

Exactly what I wanted to know...thanks Trucho-951.

nodestination1

Not true at all. Say you want boost to be set at about 15psi... for the sake of the example, let's say 1 bar. keep in mind that the tial 38 comes with a .8 bar spring... Im guessing lindsey is roughly the same. Thus, once the manifold pressure reaches .8 bar, the wastegate valve will open. If you hook up an accuboost to the top port of the wasteage, the accuboost will be exerting roughly .2bar of pressure, to increase the initial .8bar of the spring to 1 bar even. It is true that the accuboost is an on off switch, so it will hold off all pressure until you reach .2 bar of boost... much less than the required .8 bar to open the spring.

The only time the accuboost would be inefficient is when the pressure exerted to the top of the wastegate is above .8 bar... so you'd be running about 1.6bar of boost, much more than most rennlisters.

I could be totally wrong here, but thats my understanding of a dp wastegate.

sawood12

You're right, you would have to connect the accuboost to the top port of the DPW, and not the 2nd port as you do an MBC. But even then what would you connect your 2nd port to? Not your manifold pressure as it is unregulated and would not open the wastegate at all and certainly not to atmosphere because all you'd have is a very expensive Lindsay Boost Enhancer. In fact you'd need to connect an MBC or EBC to the second port and in that case what is the point of connecting an accuboost at all?

I know the Tail DPW's have a spring but i'm not sure about the Lindsay ones. In theory why would you want a spring on a DPW at all? It just means that if you want to achieve 1 bar of boost you need to set your EBC to 1 bar plus your spring force. That is just daft. You just want to dial into your EBC the boost pressure you want to achive and let the EBC do the work for you.