Good info and definitely food for thought. The WG bypass entrance and the whole hot side is ported in my FP Green. The merge in the Megan O2 housing is not, although the welds and layout of the merge looked really smooth when I put it on. I'll try the 25# WGA first, and if the reduction in WGDC doesn't help stop the creep, I'll pull the O2 and fire up my port grinder.

 

I've always been hopelessly lost with respect to understanding WGDC's, BCS's, and ECU controlled boost in general. So, I am sailing into unchartered waters here..... but what the hell.

I would feel more comfortable if you would disconnect and plug up the BCS vacuum lines and instead run a piece of vacuum hose directly from the WGA to the compressor discharge tube nipple aka J-Pipe(just for test purposes of course). Try it for me this way just to see if it has any effect on the boost creep issue.

Also, while it is set up this way you can go ahead and increase your WG preload up to 22-23 PSI. Even if this has no impact on the creep it is the right way to set preload.

 

The Megan's have had mixed reviews with respect to boost creep. Some guys claiming no creep issues unported, while others have reported creep which they resolved by porting of the merge hole. Personally, I have found that "golf ball" sized diameter is helpful.

If as you say, your bypass port is massaged, then a flow restriction further downstream at the merge hole in the O2's divider wall may be contributing to your creep issues. At least it seems plausible from my armchair perspective.

Exhaust gases are extremely hot and expanding as they enter the WG exit chamber of the O2 housing. Volume and speed are increased due to the ported turbine housing. It makes sense to me that a too small merge , or crossover hole could be a potential logjam.

 

Hey Sparky - I'll try it when I the 25 psi WGA I just ordered arrives.

Your suggestion is actually what running 0% WGDC does - it connects the boost source directly to the WGA, through the BCS, so that it gets the full pressure signal. To do this I don't need to move any vac lines around. I just set the WGDC to 0% across the RPM range and log boost.

As you increase the WGDC% the BCS bleeds proportionally more and more of that pressure signal to atmosphere reducing the help the WGA gets and increasing the boost. At 100% WGDC, all the boost signal from the turbine outlet is bled to atmosphere so the WGA is getting no assistance. The exhaust gasses are basically blowing the flapper open at that point and only the WGA spring pressure is keeping it closed. In this situation the cross sectional area of the WG outlet is reduced and I'm guessing it is giving me the creeps.

 

Yeah, I think that a too small Megan merge hole in the O2 housing's divider wall is probably contributing to your creep to a significant extent. The Megan is not the best flowing design with respect to the WG. Furthermore, unit to unit consistency has been spotty. Weld quality control has been a problem. Also, more importantly in your case, merge hole diameter is restrictive.

You have to keep in mind that the Megan design with its smallish merge hole has proven restrictive on many stock TDO5HR-16G turbo setups. You have a ported Green, so its lower back pressure turbine is capable of flowing more exhaust gas out through that tiny merge hole than your stock turbine did.

FWIW, I admire the looks of Chad Block's merged O2 dump design.It is somewhat pricey, but I really like that particular design as far as merged dumps are concerned. Check it out on the CBRD website.

 

What, "...boost signal from the turbine housing.....", are you referring to ? How is this supposed signal then bled to the atmosphere? You lost me here!

AFAIK, there is no boost pressure source in the turbine housing. Thus, there can be no boost signal produced therein. I sort of think I know what you mean though. Actually, you were talking about the compressor housing, not the turbine housing, right?

Even in the case of the compressor side, the bypassed boost signal is not vented directly to the atmosphere, is it? Isn't that flow of charge air eventually cycled back into the intake loop via a port located in the intake tube at a post MAF location?

 

You take a decent stab at explaining the working of the BCS system. All of those mini-pulsations tricking the actuator, and so on. This is the theory of the thing. The theory sounds and looks good on paper. Perhaps, under most circumstances it tends to work as you have described.

I am just not convinced that it works best in situations where the user wants to run extremely high levels of preload on the gate. Most guys that use this method of boost control usually run it with relatively low levels of spring pressure. They just assume that the little pulsations are keeping the flapper valve on its seat.

I just think that to really get a turbo to spool as quickly as possible a MBC and relatively highly preloaded actuator spring do a better job than a BCS and moderate levels of spring pressure.

I also feel that an MBC and high levels of actuator spring pressure not only do a superior job of spooling the turbo but that if properly setup can perform as well as a mildy tensioned actuator controlled by a BCS at, and, or near peak boost settings.

 

Fwiw my ported Megan still boost crept
To 20 psi from 6-7 even after porting on a white rabbit with a cut turbine wheel!

 

Were you ever able to control the creep on the clipped rabbit, Ratster?

 

Incidentally, who clipped the turbine wheel for you? Did Forced Performance do it? This was with a fully ported 10.5 housing?

 

Fp clipped it .. Imnot sure because I replaced the housing when I sent it in for an upgrade for a hta 71 with the 11.5 housing that directly according to Robert caused failure of my brand new 71. Likely un ported 10.5 housing on the white rabbit

Robert recognized my specific turbo as one of the early white rabbits with a clipped turbine he had done in the early days

I've got an 18 psi Fp wga that runs 14 I'll be adjusting that per sparkys directions..

 

The FP 25 psi WGA did the trick and my dual fuel set up is now working well. I've got the WGDC% back into a controllable range of 60-80% , rather than the much less managable range of to 90-100%. After tuning EBC I can now hold 23 psi flat on 91 octane and 27.5 tapering to 25 psi on E85. The problem with the FP 18 psi WGA was the spring was a little too weak for the higher boost range I wanted to run for E85.

FYI - It looks like FP have stopped making the 25psi WGA and I was lucky to pick one up from a fellow evom member.

 

I am glad that the 25# gate cured your creep issue. This is the first I have heard that FP will no longer be offering the 25# actuator. I have a brand new one sitting in a drawer somewhere here at home too.

 

I'll send you a 9.8 housing for that actuator

 

Let me think on it as I already have a deal in the works with a friend involving that actuator. If that deal doesn't finalize, I will surely let you know. Thanks for your interest.