after my white/ported mani/hotside/epm dump instal my forge mbc isnt do what i want. i was running 21 pounds pretty steadily before but i know have the mbc bottomed out on the low side and am still seeing 24-25 psi in 2-4 gear. its not spiking or creeping up there either its holding steady. any thoughts? might just ditch the forge and get a boost valve but i wanted to see what you guys thought. i also might try rerunning the lines. the bov is teed off the line form the manifold to the mbc right now i thought that might be affecting it. any input will be good.

 

Try re-routing the lines and giving each nipple it's own dedicated source.

 

So, MBC is sourced off the factory line that connects the IM to the DV, right? So, this boost reference line is routed to the bottom port on your MBC, right?

 

yes. and i never had a prob before with my 8 turbo and nothing was changed besides the said parts. it just seems that the lowest setting is too high at the moment. not a huge deal as ill be getting tuned soon on much more boost but im just curious.

 

As a practical matter 24-25# of boost should not be a problem on E-85 with your setup. So, I don't know what you are worried about.

The White is a very fast spooling turbo. At least as fast spooling as the stock turbo it replaces. It is configured with a very low inertia, and low mass rotating assembly. Its highly efficient HTA compressor wheel flows 10% more air than the stock comp wheel does.

The recent mods which you mention all have the end result of reducing exhaust back pressure on that fast spooling, low mass, low inertia, high flowing turbo. You are bound to have boost creep issues.

Due to the reduced backpressure and the low rotating mass it is harder for the unported, wastegate bypass port to bleed off sufficiently the increased volume of exhaust gases flowing through the turbine inlet area.

You would need to port the bypass port in the turbine housing so that the WG can keep up with the increased exhaust gas flow due to your new mods. When FP ports the turbine housing, they port the turbine inlet area and the turbine outlet areas of the turbine housing which further reduces back pressure. But, they do not address the WG bypass port whatsoever AFAIK.

EDIT: When the EPM O2 Dump was first released, Robert Fuller commented to the effect that the WG dump diameter was a bit small and restrictive. That particular design focuses on maximizing DP diameter and flow at the expense of a slightly reduced WG flow. So, the EPM design should reduce backpressure, but at the same time it may tend to restrict WG flow(I'll zip-up and adjust my flak jacket).

 

im not worried about it but im not on e85 right now im on pump 93. i still need my tune for e85. either way you still did not answer my question. i should still be able to control boost none the less, moe than i am able to now. i was expecting to have to make adjustments on the first drive but not being able to go down below 24-25 psi doesnt make much sense to me. im well aware of the specs of the turbo. and the turbine outlet was mildly ported as well as a little of the scrolls passages. sounds to me like your diagnosing creep more than just seeing a set psi. either way thanks for your responses ill re run my lines tomorrow and see what happens.

 

How would you do this on an ebc without tapping into the bov line?

 

this happened with my buddies red on a different mbc... He had to put either a stiffer or softer spring in, sorry im not sure which.... But 24-25 is fine, are u self tuning ur car?

 

It's not tapped into the BOV line from the factory, so nothing should change. The bov has it's own source from the hardline bolted along the valve cover area, here's a pic. The part with the blue hose:




If you don't use/have that hardline, it looks like this (big ugly silver hose)



or this.



The line off the turbo goes to one port on the MBC, and the other port is to the wastegate. So you're just sticking something inbetween that line to restrict the flow.

Here's another ugly pic for you. This long vaccum line is ran from the turbo straight to the wastegate, no boost controller. With an EBC it works the same way, stick the solenoid right in the middle, turbo to one side, wastegate to the other.









But to the OP, Sounds like Sparky is right on the money about what your problem is.

 

Keep the boost low till you get it worked out, dont want to have any problems like a blown motor.

 

lol this it what im trying to accomplish just til my tune but this is as low as she gettin.

 

I t'ed into the bov line, where else can I tap into manifold vacuum?

 

Those "unwanted" 3-5#'s of additional boost which you are seeing are mostly the result of the 3-5#'s of total system backpressure which your new mods eliminated. However, your marginallly adequate WG system is not able to bleed-off, or bypass those newly released pounds of boost which you have freed up by reducing backpressure to an equal extent.