I was thinking that even guys w/EBC's will see more consistent boost w/the signal coming from B. So, I thought I would try it. On my set-up the WG rpm needed to be dropped a bit, but yup, boost doesn't droop nearly as bad as it did with the signal coming from A (not that it drooped much, about .5 lb. @ 7000 rpm with the EBC setting at 12 lbs). Now it's only .1 lb. I had to drop WG rpm because of boost overshoot :loser:.

So for those guys with an EBC like mine, using Joe's suggestion will also allow for more stable boost control with your EBC.

have to differ on pop off valve location. It needs to be before the throttle body to ensure that the air charge pumped up by the turbo has somewhere to go after the tb slams shut. Otherwise, in very high boost conditions, it'll try to push the throttle body plate down the intake and into the manifold. Probably won't but it may bend it or blow off one of the joints between the intercooler and throttle body.
The explanation for where to put the wastegate sense line is brilliant! kudos!

1. yes.
2. yes.
3. before.
4. yes.

How much of an increase do peiople usually see? I don't really want to jack with a boost controller, but 1 or 2 psi will be a safe increase...3psi means I'll make too much power/torque for my lil trans.

I am using a manual boost controller and can't hold peak psi - it drops like a rock, but not linearly - see attached 13.5psi peak line. I am going to try tapping the cold side piping as you suggest. Would the sharp drop and then slow taper after peak (shown in attached) be indicative of being solved by tapping the cold side, or is something else causing the problem - like too restrictive of a cat causing a weak actuator to blow open or similar?

Attachment 193416

^^ PS - how can one tell if this is the MBC not being able to hold boost or if this is simply a boost spike?

Thank god i read this post today.. Standing ovation from me too.

As for the feed line for the dump valve. Shouldn't that be after the TB?

Nope....you need to have the Pop Off valve installed before the throttle body, since that's where the over pressure builds when the TB slams shut. after the TB it's a partial vacuum after a few revs at least.

If you're using a TB type single point fuel injection and the PO valve is installed after the TB, you're venting potentialy explosive fuel vapors directly into your engine compartment....not a good thing. The dump valve is supposed to loudly go poppoppop, not boom.

Yes, the placement of the valve is before the TB, but the FEED line telling the valve to open..?
I might have misunderstood something very basic here, but isn't the feed line sensing the pressure difference on the other side of the TB, and then telling the valve to open because the TB has been closed..?

Can anyone tell me if my boost drop off in post #65 is the MBC not holding boost or if it's simply a boost spike? How to differentiate between the two? Goal is to hold 14psi. Thx.

Yes, the vacuum/sensing/feed line for the BOV needs to take its signal from the intake manifold.

As stated elsewhere in this thread, you should take your wastegate/MBC signal from the coldside before the throttle body but after the intercooler to help prevent spiking. It is difficult to diagnose a possible additional problem with your MBC until you make that change.

Exactly. I assume the others missed "feed line" in my posts.

As for connecting the feed line, I've used all my connections on the IM. How accurate will the lines be if I start using T-connections, splitting them up?

Will do.

The only reason I asked about spike vs taper before tapping the cold side is because my boost curve seems to be so visually different than a taper (drops like a rock before it tapers, lol). I can live with a little taper, but the quick drop from 13.5 to 10psi is the killer. I just did not want to pull the cold side pipe and tap... if this spike was atypical from simply an intercooler pressure drop.

That works just fine.

Does it matter much if my hose-barb fitting is super small? Will this produce slower spool up?

Finally made this change today and it spikes a little harder initially but then stays dead nuts on target until redline now :)

Hmm... Going to try swapping my source from C to B this week. Might help my part throttle low boost to closed throttle stutter.

You are definitely correct, if your PO valve has a sense line that's where it goes...also note that in partial throttle conditions the PO valve will be partly open, as someone else here noted it's normal for this kind of unit and should not cause any concern. In pure race cars, this type of PO valve is not used (I think,..could be mistaken) and having it increases driveability with a slight decrease in raw performance.

I have the GReddy td04 15g turbo, and it has a connection at the housing for the wastegate. This is ofc in the wrong end, but I still used it at first since I wanted minimum boost when I started mapping.

Today, when I connected my boost controller, I moved the line up to the connection at the 4th runner on the intake manifold.
And my GOD was there a difference..

My car went from getting .25 bar to .4 bar, and that bitch got EVIL.

Massive difference on a GReddy turbo with intercooler. Just massive.