Thread: wrong vacuum lines on roller rocker?

Ok so my friend's turbo b15 project is almost complete, the car is put back together but it won't build boost. He is using 3 ply silicone couplers and beaded pipes and as far as we can tell nothing is leaking.

Basically the turbo is spooling fine but the boost gauge stays an 20 vacuum. It doesn't even move at redline. The way the vacuum lines are run is shown below..The black line is the brake booster and the red represents a t fitting. We checked every single line and they're all getting strong vacuum while the car is idling but the car still doesn't make boost.

Because the wastegate actuator needs to see a boost only source. It should not see vacuum. The vacuum is keeping the wastegate from operating.

The boost gauge needs to see a boost/vac source, otherwise it will only show vacuum

Same with the blowoff valve. Needs to see a boost/vac source.

Use a dedicated source for the Wastegate, that's the singly most important device that can blow up your turbo and engine if it's not done right.

A lot of us use the FPR line for Boost gauge, this is not the best way to go about it, but it works well as long as your boost gauge is not leaking air.

Blow off valve should be can be Teed off into the vapor canister/charcoal canister line.

Wastegates are not really designed for vacuum but I have had no issues with having vacuum going to it, it does help the wastegate to close faster after you let go of gas.

Now I will bet that the problem of not boosting is not even in the lines. If there was a massive air leak in the wastegate line, you would be overboosting. It sounds like your wastegate is always open, or you have a massive boost leak in the piping.

Note when I say yours I mean your friends .

To be honest I was not there when the vacuum lines were run, someone else did that aspect of the install and I knew there seemed to be too many T fittings on the brake booster line which is why I figured I would ask.

So being that the boost gauge needs boost/vac source where specifically on the roller rocker motor are you guys tapping in (besides the FPR as Vadim said)


I know this is a noob question (I really am) but where should (besides the FPR line) the wastegate be sliced in? I searched for hours on SR20 forum but only found the diagrams for the JDM motors and nothing about the roller rockers.

I haven't looked at my rr itm in a loooong time, but isn't there a source on the tb that can be used? I think I remember one on the top of it.

Do you know what the name of the line is called? I will look up in the FSM where it is but I just need to know the name and/or specific location.

whenever i run a line to the WG i run it from the hotpipe
drill and tap and put in a threaded nipple

I'm bad with names...


The black hose.

haha even better! thanks bro

You got it bro