Wastegate Springs

[keith6110]

I bought a 38mm Tial wastegate for my turbo build and my goal for starting boost is 5-7psi.
Now I google searched and am getting mixed results about using the external wastegate and what spring I should be using.

So looking at the Tial spring chart, my goal should be the small red spring ~5psi








I'm using a Hallman pro Manual Boost Controller to manage my boost.

So this is where my confusion is:
Spring says it will open at 5psi, but I'm reading if I were to use a MBC then I can run higher boost with a lower boost spring?




Doesn't make sense to me.

[Galantman03]

Yeah that's right.
Basically, the mbc is allowing you to build more boost by adjusting a spring tension rate and ball. So inside the mbc you can see 15psi, but the waste gate side only sees 5psi. Hopefully that helps

[Galanttuner10]

Exactly what he said, the boost controller basically lowers the pressure the wastegate sees so say you turn the boost controller to 10 psi, the wastegate thinks its seeing 5 still. My spring is the large green 13 psi. External wastegates are the best way to go as long as they vent from the atmosphere to keep the exhaust flow much smoother.

[keith6110]

ahh okay.. So in order for the wastegate to open, it must see 5psi at the "boost line" instead of 5psi in the exhaust manifold.

I was thinking 5psi intake pressure = 5psi exhaust pressure. Which would open the external gate.
This is wrong then ^^^

[Galanttuner10]

My BOV and wastegate use the same port on the intake manifold which was for the EGR valve prior. Everything needs to run off intake pressure

[finald8ta]

im still learning turbos and what not, still reading up,
im working with a 16g with internal wastegate

so what your saying is a MBC wont let the wastegate up at all since the MBC is stopping it from seeing say 10psi and the MBC is now set to 15psi.. and the MBC is inline with the wastegate

im just abit lost here, any help would be great

[Silvertune]

Everything is run off intake manifold pressure. When you go into throttle and build boost it builds manifold pressure. The MBC is put in a line coming off the manifold that sees this pressure and is set to whatever you'd like to run for boost, say 10 PSI. Only once the manifold pressure goes over 10 psi does it go through the boost controller and down to your wastegate. The wastegate has a port BENEATH the diaphragm. The pressure then works against the wastegate spring. If you have a 5 psi spring, it needs 5 psi boost pressure at the wastegate to open it. This is why an MBC allows you raise boost above the wastegate spring pressure; it only lets pressure through once it hits your desired boost and if it's anything above wastegate spring pressure it will open.


The blow off valve is basically the opposite. It has a vac line attached to the intake manifold that runs ABOVE the diaphragm in the valve. This way when you go into boost that pressure pushes down WITH the spring and keeps the valve shut. Then, when you shift and the manifold goes into a huge vacuum spike the vacuum pulls up on the diaphragm and opens so the boost in the intake can effectively "blow off" and either recirculate of vent to atmosphere.



Keith you're best grabbing a 5 psi spring for your gate. Then add boost with the MBC as you move up.

[keith6110]

Thanks a ton for the explanation guys! Very helpful!