Big Can Wastegate...

[mcglsr2]

...got one on my 0.48 A/R Garrett. It's the non-adjustable one. Does anyone shim them or is there an issue with boost spikes? Any need to shim it, or can the big can variants handle more pressure before cracking open? Does anyone know at what relative boost pressure these things start opening?

I understand it depends on the backpressure in the exhaust, but educated guesses are appreciated. For specifics, I've got a ported exhaust manifold, 3" TU sv and 3" exhaust. So I've minimized back pressure as much as I can considering the 0.48 bottleneck.

[shadow88]

I found about 11 unmodified. No bleed, no restricors, nothing.

[GLHNSLHT2]

boost should be 5-7psi with a straightline to it.

[mcglsr2]

I found about 11 unmodified. No bleed, no restricors, nothing.

boost should be 5-7psi with a straightline to it.

Alright, so if I run a hose straight from the manifold or compressor, it will hold 5 to 11 psi, depending.

Okay. What if I use a MBC? And I set the MBC for say, 18 psi. Which means the wastegate isn't seeing anything on the hose. All it's seeing is pressure against the puck from exhaust pressure. Will the big can keep the puck closed until the I hit 18psi, at which point the MBC cracks and shunts boost to the wastegate, thus opening it? Or will the wastegate start to crack open from the exhaust pressure long before I hit 18psi? And if it does, about where does it crack open? I'm guessing that answer is between 5 to 11 psi? Can that be right?

[GLHNSLHT2]

that's right.

[mcglsr2]

that's right.

Hmm, well then I'm not sure I understand. How in the world do we get to 20psi then? If the stupid wastegate starts opening at 5 to 11psi? It would be even worse on the smaller wastegate.

And if what is indeed the case (the 5 to 11 psi boost pressure which relates to x amount of exhaust pressure which is pushing the puck open), what do people do to counteract this? Are people shimming the can? Or using an adjustable actuator arm and setting some preload, thus tightening the spring?

[GLHNSLHT2]

Sorry guess I should of clarified. Unless you have huge amounts of back pressure. the puck won't open until the desired boost level set by the MBC.

[mcglsr2]

Sorry guess I should of clarified. Unless you have huge amounts of back pressure. the puck won't open until the desired boost level set by the MBC.

Oh, okay - and I apologize, I wasn't really asking the question the right way That makes sense - explains why if you unhook the boost hose to the wastegate you spool your turbo into oblivion.

So what this means is that it's not really worth shimming or preloading the big can wastegate. Maybe on the smaller one, but not on the big one. And all I'm doing by shimming it is encouraging boost spiking. Correct?

[Vigo]

You got it. The big can is strong enough that it can hold the wastegate puck closed way past 20 psi and the reference air line has nothing to do with it.


So basically there is no reason to shim or modify it at all other than for fitment reasons, but you shouldnt need to do that either if you have a stock bracket/compressor housing.

[shelbymonster]

i have the small can on the charger , the arm is preloaded , without vacc im having 30+psi , so i guess you should be good to hold whatever boost you trow at it with that 3 inch exaust and mbc

[mcglsr2]

Alright, thanks guys! Time for me to go remove the washers I have under the wastegate...