setting up a wastegate in compounds

[oldbluef250]

I have read several threads on using an external wastegate on a single setup, but how do you do it on compounds? Do you regulate it with back pressure or boost? and when a wastegate starts to open at lets say 15psi with a certain spring, how much is it actually releasing when it is fully open?

 

[Pizza pig]

Why 15 psi? It really depends on the setup to know when to let the gate start opening. A lot of people running compounds dump the gate into the low pressure exhaust piping to help with spool up of the low pressure charger.

Honestly tuning a wastegate could get to be a pain, a lot of setups dont even need an external gate, what about nitrous? Wastegates are to control backpressure, so its not boost related thats a blow off valve.

 

[oldbluef250]

15psi was just an example. And it would be plumbed in so the exhaust would get rerouted back to the low pressure turbo. I know i want equal amount of boost from both turbos. So if im making 60 lbs of boost, i want 30lbs coming from the low pressure, and 30 lbs coming from the high pressure. The setup is 215/150 injectors and s480/s362 turbos. I have a 46mm wastegate. I want a wastegate so i don't grenade the high pressure turbo from too much back pressure

 

[MorganY]

I run boost on top and bottom of the gate, run an inline reg on the top feed.

 

[STROKEDOUT]

opcorn: sub'd

 

[Cutting-Edge Diesel]

Put the 25.7 spring set up in It and set it up like this.

 

[Extended Power]

15psi was just an example. And it would be plumbed in so the exhaust would get rerouted back to the low pressure turbo. I know i want equal amount of boost from both turbos. So if im making 60 lbs of boost, i want 30lbs coming from the low pressure, and 30 lbs coming from the high pressure. The setup is 215/150 injectors and s480/s362 turbos. I have a 46mm wastegate. I want a wastegate so i don't grenade the high pressure turbo from too much back pressure

The HP turbo will not grenade from high back pressure...
Think about it.
The exhaust from the HP turbo is no longer going out to the atmosphere. (0 positive pressure)
It is feeding the primary...and it takes heat, volume, and pressure to drive the primary.
So, for an example, say you have 100 psi drive pressure going into the HP turbo, and on the outlet of the exhaust, you had 50 psi...that is only a 50 psi differential across the HP turbo.

If it was a single turbo application, and had the same 100 psi drive into the turbo, and it was going straight out the exhaust...now you have pretty much the full 100 psi differential across the turbo. (minus whatever is consumed from the turbo to drive it.)

The better flow you can get through the entire engine, manifolds, turbo piping, intake etc, makes for a far more efficient system overall.

 

[oldbluef250]

The HP turbo will not grenade from high back pressure...
Think about it.
The exhaust from the HP turbo is no longer going out to the atmosphere. (0 positive pressure)
It is feeding the primary...and it takes heat, volume, and pressure to drive the primary.
So, for an example, say you have 100 psi drive pressure going into the HP turbo, and on the outlet of the exhaust, you had 50 psi...that is only a 50 psi differential across the HP turbo.

If it was a single turbo application, and had the same 100 psi drive into the turbo, and it was going straight out the exhaust...now you have pretty much the full 100 psi differential across the turbo. (minus whatever is consumed from the turbo to drive it.)

The better flow you can get through the entire engine, manifolds, turbo piping, intake etc, makes for a far more efficient system overall.

So you don't think i need a wastegate at all?

 

[Extended Power]

If the turbos are sized 100% perfectly...then no, you shouldn't need a gate at all.

 

[Extended Power]

Put the 25.7 spring set up in It and set it up like this.

Using this picture...if you were running compound turbos...if you have 100 psi drive pressure to the secondary, the same 100psi would be acting on the bottom of the gate as well.
So if you had full boost pressure, say 65psi, going to the bottom port, and regulated the boost going to the top port...

Would you not have 165psi trying to open the gate, and a MAXIMUM of only 65 psi + the spring pressure inside the gate, holding it shut?

 

[Extended Power]

Damn...forgot about the pressure inside the outlet of the wastegate.

So if there was 100psi drive pressure, and say 50psi inside the hot pipe between the turbos, there would only be 50 psi trying to open the gate...

 

[Cutting-Edge Diesel]

Using this picture...if you were running compound turbos...if you have 100 psi drive pressure to the secondary, the same 100psi would be acting on the bottom of the gate as well.
So if you had full boost pressure, say 65psi, going to the bottom port, and regulated the boost going to the top port...

Would you not have 165psi trying to open the gate, and a MAXIMUM of only 65 psi + the spring pressure inside the gate, holding it shut?

you would also have the springs helping to hold it shut.. but if you had 100psi of back pressure and 65psi of boost i dang sure want my gate to open haha

 

[Extended Power]

you would also have the springs helping to hold it shut.. but if you had 100psi of back pressure and 65psi of boost i dang sure want my gate to open haha

Yup....that's why I'm driving it like a puss.

I got the "heavy" 7 psi spring in it, so I will need to put the boost to the top port only, and leave the bottom port open.
Then use a reg to dial it in.

May try to build a nice bench test/setup to get it dialed in before it even on the engine.

...too bad about the ceramic coating...oh well....I'll just wrap it all up...

 

[Cutting-Edge Diesel]

Yup....that's why I'm driving it like a puss.

I got the "heavy" 7 psi spring in it, so I will need to put the boost to the top port only, and leave the bottom port open.
Then use a reg to dial it in.

May try to build a nice bench test/setup to get it dialed in before it even on the engine.

...too bad about the ceramic coating...oh well....I'll just wrap it all up...

I ran the most spring I could in mine. came up to 25.7 psi