Purpose benefit of external waste gate

dangerous06

dangerous06

diesel tech
Joined
Mar 24, 2008
Messages
3,564
I've seen a lot of exhaust manifolds with cast in mounts for waste gates. What is the purpose of these? When would it be needed? What would you want to set them at? What size and how do you figure that out? I've seen sizes from 30 to 60!
While on the subject what's with the pop off valve on the intake side does this help save the turbo on full to no pedal? How do you figure size and set up?
 
dangerous06 said:
I've seen a lot of exhaust manifolds with cast in mounts for waste gates. What is the purpose of these? to divert exhaust away from the turbine wheel, which in-turn slows the compressor, which limits/regulates boost
When would it be needed? anytime you want to regulate boost or drive pressure
What would you want to set them at? whatever boost/drive is appropriate for your setup
What size and how do you figure that out? good question. I don't know how to calculate size, but it will certainly take into account the volume of air you will be working withI've seen sizes from 30 to 60!
While on the subject what's with the pop off valve on the intake side does this help save the turbo on full to no pedal? How do you figure size and set up?
Click to expand...
pop off valves are a cheap and semi effective eay of relieving boost pressure spikes. A throttle pedal referenced blow off valve is what you'd need to save the turbo from barking after letting out of the throttle

A search would lead you to much more detailed answers.
 
So a turbo with a waste gate is enough? Or is there a time when more is needed such as when using Nitrous?
As far as where to set max boost that seems a mystery? I thought it's set by fuel.
 
jlibert said:
pop off valves are a cheap and semi effective way of relieving boost pressure spikes.
Click to expand...

THIS IS BAD INFORMATION!!!

Pop off valves cause compressor overspeed and turbo failures. DO NOT USE!!! It is the same as adding a boost leak to the system, at high boost pressure.

These are different from a Blow off valve, that opens when the throttle has been released to prevent air from backing up against a rapidly slowing compressor wheel to avoid having it stall.
 
Last edited:
Also, pop offs have a side benefit of failing open as well.

Sent from my SCH-I545 using Tapatalk
 
OK So a S300 waste gate will need what size additional waste gate to run NOS safely? Then what would you set the relief pressure at? What would be max safe boost?
 
The purpose of external wastegate it is to bypass the secondary turbo's turbine housing. The primary turbo will flow more air than the secondary turbo's turbine housing can flow which will cause a high drive pressure at the manifold. The external waste gate allows the drive pressure to bypass the secondary turbo's turbine housing and help drive the primary turbo. External waste gates are also used to bypass non gated single turbos. IIRC
 
dangerous06 said:
OK So a S300 waste gate will need what size additional waste gate to run NOS safely? Then what would you set the relief pressure at? What would be max safe boost?
Click to expand...

Depends on How much fuel and spray you are using, along with internal gate size and Turbo size. A drive pressure gauge would tell you very quickly if you needed a larger gate.

phone
 
Its not really to bypass the turbine as it is to properly keep drive pressure in check, it will all depend on the setup and turbo sizes, the primary may need to be gated as well.
 
The purpose is to limit shaft rpm to either keep the compressor and turbine wheels close to peak efficiency or to limit shaft rpm to keep the turbo from exploding, depending on what you are going for.

The benefits of an external gate are:
-Flow
-Range of adjustment
-Durability
-Ease of setup / adjustment

The benefits of an internal gate are:
-Ease of installation
 
dvst8r said:
The purpose is to limit shaft rpm to either keep the compressor and turbine wheels close to peak efficiency or to limit shaft rpm to keep the turbo from exploding, depending on what you are going for.

The benefits of an external gate are:
-Flow
-Range of adjustment
-Durability
-Ease of setup / adjustment

The benefits of an internal gate are:
-Ease of installation
Click to expand...


Best answer yet!
 
dvst8r said:
THIS IS BAD INFORMATION!!!

Pop off valves cause compressor overspeed and turbo failures. DO NOT USE!!! It is the same as adding a boost leak to the system, at high boost pressure.

These are different from a Blow off valve, that opens when the throttle has been released to prevent air from backing up against a rapidly slowing compressor wheel to avoid having it stall.
Click to expand...

How is it bad information? Does it not do exactly what i said? Keep in mind that i never advocated using them, even though many twin turbo kits come plumbed this way.
 
jlibert said:
How is it bad information? Does it not do exactly what i said? Keep in mind that i never advocated using them, even though many twin turbo kits come plumbed this way.
Click to expand...

In reality, despite as you say they come on many turbo kits, I have yet to see them work as "advertised". From what I have seen they either fail to open, or are open all the time. They were a gimmick to prey on the naive diesel owner into making them think this would "save" their head gaskets or engines ect... So that it was "safe" to run twins.

I have yet to have hurt a diesel with a boost spike... Excessive fuel or timing sure, boost no.
 
Any suggestions on make and size and how to set? Found plenty of tail go ahead jokes will fly.......... OK Tial 38mm 45mm 50mm?
 
JGS50mm, run regulated drive pressure to the top, and then non regulated to the bottom. Play with a compressor to see what pressure over comes the spring.
 
We run a JGS50mm as well, but I have run Tial several times in the past, they are good gates too.

Unlike turbo's it is better to have too much gate than too little. With that being said unless you are spraying a bunch you won't need a ton of gate.
 
I doubt you'll need more than a 38mm, it can flow a boat load of mass for a street/strip truck.

One of the biggest things about gating for me was more control over air/fuel mixture. Without the gate I was running quite lean since I had to pull the pump back to prevent turbo overspeed. Since then I'm running about the same boost but the truck has picked up 125 hp from throwing more fuel at it at the same boost.
 
You must log in or register to reply here.
Back
Top