External Waste Gate

[AlanG]

I see - but the other parts of the question... do bigger turbos come without the internal gate meaning that only the external gate can be used?

yes

[AlanG]

i think its a waste of time and money but some boys from the US of A do it!

I agree. Why would you want to go external with a turbo which has an internal one? If you've got problems with the internal 'gated turbo, then the problem lies elsewhere.

[AlanG]

There's more to my previous answer John,but i didn't want to confuse any further! You can sometimes see circumstances where the exhaust gas pressure into the turbo is so great that it can also open the wastegate, but the idea is that it's boost pressure which controls when the wastegate does and doesn't open.

[thewelsho]

There's more to my previous answer John,but i didn't want to confuse any further! You can sometimes see circumstances where the exhaust gas pressure into the turbo is so great that it can also open the wastegate, but the idea is that it's boost pressure which controls when the wastegate does and doesn't open.

So, thinking back to some problems experienced by other users on this forum stating that they are not hitting peak boost and some of the answers talking about the actuator arm; does this then mean that the w/g is lodged open thus dumping all of the pressure (or prevents pressure build-up), which in turn stops the impeller from spinning? Also, the execessive pressure that goes out the wastegate, were does it go?

[fai17]

So, thinking back to some problems experienced by other users on this forum stating that they are not hitting peak boost and some of the answers talking about the actuator arm; does this then mean that the w/g is lodged open thus dumping all of the pressure (or prevents pressure build-up), which in turn stops the impeller from spinning? Also, the execessive pressure that goes out the wastegate, were does it go?

yes it can be and execessive pressure goes down your downpipe....

[st3ph3n]

John, with your setup the gasses that bypass the impeller via the wastegate and end up in the same downpipe.

If you look at this one I believe you can see the large opening for the gasses coming through the impeller, and the smaller one for the wastegate:

With an external wastegate you can run a second exhuast pipe where the gasses that bypass will exit, or you can plumb it back into your existing setup.

[AlanG]

this then mean that the w/g is lodged open thus dumping all of the pressure (or prevents pressure build-up), which in turn stops the impeller from spinning?

That's it John.

The exhaust gasses naturally want to go through the turbine housing, through the exhaust wheel and then through the downpipe and out the exhaust. With the wastegate open you give an alternative route for the exhaust gasses to go through, hence less pressure through the exhaust wheel and hence less boost pressure created by the compressor side.

Back in the late 90's early 00's, there was work done on the exhaust housings of some turbo's and downpipes in trying to keep the wastegate gasses separate from the exhaust gasses, as some turbos when the wastegate opens, causes those gasses to run straight into the path of the exhaust wheel gasses and can limit potential output.

You may have seen some downpipes with splitters in them. This was designed to ensure no turbulence from the exhaust wheel of the turbo.

[AlanG]

Also, the execessive pressure that goes out the wastegate, were does it go?

In terms of external wastegate, you have the choice of an open pipe (called a screamer pipe) or return back into downpipe.

My preference is to return because of noise issues cause if you think about it, those exhaust gasses leaving a screamer pipe is basically an open ended exhaust with no silencer.

I did try the first set-up with a screamer pipe cause i wanted to run the car and was too lazy at the time to do the pipework to return to downpipe and it was very loud when on boost. It also gave a lot of vibration through the floor under my feet which also made it sound like someone was having a great big fart!

Edited May 8, 2008 by AlanG

[st3ph3n]

So is boost creep caused because the wastegate isn't efficient enough when fully open to bypass enough of the gasses?

[thewelsho]

So is boost creep caused because the wastegate isn't efficient enough when fully open to bypass enough of the gasses?

I need to read this whole thread again with my spare turbo in front of me! Since I finish at 1 and its a lovely day, I'll print this off and sit on the decking with the print and turbo - yeeee ha!!! LOL!

[AlanG]

So is boost creep caused because the wastegate isn't efficient enough when fully open to bypass enough of the gasses?

Yes.

Edited May 8, 2008 by AlanG