External wastegate through exhaust flange?

[Jpich85]

I've been researching about external wastegates and noticed that some people run the wastegate gas through the turbo then from the exhaust flange into the wastegate then through a separate pipe?

I've found that people remove the internal wastegate then weld a divider in the turbo housing then run two separate pipes from the exhaust flange one into a external wastegate and obviously the other is the exhaust pipe, 

I wanted to ask if this was a good set up compared to coming straight off the manifold?

Here's a picture of the set up

[Gixer1460]

You can't run ANY wastegate AFTER the gasses have passed through the turbo - it would achieve nothing, WG's need to be pre turbine to relive exhaust gases. Dividers will only be used with twin scroll turbines and will usually be used with twin WG's. Some high end builds even mount the gates directly off the scroll / s for best reaction / responses.

For the majority of builds internal gates can work ok but higher pressures / exh. flows benefit from use of external gates. Some of the commercially produced systems are works of art, developed over many years and simply copying the external appearance without knowing what's 'below the skin' can make a bad set up.

[Jpich85]

Thanks for clearing that up mate, I did think that the wastegate gas should come straight from the manifold, I've spoke to a few people and they all tell you different things sometimes so I'm just trying to make use of the different things I'm learning so far, I think I'll take off straight from the manifold then when I eventually get going on the bike. 

That's true 1460 I like to find out why things are like they are especially when it's something like a turbo because like you said just copying something without knowing how things work can make things worse for you. 

Thanks for clearing that up

[Jpich85]

Going from this picture, if you removed the internal wastegate and opened this flap up permanently, wouldn't the manifold gas just pass straight through the turbo then build up in the wastegate if you mounted it like I mentioned at the beginning of the thread.

I'm not sure how turbos are designed so maybe by the time it come out of this separate flap it's already passed through the turbo?

 

[Gixer1460]

Look where the flap valve is in relation to the incoming exhaust gases. A WG only needs to operate once required boost has been achieved and / or to stop the turbine overspeeding. Internal gates work but are crude due to asking the fast moving gas to turn 90 degrees an exit out to atmosphere and relieve exh. pressure. This is why external gates are positioned ideally on a tube that is on the gas flow path of least resistance - it gives better and more controllable response and less chance of boost creep / spikes.

That picture is similar to my 1st turbo - a Garrett T2 but its housing had a cast in divider to keep main 'used' exhaust away from the WG bleed off exhaust. I used to run a dump pipe and the WG small tube joined that about 4" from the flange face, good for 10psi and no creep.

[MeanBean49]

4 hours ago, Jpich85 said:

Going from this picture, if you removed the internal wastegate and opened this flap up permanently, wouldn't the manifold gas just pass straight through the turbo then build up in the wastegate if you mounted it like I mentioned at the beginning of the thread.

I'm not sure how turbos are designed so maybe by the time it come out of this separate flap it's already passed through the turbo?

 

In order to run an external wastegate with turbo housing like this, you can either weld the flap valve shut and put the wastegate into the headers, or weld the flap open, make a  seperator plate in the housing that seals against the exhaust flange and feeds into a seperate pipe with the wastegate in, like the pic you put up earlier.

That all being said at boost levels up to about 18psi ive never had a problem using a standard internal wastegate on either td04 or VF range turbos, i just change the actuators for adjustable ones for easy boost adjustment.

Big aftermarket turbos are a different kettle of fish

[Jpich85]

6 hours ago, MeanBean49 said:

In order to run an external wastegate with turbo housing like this, you can either weld the flap valve shut and put the wastegate into the headers, or weld the flap open, make a  seperator plate in the housing that seals against the exhaust flange and feeds into a seperate pipe with the wastegate in, like the pic you put up earlier.

That all being said at boost levels up to about 18psi ive never had a problem using a standard internal wastegate on either td04 or VF range turbos, i just change the actuators for adjustable ones for easy boost adjustment.

Big aftermarket turbos are a different kettle of fish

Thanks for the insight you guys, I appreciate your help, it's good to ask you lot as you've all had experience with this sort of thing and this is the only place I can really learn about things bike related, looking forward to getting started on this build now just need the new year to come round now