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Twin External Wastegate setup

Posted: October 10th, 2006, 4:17 pm
by cantfindausername
I've been speaking with a friend of mne today about my rather large turbo, and rather small wastegate set up.

The turbo is a GT35R and the Wasteagate is a Tial 38mm unit.

He has planted the seed in my head about using twin wastegates to help control boost when I want it set low.

Has anyone ever come across something similar? Got previous experience with a similar setup, or even just a thought on the above?

I'd love to hear anyone's thoughts on this idea!



Here's a link to a nice photo of what I am talking about, avoids copyright issues associated with publishing it here: ... ount01.jpg

Posted: October 11th, 2006, 10:02 am
by Guy Croft

I imagine that in this installation there are two wastegates primarily to suit the architecture of the vehicle, two small ones rather than one large one, though there may be pressure-wave interference effects present in the pipes into the turbine housing that they are trying to avoid by splitting the wastegate systems. And naturally the response of two smaller units is faster than one big one, as the smaller the valve in the wastgate the better its discharge coefficient.


Posted: October 11th, 2006, 10:33 am
by cantfindausername
So are you saying that a twin (smaller) W/G setup would be a better choice than increasing the size of the single W/G setup?


Posted: October 11th, 2006, 10:44 am
by Guy Croft
Well, Ant, yes, certainly as far as the point re discharge is concerned, though how much of an issue that might be would I expect depend on the exhaust massflow and the criticality of the wastegate bypass response time.

There may be other issues - so I am open to correction. And of course the fitting of two wastegates rather than one wastegates has to suit your pipework, which it certainly does in your example (link).

If anyone has informed advice to offer, feel free.


Posted: October 11th, 2006, 11:19 am
by cantfindausername
I need to take some measurements really I think.

I love the idea of it and am goin to give it serious consideration. I will need work to be done either way, so figured I might as well go for something a little different to the MR2 norm.

Something I've tried to do as much as possible with this project. As with everything else, its a gamble, but could be one that pays off.

Thanks for your input Guy! Its always appreciated.


Posted: October 11th, 2006, 12:00 pm
by SteveNZ
A single 38mm wastegate with the right install will be adequate for a GT35 on low boost. They can work well right up to about 500BHP.

The only reason you would need twin wastegates in my view, would be to suit a twin scroll turbine housing. The headers would need to be perfectly tuned for each scroll though or there is no point.

If they are working close to their maximum, a larger wastegate with the right tune may get a bit more bhp out of it. But I would really not bother if its not creeping on 1.

Posted: October 11th, 2006, 12:19 pm
by SteveNZ
I just took a look at the photo and they look like Tial 44mm wastegates. Thats got to be made for show.

Posted: October 11th, 2006, 12:33 pm
by Guy Croft
Ade, could you write to the manufacturer and ask him why he has used two wastegates please?

Members - Avoid further ref to his product until such time as the vendor has commented himself please. If he does. He may not wish to.

This is quite imperative in every case where another's product is referred to, thanks. I know it's always interesting but..


Posted: October 14th, 2006, 10:48 pm
In my old turbo setups including the gt3540 (gt35r) I used 50mm single ext WG setups. Much better than 2 units and also cost effective. I also make a lot of experiments in my twin scroll applications and I also prefer one single 60mm for twin scroll hi boost engines (4cyl) .Be careful, to have very good balanced pipes going to WG and coming at the end of collector in single pipe setup .

Posted: October 16th, 2006, 8:23 pm
by Acki
Hmm a wastegate for each exhaust pulse is possible.