Midnight Caller Posted November 26, 2020 Report Share Posted November 26, 2020 Hello guys ! I've been searching on the forum but didn't find anything relevant information about my issue. On my S70 T5, I've acquired an "R" manifold, and ported it out a little at the collector. Went back home and tried to match it with the GT3071 turbo that's been waiting in the closet for the last 4 years The bolt pattern is a perfect match (the GT3071 was bought with a T3 flange hotside). But the hole in the T3 flange is almost square (corners rounded) and the output manifold port is round : T3 flange (square hole), the same as my turbo's "input" port : And my exhaust manifold : My question is - what do you guys do in this situation ? Won't the port mismatch lead to a back pressure because of the restriction caused by the shape difference ? How would you proceeed in such case ? Port the turbo housing hole ? I've only found a possible solution to this, meaningly an "adapter" flange for the shape difference, but I'm not convinced it would be the only way to do it : Thank you a lot ! Link to comment Share on other sites More sharing options...
Zappo Posted November 27, 2020 Report Share Posted November 27, 2020 I would avoid using the adapter if you can as it will put the turbo closer to the firewall. However, it is an easy solution to avoid machining off the raised ring of the exhaust manifold. Most people will machine the sealing ring flat and bolt on the turbo. It isn't going to cause a back pressure issue. Link to comment Share on other sites More sharing options...
Midnight Caller Posted November 29, 2020 Author Report Share Posted November 29, 2020 Hello Zapo ! Thank you for the quick reply ! No, I'm not going to use the adapter as that could also lead to extra risks of exhaust gases leaking out. I just posted it as an example of difference between the collector output and turbo inlet. I've already machined the lip on my "R manifold", but only after that I've read about losing the I'm thinking about the dynamics of the exhaust flow, where a round hole meets up with a square hole (wich has the lesser side smaller than the circle diameter) , and I'm thinking that some of the gasses will hit a "wall" and will be forced back into the exhaust manifold. Putting one over the other would look like this. My concern is the blacked out area (that in reality could even be bigger). Link to comment Share on other sites More sharing options...
Zappo Posted November 30, 2020 Report Share Posted November 30, 2020 You could trim the exhaust housing on the turbo to match it. The spacer does it, but you could do it on the housing itself. I never did it with mine though. Your back pressure is going to be more about the A/R of the exhaust housing on the turbo than the exhaust manifold port. Link to comment Share on other sites More sharing options...
NIOMARVIN83 Posted February 21, 2021 Report Share Posted February 21, 2021 Hello. I drilled and tapped my "stock" manifold for the T3 flange. I'm running my holset off a ported factory manifold. No issues at all. I in motor trader also checked the head-side of the manifold for straightness and found it to be seriously warped plus machined a new surface on the T3 mount side. Link to comment Share on other sites More sharing options...
Zappo Posted February 21, 2021 Report Share Posted February 21, 2021 1 hour ago, NIOMARVIN83 said: also checked the head-side of the manifold for straightness and found it to be seriously warped I would check this as well. I had the same issue for years but didn't know it. When I had my head gasket done a few months ago, they noticed the manifold was leaking at the head. Machined it flat again. Link to comment Share on other sites More sharing options...
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