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PostPosted: Tue Jul 07, 2020 8:18 am 
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Turbo EFI
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I went to eBay looking for that one guy who sells plasma-cut exhaust flanges, and in addition to his standard two-piece exhaust flanges for the slant six, he also has this thing:

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We've been talking about converting to MPFI in addition to building a dedicated turbo exhaust manifold, so this might be just the ticket for building our own compact intake as well. What are the downsides to having both manifolds permanently connected like this? Aside from the completed (mild steel) assembly weighing 40 pounds, I mean.

To minimize heat transfer to the intake, I would build the two manifolds as separate units aside from where they meet at the flange. I might add some support struts between the two halves, but I'd definitely plan to leave enough room to wrap the exhaust section.

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PostPosted: Tue Jul 07, 2020 12:54 pm 
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I wonder if warping and vacuum / boost leak would be an issue?

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PostPosted: Tue Jul 07, 2020 3:07 pm 
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Turbo EFI
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You would need to be very careful during fabrication to minimize warping of the flange. Clamp it down tight, weld small sections at a time to control heat buildup. Even then, I would budget a trip to the machine shop to have the mating surface cut flat afterwards.

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PostPosted: Tue Jul 07, 2020 7:09 pm 
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Yes Frank,

I meant when its running and put together, but I suppose there us the same concern during the fab stage too!


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PostPosted: Thu Jul 09, 2020 11:28 am 
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TBI Slant 6

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SpaceFrank wrote:
I What are the downsides to having both manifolds permanently connected like this?

To minimize heat transfer to the intake,


I would think that is the main issue/challenge...

What are the benefits of having it all linked together?


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PostPosted: Thu Jul 09, 2020 11:48 am 
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Yeah, I'm skeptical it can work in a situation where you have plenty of heat (like a turbo). Differential thermal expansion of intake and exhaust parts of the flange... I would not bother trying it myself, but I'm not saying it can't work.

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PostPosted: Thu Jul 09, 2020 7:02 pm 
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Turbo Slant 6
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I tend to work with temp flex rather than fighting it, so use the multi piece flange set on my HAMBtser, and a long runner cast aluminum intake on my Toad. Planning on a brace of Dutras on 'Toad's exhaust when coinage permits.
Even more so on a Buick str8 I'm presently doing.

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PostPosted: Thu Jul 16, 2020 11:24 am 
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Turbo EFI
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So the main thing I want to do in the short term is build a compact exhaust manifold that goes from the head to a single T3 turbo flange. I'm worried that if I use these two separate exhaust flanges at the cylinder head, that it'll tend to warp over time and bring the two halves out of alignment. I know the original one-piece exhaust manifolds tend to warp in a way that curves the ends inward, but the manifold I'm building would be different in a couple ways. First it's steel tubing vs. heavy cast iron, and also the two groups of ports will be tied together at each flange (3 and 3). I'm not sure if this will make it more or less likely to warp. If it helps, I could also combine the two flanges in the center by looping some narrow bar stock around the center two intake runners. If anyone here has built a dedicated slant turbo manifold, I'd love to see pictures of what you came up with.

As for the manifold with both intake and exhaust ports, I agree it would see high temperature fluctuation across the flange, but I'm not sure what mechanical behavior that would induce. Part of me thinks it would want to turn into a pretzel, the other thinks it would be more stable than a one-piece exhaust manifold. Too bad I don't have access to ANSYS anymore...

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