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Combined intake/exhaust manifold flange?
https://slantsix.org/forum/viewtopic.php?f=30&t=65080		 Page 1 of 1
Author:  SpaceFrank [ Tue Jul 07, 2020 8:18 am ]
Post subject:  Combined intake/exhaust manifold flange?
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:

Image

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.
Author:  Greg Ondayko [ Tue Jul 07, 2020 12:54 pm ]
Post subject:  Re: Combined intake/exhaust manifold flange?
I wonder if warping and vacuum / boost leak would be an issue?

Greg
Author:  SpaceFrank [ Tue Jul 07, 2020 3:07 pm ]
Post subject:  Re: Combined intake/exhaust manifold flange?
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.
Author:  Greg Ondayko [ Tue Jul 07, 2020 7:09 pm ]
Post subject:  Re: Combined intake/exhaust manifold flange?
Yes Frank,

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


Greg
Author:  Jase [ Thu Jul 09, 2020 11:28 am ]
Post subject:  Re: Combined intake/exhaust manifold flange?
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?
Author:  Dart270 [ Thu Jul 09, 2020 11:48 am ]
Post subject:  Re: Combined intake/exhaust manifold flange?
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.

Lou
Author:  Old6rodder [ Thu Jul 09, 2020 7:02 pm ]
Post subject:  Re: Combined intake/exhaust manifold flange?
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.
Author:  SpaceFrank [ Thu Jul 16, 2020 11:24 am ]
Post subject:  Re: Combined intake/exhaust manifold flange?
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...
Author:  SpaceFrank [ Tue Apr 27, 2021 11:32 am ]
Post subject:  Re: Combined intake/exhaust manifold flange?
As a follow-up... I ended up building a really ugly combination manifold with one these one-piece flanges. While I made a number of mistakes with this design (mainly prioritizing compactness over ease of installation), it didn't appear to have any issues with warping at the head surface. We used a standard Mahle/Victor-Reinz gasket, and it didn't show any signs of leakage when I removed the manifold after a few hours of hard running (dyno pulls and track testing at a Lemons race).

That being said, there was about 1/16" of curve in the flange surface after I was done welding. I couldn't find a machine shop that had both the fixturing and the desire to cut this monstrosity flat on short notice, so I ended up buying a 24" belt sander on Craigslist and spent a few hours getting it close enough.
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