Project S2000: Part 29 – Investment Cast 347SS Turbo Manifold

I scribed out a line that the Dykem makes easily visible to mark the limit of where I wanted to grind.

This is part of the way through the process of removing the material that would create a step into the flow. I used the carbide cutting bit first followed by the grinding bit. I used a garbage can as my work bench. My home garage shop only has the best work benches.

After the cutting and grinding bits, I followed up with the flap wheel. I figure this is about 25%-50% the benefit of doing extrude hone for about 10% of the cost. The goal of course is to reduce surface roughness to reduce flow losses which translates into faster turbo response and more power. The raw surface roughness of the investment cast part from Invest Cast was quite good; I’d guesstimate about half the roughness of your typical sand cast manifold or turbine housing. But while I was in there grinding, it was little additional effort to improve the surface finish some more.

For reference, this is the untouched inner runner of the one extra manifold Invest Cast made. On a project like this, it’s often tough to get it right the first time, so they made two.

I used the flap wheel as far as I could into the runners and the merge collector. You can see where I wasn’t able to reach in the middle of the runners where it looks less shiny.

This is the view into the merge collector from the wastegate port. Hopefully there’s enough wastegate flow. It’s a good thing the Mahle pistons are 9.5 compression ratio so we can run a lot of boost on pump gas regardless.


  1. It’s good to finally see the finished casting! Thanks for showing the small changes as you went forward with the design iterations- getting all those critical measurements to line up all at once is a pain.

    Can’t wait to see/feel it in person. 😉

  2. Oh man, I’ve been waiting for this article, and even harassed you a bit on instagram when you posted a teaser. Over the last few years I’ve been getting really into 3D scanning and 3D printing to augment my solidworks design workflow, and its crazy how far the technology has progressed. I’ve really enjoyed both parts of this turbo design and seeing your process Its too bad that there isn’t a low cost support option for the metal 3D printing. I guess either way you’d still have to remove all of the supports and smooth it all out.

    My company was also recently approached by a company that offers a 3D printer that can print sand cast molds, and though of how useful it could be for small projects like this.

    1. Check out this video from Papadakis Racing where they just did a 3d printed Inconel manifold. At 6:56, you can see them knocking out the support material. The whole video on how they did the manifold design is a better version of how I did it. Our buddy Tyler is the guy doing the 3D scanning in the video. I wish I would have had a full scanner like that and scan the whole engine bay. Better than working off of pictures and tape measure and caliper measurements. It basically saves one iteration.

      1. Just looked at the Papadaski printed manifold, don’t understand why that are not looking at the rx and circuit racing manifolds, those cars run for years this. We run it on our car with grate success but the design of assbly is way different. Also it’s just stupid to leave out the free air injection from the design,it’s a turbó engine,in the 80s engineers knew it’s a must.

  3. ok so I mostly don’t know what I’m talking about on the subject… but don’t you want cuts on the flange between the runners so the manifold has space to expand and contract with temp changes?

    1. On a 4-cylinder, typically the manifold is short enough. On an inline-6 though, it’ll be often split 3 and 3. Also check out the manifold from the BMW B58 engine where they stick bellows joints between the runners on their log manifolds to prevent cracking. On long log manifolds, there needs to be some type of bellows or slip joint. On tubular, the tubes can bend a bit like a paperclip. Another reason for the larger 9.15mm bolt holes in the flange are to allow for some of that expansion/contraction.

    1. I have the one extra and that’s it. If you’re interested, hit us up; it’s not going to be cheap though. I want to get my car running first to see how it does before selling the spare so I can make sure the buyer knows what goes into fitment and also the boost performance.

      1. How much would it cost to produce another one of these manifolds? I would be interested as well. I know you said it was not cheap but if the process has already been proven… God bless.

        Thanks again.

        1. After I test out the performance and the minimum level of boost it can run, I may consider having a handful made if there is enough interesting. I expect to have everything up and running by summer. If I can get the piece price down below $3k and enough people signed up, we could do it.

          1. How do I get on the list for this manifold? Idk why it has taken so long for someone to make a high-performance cast manifold for the s2k.

        1. I paid a LOT for it. One-off prototypes are not cheap. The manifold by itself cost almost as much as a Full-Race or SOS TSMAX turbo kit. This included the casting, heat treatment, and machining of the manifold. And keep in mind, the quote I got for the casting from Invest Cast was 3x cheaper than the other supplier!

  4. There is so much hardcore geeking out going on here, I love it.

    I had to look it up in your past articles, but you should also have linked those for reference as to how you got to this point. It was a good re-read for me.

    1. Thanks for the feedback! I typically do link, but just didn’t this time. I went back and added a iink to Part 25 when this whole hairbrained idea started almost 3 years ago!

  5. I think it’s a super cool project and I love spending money but I just don’t get the aversion to just welding one up out of tube unless the only goal was to fool CA smog techs. Just seems like a huge expense for something like this, then you go and cover it up with a heat shield?

    1. Doing it as a casting gives a lot more design freedoms. Like I was able to do a pretty gentle transition from the oval head port geometry to circular runner to minimize flow separation. And I was able to make the merge quite compact. The runners are all splines in shape instead of constant radius bends, so that gives some more freedoms with infinitely different radii. In hindsight, I could have made the wastegate runner port even bigger than the 4mm I did over the WG flange. Also, every weld joint is a potential failure point. I probably could have designed it as a fabricated manifold and it probably would have cost as much being a one-off as jigs would have had to be built, all the cut sections required, the merge would have been a pain in the ass to fab, etc. The reason for keeping the stock heat shield is thermal management to improve reliability.

  6. I would love to see a youtube video about this and future updates to the s2k! especially with Mike Kojima as the host!

  7. Hi Khiem,
    I’m looking to buy manifold.
    Also sent you message on Linkedin.

    I can’t find where to get manifold to my s2k with g25-660.

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