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

Looking first at the runner ports relative to the manifold gasket, you can see they are off a bit. Part of that is due to the aforementioned machining order of operations. The second reason they are off are due to casting tolerances. With investment casting, the tolerance depends on the size of the part which I believe is due to shrinkage of the part as it cools after casting. So, the bigger the part, the greater the absolute value of the tolerance. For investment casting, +/-0.75% is a typical tolerance. Each supplier can provide more exact tolerances for their given processes. If one were to go into Production, the casting model would be adjusted to account for the observed deviations in the first run in order to have as perfect of a casting as possible.

Here you can see the size of the exhaust port in the head of the engine relative to the manifold gasket. The offset is about 3.5mm.

I designed the ports about 1mm larger in size than the ports in the head because you never want a step inward into the flow. You don’t want a step too big outward either, but that’s still much preferable to an inward step into the flow. But with the casting tolerance, I was off about 1.5mm or so. To help with working the ports larger, I used some blue Dykem to paint out the differences between the gasket and manifold ports.

After applying Dykem, I used a pointy scribe to outline the difference in bolt hole location. The two outermost bolt hole locations being off was strictly my fault for taking a poor measurement.

I used a grinding bit in my Dremel with the router head on it to work the hole larger. This is me part of the way there in enlarging the hole.

My basic tools: eye protection (metal slivers in eyes suck), mask (breathing metal powder sucks), gloves (metal splinters suck), head lamp to see what I was doing, and my trusty Dremel with metal cutting bit, grinding bit, and a flap wheel. Not shown: noise isolating ear buds which are dual purpose for blocking out the loud grinding noise and listening to some music at a low volume. Because losing hearing sucks.


  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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