Made progress on the turbine exit. This a tricky spot as there's very limited space. I was trying to keep it from needing to be 3D printed as this is going to get expensive fast...but alas, the 3D printed part will work far better.

The turbine exit necks down from 3" to 2.5" while curving toward the muffler and away from the chassis. The 02 sensor was tough to fit, but I think it will work okay. Bosch recommends at least 10 degrees from horizontal and this is 20 degrees.

The turbine exit also incorporates the wastegate entry. I did my best to get the gasses flowing in the same direction even though there was limited space and it's coming in at a right angle. I still think this is the ideal wastegate location....a nice direct flow and very compact.

Unfortunately, the turbo size and location requires that I cut the chassis some. I tried to avoid it but this is the best compromise I can come up with. The section that needs to be cut is just thin steel that supports the tow hook. I'll probably end up welding on some reinforcements after I cut to clear the turbo.

Next up is designing the turbo mounting bracket and the compressor outlet plumbing. Turns out there's not enough room in the front of the wheel well for the water to air intercooler core so it will be located in the engine bay.

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I like to 3D print as I work through a design. Seeing things in person often reveals unexpected issues and opportunities. It’s also nice to get out of the computer!

I’m running 2.5” OD tubing (sometimes round and other times not but of equivalent cross sectional area) from the headers to the turbo. Anyone know what the 930 used? I think 2.5” might be overkill.

The compressor housing is not clocked correctly yet. Will do that once I start work on that plumbing.

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I love the way you seamlessly cane back to the exhaust outlet. Nice design.

Very nice build, good luck with that.

I was wondering what type of material you were planning on making the end tanks out of that you were going to have 3-D printed. I know there’s not a lot of good resins or fillaments available for high temperature, that can be printed on lesser expensive machines.

3d print metal and weld.

There's actually some really good high heat plastics available now. I just switched over to Bambu for my 3D printer and they have some great stuff that's dialed in. I can either use their PAHT-CF (Nylon that's good up to 375 F) or their PPA-CF (crazy strong nylon good up to 425 F). The PAHT-CF is far less expensive so I'll probably go that route.

I plan on 3D printing all off the non-exhaust plumbing in plastic. I'm also hoping to 3D print the intercooler end tanks in plastic. That really depends on whether or not I can bend the locking tabs out to remove the old end tanks and back again to hold the new ones. They are aluminum so they are not going to love the bending...

I have also been using the PAHT-CF and PA6 -CF30 with great results. I always wonder about their porosity as filament printed parts, rather than SLA parts though.

I wouldn't put the O2 sensor on the pressure side of the turbo

Moparrob I have found the parts to be just about air tight, but I’ve thought about painting them with epoxy resin to seal them and add strength. I think I’m going to go with 2mm walls so these parts will be really stout and air tight enough. I will need a bond a lot of parts and hoping I can find a good glue for nylon.

Flightlead404, agreed. It’s currently located just after the turbo. I will add an EGT sensor on the pressure side before the turbo, probably in the Y pipe.

I have to say that this exercise has made me wish I could run twin turbos. The current exhaust routing is far from optimal. The exhaust travels like 5 feet before it reaches the turbo. Not great for lag and also delays the O2 sensor reading. The 996 and later turbo setup is quite nice in terms of packaging and efficiency. Minimal exhaust and intake plumbing length.

Here's how the charge pipe is shaping up. This enters into the engine bay in a good spot and provides a straight shot to the intercooler and then the throttle body. I think this is a much better solution than trying to go straight up through the engine tin. The fit would have been so tight that it would have required compromises to flow and serviceability.

To keep it from getting damaged in this location I'll need to either make it very thick plastic or add some kind of shielding. It will be connected to the turbo with a hump hose to allow for some flex.

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That's a great scan

I received my first stainless 3D print. I’m pretty amazed at the quality, especially given the price. The cost was $45 delivered from China using CraftCloud. Many of the exhaust parts will be printed by the same process. They will be much larger so there’s a lot more risk of warping, but this is a good start.

This is the low profile turbo drain I designed to (hopefully) allow me to drain into the lower rocker cover and not use a scavenging pump.

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Photo of the drain on the turbo

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I’ve also been trying to find the best intercooler solution. I know I’m going water to air and I know it will be mounted on top of the intake manifold. I’d also like to use an OE intercooler because I generally think they are better engineered and the plastic end tank design will allow me to easily print my own end tanks.

Smaller is better for packaging and engine bay aesthetics, but of course smaller comes at the expense of performance. The two I’ve narrowed down to are the intercooler from a BMW M4 and a Mercedes C43 (previous generation twin turbo V6 version).

The BMW intercooler is much larger but that engine also makes a ton of power (480 hp I think). Both engines are 3 liter so the flow rate will be very similar to this application. I assumed both would have minimal pressure drop…but I was wrong…

To test this I’m using a 12A electric leaf blower. First I figured out then flow rate at various back pressures for the leaf blower using an homemade orifice flow meter. The blower has two power setting so there are two curves.

Then I measuring the pressure drop across the intercooler and lo and behold, the conveniently small Mercedes intercooler is quite bad. It has twice the restriction of the BMW. The blower does not flow as much as the engine but it does show about 0.5 psi drop at a flow rate equivalent to 4000 rpm. These things are not linear and I’d guess that would equate to something like 1.5 to 2 psi at full tilt.

The reality is that both would work okay. An extra psi or so of pressure drop is not huge. I think both would cool the charge air adequately as it just won’t be all that hot at these low boost levels. At the end of the day it would bug me to know I had a better option and the BMW intercooler still fits in the allowable space. So, for now, I’m designing around the BMW intercooler.

I also tested the muffler I plan to use (Magnaflow 14210) and it measure almost no pressure drop. Nice to know…


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Very interesting project. We are just finishing up the engine for my '87 Carrera and worked with Todd at Protomotive on the parts for a twin turbo conversion. Got it all in and only had to removed the rear tow hooks but it's tight. Reused the factory motronic and converted it to a MAF system. Finished the dyno tuning last month and are now working on the chassis to accommodate the engine.

Engine way out performed my expectations so, pretty excited to get the car back on the street. Good luck with the project and looking forward to reading more about your progress!

Just found the thread on your build. Incredible!

I said it earlier in this thread, but the engine and car really lends itself to a twin turbo setup. It just fits better…and of course offers better response.

Can't wait to see the new setup you're building.

Made some progress on the charge piping and intercooler. After finalizing on the BMW intercooler core based on the flow data, I started the end tank design.

The “in” end tank is pretty straightforward. The “out” side was complex to model. This connects rigidly to the drive by wire throttle body. Hopefully the plastic will be strong and compliant enough for this to work. I made it with very beefy 3.5mm walls. 3.5mm of carbon reinforced nylon should be really strong! I created a pocket for the DBW throttle body which I really like. It has a minimal impact on flow and looks well integrated.

The charge pipe that goes from the turbo to the intercooler is currently one piece. I need to do some more work to see it could actually be installed as once piece. It will connect to the intercooler using a 2.5” Wiggins style clamp (in black!). I think that style clamp plus the long plastic pipe will provide plenty of compliance. It will connect to the turbo using a bump silicone hose.

Lastly, I flow tested the intercooler with the custom end tanks on and it flowed just about the same as it did with the BMW end tanks. I’d guess back pressure will peak at something like 0.5 psi…extremely low.

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Wow, that is coming along really nicely. The end tanks look very nice and should work well in a CF reinforced PP filament- super strong. How will you bond the end tanks to the BMW core?

Are you using the 74mm throttle body off the 996/997?

Will the water reservoir and pump for the intercooler fit in the rear fender well?

Awesome build.

This is so cool!

Thanks guys!

The end tanks will be held on the same way the original ones were held on. There’s an aluminum edge that bends around a lip on the end tank. I bent this lip up to get the old tanks off and will bend them back when I have the final tanks complete. To get the air tight seal there’s a rubber gasket between the end tank and the intercooler core. I’ll add a little RTV on final assembly.

Yes, I’m using the 997 throttle body. Got the DBW pedal and bracket form Turbo Kraft. Really nice part and Chris has been great to talk to. So much experience!

The radiator for the intercooler is going to go in the front of the drivers side wheel well. I did’t want to run such long hoses but I think that’s the best spot. The pump will go there too. I bought a Pierburg CWA100 which is a monster intercooler pump.

Not sure about the reservoir location. It should be the highest point in the system but that’s not easy given how high the intercooler sits.



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