# Flyin' Miata NA/NB Turbo Manifold and Turbine Outlet Design

> Our original FM turbo manifold and outlet have been around for a really long time and have always worked really well. But we subscribe to the continuous...

Source: https://help.flyinmiata.com/en_us/boost-by-design-SyimjRCFa

Last updated: 2025-10-24T22:07:33.368Z

  

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Our original FM turbo manifold and turbine outlet have been around for a really long time and have always worked quite well.  But we subscribe to the “continuous improvement” idea, so when it came time to switch foundries (to improve product availability), we took that opportunity to make the new parts as good as possible.  We wanted to maintain the turbo location - partially because it’s a proven design and partially because the new manifold would be backward-compatible with pre-existing kits - so that established the hard points that we needed to work with.  From there, the world was our proverbial oyster. 

  

Within the footprint that we were held to, we wanted the best flow and lightest weight possible.  We investigated exotic materials, but after talking to materials experts, we decided that for our purposes, anything more exotic than ductile cast iron would’ve made it more expensive but not necessarily much better, so we chose to keep the price reasonable.  In order to keep the parts looking brand new for as long as possible, both our new turbo manifold and turbine outlet are coated in Cerakote, specifically the Cerakote C-7900 in their Glacier Titanium color.  This coating can handle exhaust gas temperatures up to 1,800°F and won’t fail if thermally shocked by dumping the parts in water from that temperature - although we don’t recommend that!  Also, while it's not scratch-proof, it is surprisingly scratch-resistant, far more than other coatings we’ve used.  After over a year of track and street use, our prototypes still look brand new. 

  

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## Ooooh!  Colorful spaghetti!

  

To get the best flow possible, we hired experts in computational fluid dynamics (CFD).  That kind of testing - at a professional level, not the DIY option - isn’t cheap, so after discussions with them, we had them model the exhaust flow inside our 1.8L turbo manifold in two adjacent cylinders, as that got us 90% of a complete manifold model for 50% of the cost.  That showed us where the flow was getting disturbed and, therefore, where it could be improved.  You can see in the CFD streamline image below that features the previous version of our 1.8L turbo manifold, that the airflow was disturbed at sharp angles on the outside runners (#1 and #4).  Runners #2 and #3 (the shorter, inside runners) were much better but could still be improved upon. 

  

![](https://lh7-us.googleusercontent.com/xtmYqfG5VqUpW9QOtmPKLewhrn3nFlZtHSqh5lk-Cln6zt3cPvhutVedpCt36Dfq9RYEz8tqpT7Idl84Zbbik0exjTZrfYT3NhSF65ybfKgthIw0HZq5dFg8XhxIAwihhNQePAZLrPJgCbLD29DXGVQ)

  

Armed with this knowledge, our CFD pros got to work.  First, they addressed the sharp angles as much as possible so everything flowed together nicely, which resulted in a 17% improvement in efficiency.  

  

![](https://lh7-us.googleusercontent.com/j02ByULMapswjN0-eQbOkyUvKPeVsOG68LGf-IihTo1-LY9uUzS5PLBKvOGkEETyoFDN21UOq1Agebs2Yk1rUwqpft5DzKE2BEWyTBQkZHWhTjNRJmxVoZIOV_Wn0QUgQ0mV_eoNszIW01wCIP_aAzA)

  

But they didn’t stop there!  What if we pointed the exhaust flow more directly at the turbo, at the expense of sharper angles in the runners?  That helped, but it was only an 8% improvement.  Bigger inside diameter on the runners?  It was a bit better, too, but that was still only a 15% improvement.  What if we play with diameters to slow down the flow on the shorter runners (#2 and #3) so that the flow from those runners takes closer to the same amount of time to get to the turbo inlet?  That netted us an overall **24% improvement in efficiency**, which is pretty huge.  In a real-world application, these efficiency improvements result in quicker spool and less backpressure between the exhaust ports of the engine and the turbocharger.  Check out how smooth that CFD is:

  

![](https://lh7-us.googleusercontent.com/mVJwvOmd5hKohqgSw4rTq1W_Vm0677nmWp9-7cSTy5bjFnRDht4eiLQ3VXYILrjg-k3E72l7V5VKSr49Bx6i2CxB2RCMHq85QuYmZHAB-cEbczKbo-6hWSh0DMczCJA43VNlQHUUPaNPLx117U7ByGo)

  

Put all together (graphically, this is two runners x2 as opposed to a CFD calculation of four runners); our new 1.8L turbo manifold looks like this: 

  

![](https://lh7-us.googleusercontent.com/pL6f7noftl7-xRibY7I9A-d8VJg247sUQ04EpQ8EhB4uey1rQsBsrT_pOEwDAXx8CBC8JS9_u3cHSsoE6JFyKTxY5EeAMHKFs0OOTLOH2l9IroKzq3f8wAPiY8gG6MidHXGG02Wuee6rqyPhyghjhww)

  

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## OK, those are lots of squiggly lines and pretty colors, but how do these translate into real-world numbers?  

  

Check out the charts below for the measurables!  We realize the text in the pictures is pretty small, so here's the legend:

  

Y-Axis (left) = Residual Ratio from 0.0001 up to 1.0

X-Axis = Time Step from 0 to 100

Y-Axis (Right) = Pressure (N/m2) from 1,000 up to 5,000/6,000

  

Pink = Eddy Viscosity

Blue \= Pressure

Green \= Velocity

Dashed Black = Inflow Pressure

  

The inflow pressure (black dashed line) is the main thing we’re looking at, but check out how much higher and smoother the velocity (green line) is on the new design (pay attention to the values on the right side; they’re different between the two charts).  FYI - The second chart is updated design Rev A (17% improvement), not the final Rev E (24% improvement), which is what we ended up choosing for our production turbo manifolds.

  

### Baseline (old design): 

  

![](https://lh7-us.googleusercontent.com/Hd9d5y8jBCEFMka7DjiX00dGyoFE1Z8kij7fzZ0lNlQFrP90Kjz5MBZaPOsxQ8FzIlhI7Q-fPKsu75bys66bEH-Nb7IoGzoFGPbRHFwSe5sio0ADeufY2KsCtbn8MrW7XyP5rZW-UYWerFTH66wIevs)  

  

### Updated design (this chart shows Rev A at a 17% improvement, but the final Rev E is a 24% improvement): 

  

![](https://lh7-us.googleusercontent.com/zGL93faPynWJW3g21QjZukf-FRHJvJ2cJUakPvl4xPBfHmJsRZMQKOk9GTfn7Yz4lgM-uxF1TYayCXs2xiPqGlGlADb50H0ry8q32HoNIX2ilo560V2kZ1QLYJqcQBXMcW3PkC7N6GmDq3uf4MNBwRc)

  

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## What about the 1.6L version? 

  

While we didn’t run CFD on the 1.6L turbo manifold - it would have been redundant since they’re so similar - we applied all of the same lessons we learned from the 1.8L.  And, 1.6L lovers, while we didn’t measure it, your improvement should be even better.  The turbo is slightly farther away from the engine than on a 1.8L, plus it’s a shorter engine fore-aft, so the runners on the 1.6L are even straighter than on a 1.8L, which should result in an even bigger improvement!  In fact, we've noticed that we're able to make roughly the same horsepower using the same turbo at about two psi less boost pressure than we did with the old 1.6L turbo manifold.

  

Another improvement gained by the redesign is a lower weight.  With the new design, the weight dropped dramatically - the 1.6L turbo manifold is 4.5 lbs lighter _(!!)_, and the 1.8L version is just over 2.5 lbs lighter.  Finally, just look at it - it simply looks like power! 

  

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## What's new about the FM turbine outlet?

  

While the turbo manifold got the bulk of the attention, we definitely didn’t ignore the turbine outlet.  After experimentation and many years of tuning turbo cars, as well as discussion with the CFD experts, we realized that we didn’t need a divider between the turbine flow and the wastegate flow.  Removing that divider allowed us to open up the outlet, improving flow and decreasing back pressure even more. 

  

Of course, it has the same great strength and compact fitment as before, but now it also weighs 1.4 lbs. less than the previous design, thanks to shedding the divider! 

  

![](https://lh7-us.googleusercontent.com/eSusNoeeE2SR7TUiTI8s4yopnutB5cRl0Jlvc8AgJmHoz3CUq4VWO5rkZIlLfIVDSQCeSK06OhfVVBAxeGw_XA7UWJQdPVIi8lmX20cjJaAZvdYBQqdy7S6Hw0FiiA50xL5_9DahEDv6XNJuhigFubc)