In my experience it's a combination package. For the bolt on's like inlet manifold, TB, exhaust headers and exhaust system use what a good/excellent NA build would choose.

Excellent N/A Build Bolt-Ons:

• Flattop / Skunk2
• OEM / Skunk2 / 68mm Chinese
• RacingBeat 4-2-1
• High-Flow Catalytic Converter
• 2.5“ / 3” Exhaust

The Rotrex will provide say 15psi on the inlet manifold. The bigger the exhaust system say going from 2.5“ to 3”, the less boost you will get as more blow through. But power most likely will be the same or more, as will fuel flow requirement due to the blow through.

Exhaust Backpressure

• Stock Exhaust: MAP = Backpressure (13 PSI) @ 7200 rpm (https://www.mazdaspeedy.com/content/images/2019/05/EBP.JPG)
• Stock Muffler: 5 PSI Backpressure
• Race Cat: 3 PSI Backpressure (https://www.mazdaspeedy.com/exhaust-backpressure-part-2/)
• Free Flow Catless: 4 PSI Backpressure (https://forum.miata.net/vb/showthread.php?t=553290)
• Metal Cat, 2,5“ Exhaust, Resonator and Magnaflow Muffler: 5-5.5 PSI @ 10 PSI MAP @ Redline, (https://www.miataturbo.net/engine-performance-56/i-measured-exhaust-backpressure-59103/#post749282)

As it's important to trap the fuel/air on the valve overlap, higher lift and longer duration NA cams tend to loose power due to blow through. Specific fuel consumption goes crazy as well. On the K22 going from stock to Stage2 NA cams was +50% injector flow. Power was almost the same.

As you widen the lobe centre between the inlet and exhaust the engine becomes less prone to knock. This is a big factor if you have poor fuel and or a relatively high dynamic compression ratio on a boosted car. So wider lobe centers can make more power and reduce overlap.

My approach to the cam design was to try stock, other supercharger cams, then stage 2, model the results with software and then design my own. I ended up with wider lobe centers with less overlap than stock but lift is similar to stage 2 or stage 3 camshaft depending on the vendor. Also plenty of duration at 0.500”.

This is not easy to do while keeping acceleration, jerk and hertizan stress close to OEM.

So I would try the mildest inlet cam you can find, hopefully with more lift than stock. And a stage 2 exhaust cam as a starting point. Fit a venier exhaust cam gear to advance it's centre line. Position based on dyno tuning but 6 degs advanced is a starting point depending on the duration.

.427 (10.8mm) cam lift intake, 272° .410 (10.4mm) cam lift ex, 266°

Clearances are bigger than OEM so actual lift is less of course. That's about the most duration I would run in an engine expected to idle. A VVT head might tolerate another 5-10° since you can dial out some overlap at idle and IVC doesn't really affect idle vacuum.

So these are really midrange cams. Even with IRTB's I would expect peak power to occur around 7700 and roll off to about 8400. Peak torque will still be in the 6100rpm range I think.

- emilio700 (https://www.miataturbo.net/engine-performance-56/2-0l-bp4w-182whp-63455/page5/#post835745)