This is by far one of the biggest worries and frequently asked questions we get about our 2016 Miata Turbo Kit. Most people point out the engine compression ratio of 13.1 is too high for forced induction, and that a lot of the cup guys are breaking their ND transmissions with close to oem power levels.
Is the engine compression ratio too high in the ND miata? Isn’t 9.0:1 or lower more ideal? Low compression used to be more ideal for a safety net when turbochargers were first becoming popular on carburetors; below 7.0:1 was not uncommon. A lot of people were not using inter-coolers, and simply locking the timing advance on the distributors. While we are not experts in turbocharged carb setups, we do have first hand in experience, and we can tell you it takes some serious experience, and time to tune one properly. Its not surprising a huge safety net was needed. Engine compression ratios raised with better fuel quality, auxiliary injection and more notably fuel injection. Fast forward to the present day and high compression turbo engines are becoming a lot more popular. The S2000 ( 11.7:1 stock), and BRZ/FRS ( 12.5:1 stock) are extremely popular turbo platforms. The Skyactive engine found in the 2016 Miata features an advanced piston dome shape that helps control detonation. Direct injection produces a much cooler intake temp charge compared to port injection( no port wall wetting), and has the ability to be phased more accurately. High intake temperatures are one of the biggest reasons engines detonate in the first place. Combine all of this with an extremely advanced closed loop knock system and one will see the need for lower compression ratios with forced induction are a thing of the past.
Engine aside, what about the drive-train holding up to the increased power of a turbo system? Well we do not have all the answers here, but we have done close to 3000 very hard miles on our turbocharged ND Miata. We are making 70 more rwhp, and 100 more rwtq than stock. We have also done 5 track events, including 3 autoX, 1 drag, and 1 roadcourse. You can view those here on our youtube page; TurboSource Track Videos. Only time will tell,but rest assured we do intend to find out. Sometime in the coming next two weeks we intend to turn the boost up to find the first mechanical weakness of the car, be that 10, 15 or 20 PSI. Stay tuned for the next update!