Part 3 of the Miata 2.5L Swap - The Finished Product

March 13, 2024

From August 14, 2023 to February 28, 2024, my 2006 Mazda Miata went down due to a blown clutch and underwent an full rebuild from the ground-up including a new powertrain, suspension, and TONS of supporting modifications (for the full list of parts, see my prior post here). Without further ado, here is my review of my cammed 2.5L Miata...

Powertrain

The first question everyone asks (and was the first one I asked too) is "what does a 2.5L Miata feel like?" I think the best way to think about the car is OEM+ (Original Equipment Manufacturer). The power band feels linear, but has more power in every area. 

Here are a couple of dyno graphs to help better visualize this:

This is a stock 2014 Mazda Miata with a Versa-Tune Stage 1 Tune (same as what I was running prior to the engine swap. The power output was respectable at:

Quick recap of the numbers above:

• 147 horsepower @ 7,000 RPM's
• 129 foot/pounds (ft/lbs) of torque @ 5,100 RPM's

Now here is a 2.5L swap dyno with the same camshaft that I am running in red:

And that same quick recap:

• 203 horsepower @ 7,100 RPM's
• 177 ft/lbs of torque @ 5,500 RPM's

Those raw numbers may still seem relatively small and they are, but those are HUGE gains in terms of percentage. In terms of both horsepower and torque, it's a nearly 30% gain respectively! The other callout is the usability of the power, especially the torque available at all parts of the powerband.

Now of course I had to go out and do some 0-60 runs. I will note that I was trying to avoid hard launches as the rear differential does use clutch packs and will become the weak link of the vehicle, especially with hard launches. That said, my best time was ~6.3 seconds using a GPS app on my phone. Please note that this car is not made for fast 0-60 times; if it was it wouldn't require 3rd gear to hit it.

Suspension

Once the Miata was back from Fab9 (shop that performed the shop), it was evident that my suspension was done. When even moderately accelerating (think 40-60% throttle applied), I was experiencing a borderline unsafe wheelie-effect where the weight in the vehicle was transitioning to the rear thereby picking up the nose of the vehicle. Then once you let off throttle, all of that weight transitioned back to the front causing scary handling characteristics. This is what you might refer to as too much power for a given setup. It was time for a change...

My thought processing was similar to that on the powertrain upgrades where no dollar was spared and I wanted to ensure that I was running the correct setup. After a month of research and squeezing a few pennies together, I purchased a set of Ohlin's. This setup definitely cost more than what I was really wanting to spend, but I felt it was the correct move to do things right.

After installing, I took my Miata on a shakedown run. Prior to this shakedown I did not adjust dampers or the adjustable shock. My immediate thoughts were that this was much better!

The following day I took the Miata to Butler for an alignment and (since they are a specialty automotive shop) requested that they dial the suspension (dampers and springs) to an "ideal canyon carver" or borderline street racecar. It took a few hours and tightening some things that I had left loose, but they finished it...

The best thing I can compare it to is a new vehicle. Here are the main things I've noticed since switching from the Club Bilstein's:

• No more body-roll
• If you ever drive a Miata (regardless of generation) in stock form, you'll notice that on twisty roads it has compliant suspension but when pushed to the limit it can move a LOT
• The Ohlin's resolve this by lowering the vehicle and making it stiffer, thereby removing the body-roll that existed before providing far more confidence
• No more terrifying "wheelie" mode
• The power of the 2.5L is being put down better than the Bilstein's with the OEM 2.0L
• Direct handling
• If you steer one way, the car immediately does it with no hesitation in steering and truly the car does feel like its on rails with regards to handling 

Final Thoughts

While the above items are awesome, the Miata does feel more like a new vehicle that I am actively trying to find the limit when pushing it. Between the new-found power plant, overhauled suspension, and new tires, I find myself pushing and pushing, but have yet to feel like I'm not in control.

At the end end of the day, was the $10,115 that was spent on my NC for all of the work worth it? Unquestionably yes. My car is the perfect combination of power and handling for what I like to do ("Canyon Carving"), while still not being terrifying. I wouldn't change anything. With that said, there is absolutely nothing wrong with a bone stock NC Miata and its a super capable vehicle, but I'm happy and excited to have limits beyond what it could do from the factory!