You Told Me What Engine I Should Swap Into My Miata - I Responded

In the introduction of our last article, I mentioned that the engine in my 99’ Miata is a ticking time bomb. I also implied that I was planning to do an engine swap, rather than replace or rebuild the factory motor. I then spammed the article around the internet, and before I knew it people on the Facebook group “Track Day, Bro!” were arguing over what engine should end up in my car. Flattered, I offered to write an article where I’d research and respond to each suggestion made. It wasn’t easy. You people suggested everything under the sun — you suggested engines that me, a self-labelled gear head, had never even heard of. Here’s the full list in all its glory:

  • Nissan SR20
  • Nissan KA24 (boosted)
  • Nissan RB20/RB26
  • Nissan Vg30et
  • Nissan VG33ET
  • Nissan VH45DE
  • GM Ecotec 2.0/2.2/2.4
  • GM LFX V6
  • GM Vortec 3000
  • GM LS1 (inc. Chevy 350/6.0L Vortec MAX V8)
  • GM 3800 Supercharged
  • Mazda 13B
  • Mazda 20B
  • Mazda FE3
  • Mazda 12b carbed
  • Mazda KLZE V6 (incl. Ford Probe V6)
  • Toyota 3SGTE
  • Toyota 4AGZE
  • Toyota 2JZ GTE
  • Toyota  7MGTE
  • Honda K20/24
  • Honda F20/F22 
  • Honda J-series
  • Ford 1.0L EcoBoost 3-cyl
  • Ford 3.5L EcoBoost V6
  • Ford 5.0 Coyote
  • Ford 302
  • Ford Triton v10
  • VW VR6 (+awd..?)
  • VW TDi motor
  • Subaru EJ20
  • Subaru EG33
  • Mitsubishi 4G63
  • Audi FSI 4.2 V8
  • BMW M20
  • Two stroke snowmobile engine
  • Geo Metro G10, 1.0L i3

Obviously a lot of these are ridiculous. The thought of a 1.0L i3 from a Geo Metro in my Miata made me ill. Very funny internet. Very funny. 

A Geo Metro powered Miata - yupp, it's been done.


There’s a problem with most of these swaps, aside from the fact that a few make less than 60 hp. More specifically, there’s a problem with me. I’m not a mechanical wizard who can fabricate engine mounts out of metal piping using little more than a tig welder and an angle grinder. I can swap suspension, alternators, control arms, i.e. fairly simple bolt-on tasks. Neither do I have the funds to pay someone to fabricate the necessary swap parts for me. That being said, if there isn't a swap kit readily available, I’m not doing it. Sorry internet.

That narrows it down to the following possible swaps: 

*I've included a link to each swap kit.

I mentioned before that this is a budget swap. The idea here isn’t to produce mammoth amounts of power — I just happen to have an oil-burning wretch of a motor in my car, so why not add bit of power. I can hear the communal sigh of thousands of enthusiasts hoping I’d announce that I’m building a Trition V10 powered Miata, but alas, I’m putting one more restriction on this swap to keep it truly cheap: it needs to retain the stock transmission. The stock Miata five-speed can only take around 250 whp reliably, so power needs to be kept to a moderate level. That leaves these available options:

  • Mazda 13b             
  • Honda K20/24
  • Honda J-Series
  • GM Ecotec 2.4l    

Mazda 13b  (N/A)           

Pros:
•    Inexpensive: $5000-6000 is a realistic figure for the entire swap.
•    Keeps the whole car Mazda.
•    Decent power.
•    Sky-high redline.
•    Low weight – retains factory weight distribution.
•    BRAP-BRAP-BRAP-BRAP (Killer exhaust note)

Cons:
•    Crappy fuel economy.
•    Frequent rebuilds – which I’m not qualified to do.
•    Little low end torque.

I completely understand why people love the rotary, though it’s the type of creature I prefer to appreciate from a distance. I road-race this car throughout the summer and it sees 30,000 kms of daily driving each year — similar to Sanjay’s RX-7. The difference however, is that Sanjay can rebuild a rotary in his sleep. I want to complete this swap and go on with normal maintenance as though it were a stock car. Also, getting 15 MPG from an N/A rotary making between 230-250 hp seems absurd. I’m of the belief that if you’re going to get V8 fuel economy, you should have V8 power along with it.


Honda K20/24

Pros:
•    Massive aftermarket support
•    Good N/A power
•    Light, Compact
•    Easy to source
•     “Vtec kicked in” jokes

Cons:
•    Little torque below 6,000 rpm
•    Expensive: around $8,000 all in, and motors alone are usually over $2,000.


K-series motors are wicked. I’ve seen dozens of people make 300 whp from N/A, street-friendly K24s, and I’ve driven modified K20 Civics. Very little compares to the 9,000 rpm scream of a modified k-motor in VTEC. The problem I have with K-series motors, is that when you’re not above 6,000 rpm (and you usually arn’t), they feel like anything else — slow. Their popularity in the Honda scene has also made them expensive. K20s regularly sell for well over $2,000. The K-Miata kit goes for around $4,000 USD. All in, you’re looking at well over $8,000 dollars Canadian. 


Honda J-Series

Source

Pros:
•    The most stock power on this list. (300+ whp)
•    Weight is comparable to stock.
•    Easy to source.
•     “Vtec kicked in” jokes.
•    Plenty of low-end torque

Cons:
•    Expensive: $8,000 all in is optimistic.
•    300 whp is a lot for the stock five-speed to handle.


Using Honda’s J-series V6 is an easy way to get 300 whp out of a Miata. “Super Fast Miatas” which makes and sells a J-series swap kit says that they can be mated to the stock transmission reliably. That being said, people who have road-raced Miatas for years have told me that the five-speed will begin to pull itself apart when subjected to more than 250 whp. The biggest problem however, is the cost. J-series V6s go for a pretty penny — usually over $2,000. The kit itself is another $3,250 USD. Once you start adding in an aftermarket ECU, a custom exhaust and a clutch, you’re looking at over $8,000 Canadian. That said, it’s tough to ignore the mammoth power to weight ratio of a 300 whp in 2300 lb car. 


GM Ecotec 2.4l    

 

Pros:
•    200 whp/200 wtq. 
•    Smooth, even torque curve.
•    Cheap — like really cheap. $4,000 all in. 
•    Within 5 lb of the stock BP motor.
•    Easy to source.


Cons:
•    “Ecotec just kicked in” isn’t quite the same.
•    No Honda street-cred.
•    Lower redline than the K20 – no crazy VTEC scream. 


This is a weird one. When you think of legendary four-cylinder engines, the 182 hp 2.4 L Ecotec motor that came in the 2012+ Chevrolet Equinox, along with a whole bunch of other boring GM vehicles, probably doesn’t come to mind. This option wouldn’t have crossed my mind if MT Motorsports hadn’t produced and advertised a swap kit for this forgettable engine that promises 200 whp, 200 wtq, a torque curve that’s smooth as butter, which can be finished for $4,000 all-in. The enormous power bump comes from a 91 octane tune. Because these motors are somewhat unknown and plentiful, they’re really cheap – $500 is average for a low mileage example.


By now you can imagine which direction I’m leaning. But before I put my money where my mouth is, I decided to take a drive down to MT Motorsports to drive their Ecotec powered NB Miata, and  find out if this strange engine swap is all it’s cracked up to be. All that in our next article.