I read a thread from 2012 on Miata.net that summed up the ideal build pretty well:
Savington said:
01-05 VVT motor
EUDM Squaretop intake manifold + 64mm Skunk2 TB
Custom intake
RB 4-1 header
High-flow catback exhaust
Standalone ECU of your choice (we prefer AEM)
Bolt the bits onto the motor, put the motor in the car, set up the ECU, and have a professional tune it. On a dynojet, this setup will be worth 145-150whp.
Headwork is completely unnecessary - you can meet your goals with a 100% OEM longblock.
The K20/K24 swap would be pretty sweet if it didn't end up costing a ridiculous amount. Looks like they're tryiing to use as many OE Honda parts as possible which is nice. Also there's talk of a tubular subframe to avoid moving the rack.
K20 swap is super cool, but I'd like a cheaper Honda engine option, and for all that money they are spending a LSx swap could be had.
$1000 kit to swap in a $250 motor, awesome.
$2000 kit to swap in a $2000 motor, not so awesome.
PHeller wrote:
K20 swap is super cool, but I'd like a cheaper Honda engine option, and for all that money they are spending a LSx swap could be had.
$1000 kit to swap in a $250 motor, awesome.
$2000 kit to swap in a $2000 motor, not so awesome.
Unless you are doing a ton of your own fabrication, a well done LSx swap in a Miata is going to be more like $10k.
Thing is, the amount of effort or money it takes to do a swap kit well isn't tied to the purchase price of the motor.
As for cams, I have a Web Camshaft 505 on my 1.6. It's a happy little engine with 148 rwhp. I haven't tried their cams for the 1.8. Integral did do some good stuff, although they had more luck with the solid lifter 1.8s than the hydraulic ones.
GameboyRMH wrote:
alex wrote:
Spending metric dollars on weird parts that don't net a whole lot of power gain isn't a plus, however.
Well that's too bad because you just described the process of getting big power gains out of a N/A motor 
Seriously you go N/A if you want rock solid reliability and modest power gains. If you want serious power without spending even more serious dollars...you need boost.
There is another potential metric you did not factor in. If it is a daily driver that will see the occasional 3-8s WOT blast up through the gears and maybe a few autocrosses a year, a turbo Miata can be built pretty cheap. Total DIY with FPR, ebay parts and used turbo? $900. Or but a nice FM, BEGI kit for $3000-$5000.
Where things come unraveled is for the expert driver that plans to do 20 minute HPDE sessions, TT or w2w in 100° heat. That driver needs to spend $10K if he is just swiping credit cards, or a few hundred hours if they are fabbing everything.
- A Miata newb buys a craigslist Miata for $2000
- Reads forum post about awesome $900 DIY trubo!
- Proceeds to blow up engine on 3rd lap at local track
- Sells Miata
If I had a buck for everytime I have seen this happen, I'd buy everyone reading this a nice lunch. We race N/A cars for one reason: They cost way less to build and maintain that a turbo car. This is not conjecture, but direct personal experience. There is no free lunch when it comes to power adders if you are going to hammer on the car once it's built.
Rock solid reliability on track, for an expert driver is far cheaper N/A than turbo.
To the OP
Alex, what are your plans for this build?
-daily driver, weekend only toy or trailered race car?
-drift, drag, commuting, canyon runs, TT, HPDE, w2w?
-lbs/hp target for car?
-fuel octane?
-expert ECU tuner available for it?
Good points Emilio, I went NA on my Corolla for the same reason. I could have slapped a turbo on it for the same money and had more power and more potential but I want that rock-solid lap-after-lap reliability and an engine that won't blow up no matter how much I wail on it. I know I'll hit a nasty price cliff if I want to mod it past a certain level, but my plan is to beat the cheap turbo crowd with consistency 
Unlike Keith and Emilio, I only know Spec Miata engine builds. So let me add some input from that perspective.
A nice 94-97 1.8 motor built with stock sized pistons and SM legal headwork can make ~120 rwhp +/- 5hp. This is on the stock intake, stock header, stock cams, stock ECU, SM restrictor plate and adjustable Fuel Pressure to lean out mixture and tuned AFM. If you go beyond SM legal headwork, another ~5 HP can be had. Increase bore and you have a couple extra HP and torque.
A nice 99-00 1.8 motor built with stock sized pistons and SM legal headwork can make ~125 rwhp. Again with stock intake, stock cams, stock header, stock ECU, SM restrictor plate and adjustable Fuel Pressure to tune/ lean out the mixture a bit. Adding an open intake and adjusting fuel pressure to tune AFR will put you at ~135 rwhp.
This is all on CA 91 octane pump gas.
SM legal heads run from $900-1,500 depending on builder.
