The first thing I wanted to know when the NC was released was how it compared to the previous generations. Which parts was carried over from the NA/NB. What is new. What other car shares the same platform, why is it better etc.

I have not found a thorough comparison other than Mazda own words which is very vague press material and some obvious stuff like dimensions and new engine etc. from the Miata wiki:
I'm sure there is a lot of info out there spread across several forums but thats a lot of searching and the potential of fff'ism.
This will by no means be a complete summary. Only some observations I did while spending some time under the car while changing fluids.

First the obvious. It has grown in size since 1989

Wiki says:

NA: 3,950 mm  x 1,670 mm x 1,220 mm   940 kg
NB: 3,940 mm  x 1,680 mm x 1,230 mm 1,065 kg
NC: 4,000 mm  x 1,720 mm x 1,240 mm 1,095 kg

I'm impressed that Mazda was able to keep it at 1100 kg when redoing the roadster in 2006 having to conform to all kind of safety and comfort requirements.  Both the Porche Boxter and the Merc SLK are over 1400 kg. ( .. and some more powers..).

The Interior is all new. All plastic but rugged and doesn't feel cheap. They have incorporated cupholders in the doors without making it cramped like the NB.  There are stowage boxes behind the seats for the non PRHT model.  Seats are phenomenal compared to  NA/NB but also weigh more. Steering can be adjusted in height.
The door sills are higher and hopefully gives increased stiffness.
There is a bulge on the right side of the transmission tunnel to make room for the pre-CAT on the manifold ( LHD, no problemo ).

Spare wheel in the trunk is replaced by an air compressor and foam.  You need to replace the foam every 2 years....(won't happen..)  Car jack and gear are stowed on the sides instead of under the trunk floor.  Battery is now located in the front.

The front of the car (2006-2008) is inspired by the NA . Every model has holes for foglight but they are plugged on the base models.  Very convenient for CAI, brake ducts etc. 

Only half of the radiator intake is actually open. The upper part is designated for the numberplate which I guess is OK since they didn't take that into cosideration on the NA/NB.

 A considerable amount of cooling air is coming in from under the opening as seen on the photo below.

The radiator is a crossflow type which is supposed to be a superior design compared to having the cooling channels standing according to the internets.  The PS cooler is considerable larger than on the NA/NB. Maybe the smaller PS pump needs cooler fluid.  There are some interesting ducts on each side of the rad which I first thougt was brake cooling.  It is not but I'm not able to see where it leads due to cramped space.

 The undertray looks to consist of several parts instead of one the previous one piece design. They have added flaps on each sides that covers the suspension area. I guess this is to reduce drag across a turbulent area or just a simple form of airdam. Most new cars have them and they are handy on lowered cars giving an early warning when crawling over bumps etc.

 The underside has a couple of stamped braces including a x-brace. I don't have a proper pic of the whole undercarriage but they are barely visible on the pic above.  The subframe and middle brace has tabs that looks to be made for additional panels. Maybe later models have them or they are missing from my car...

  The front suspension are new with cast aluminium upper and lower A-arms. Coilovers has the same design but uses a progressive spring and 3 bolts on the upper mount.
Sway bar has a proper non flexing mount.  Stock front bar is 21mm on this particular model. Rear is 10 mm.

Front hubs have the hall sensor for ABS/DCS integrated in the center of hub.

Brakes are now 290 x 22mm (11.4")  front. Not sure about rear. Still using single pot cast caliper.
NBFL sport brakes are 11.0" in comparison. Minimum 16" rims.
Hubs are now 5 x 114,3 which means a huge selection of wheels.

Oilfilter is now located under the engine facing down.  EU-models have a water to oil cooler stock. Even my 1.8.  I suspect this is more of a oil warmer than cooler, but I could be wrong.  Goodwin sells this as a performance item for the US version which comes without one. I wonder if that sensor is for pressure (gauge) or temp.

Both the manifold and the midpipe has a CAT with an O2 senser each. At leas one of the is a WBO2 (0-5v) type. Both are generously heat shielded.
Midpipe OD is 59mm or 2.3".

Transmission looks familiar. It might be the standard 5-speed from NA/NB but with a different bell housing and shifter section.  Note the 10mm heat shielding on the tunnel.  Hopefully this cures intense heat radiating into the cabin when on track.

Differential is new.  Axles looks like the MSM ones which is rumored to be from the RX8.  OD are 27mm towards the knuckles and 36mm on the middle section.

Rear suspension is of multilink type doing all kinds of crazy stuff when compressed. There are 5 arms on each side. At least 3 of them mounted to the hub with a ball joint/track rod.
Camber/toe adjustment is with camber bolts but with bigger diameter than previous generations (19mm vs. 17mm).  Thats nice since I have had mine slip twice on previous generations.

Engine is the all new (at least in 2006) MZR engine which is also used by Ford under the name Duratec.  This is the welfare class 1.8 liter version. Gasoline version of the MZR exists in 1.8, 2.0, 2.3 and 2.5.  The latest in the US 2009+ Mazda6.
They have VVT, electronic TB. Dual feed fuel rail with oldschool non direct injection.
Exhaust are now routed on the right side of the trans. Engine is located behind the front "axle" like the S2000 which makes it a MR :) . This in combination with the rad tilted forward has made it possible to put all the boring stuff like air box, battery, coolant tank, fuses etc in front of the engine. It looks like most of the cooling air flow escapes trough the trans tunnel.
Higher spec models have a nice cowl triangulated shock tower brace.

There is still room behind the right shock tower for fun stuff (like relocating the battery for a rotrex etc..).  Exhaust manifold has two heat shields  One mounted to the frame rail to protect the abs and brake lines.  EGR is now integrated in the block with a "fifth" exhaust port.

Airbox looks non restrictive and sucks air from the front of the car. TB is 55mm electronic stepper type.  I really like the use of quick disconnect fittings instead of old school worm clamps.

Cold side of engine is all hoses.  IM is molded plastic and is rumored not to like boost. PS pump is mounted in front of IM and are really small.  The clutch now shares fluid with the brake reservoir.


The NC shares very few parts with the original NA and NB but the principal design is much the same; FR layout Roadster, PPF, 4-cyl N/A.
The main differences are multilink rear suspension and a new generation engine. ( PRHT for posers).
The NC tuning scene is very different than the BP based NA/NB. It could be due to very little space for a turbo, tricky ECU with electronic TB,  weak rods/crank on pre 2009 models and many owners might feel the car is to new for serious hot rodding.  Sniper and ECU Tek  ECU rempap are popular but gives modest results.  The Cosworth designed MP62 supercharger kit is very well engineered but expensive for a sub 200whp 2.0 litre engine.

All things considered.  I like it.  A lot!