Originally Posted by PorkChop
Some pointers about donor choice, or things to look out for if you're buying parts piecemeal rather than a complete donor.
All the 1600 and 1800 parts are interchangable to an extent. For example, you can run a 1600 engine and gearbox with a 1800 diff. You would need a 1800 prop and drive shafts to suit the diff. A 1600 engine will fit a 1800 gearbox.
Apparently (I don't know if this is true or not) but the 1600 gearboxes and diffs are slightly weaker than their 1800 counterparts.
A common upgrade for the 1600 engine (especially if tuned) is to fit the 1800 flywheel and clutch.
You can tell the 1600 and 1800 apart by looking at the cam cover - the 'Mazda 16V DOHC' lettering is raised on a 1800, sunk on a 1600. The 1800 has 'BP' cast into the block on the exhaust side.
The 1800 comes with bigger brakes as standard all round. Mark 2 Sport brakes are bigger still.
Early driveshafts are bolt on (and the PCD is different between the 1600 and 1800). Later driveshafts are push on (and I believe are still different between the 1600 and 1800).
There were several wiring revisions over the course of the mark 1's life.
Early 1600s ('short nose') engines had crank problems. Later long nose engines are fine. They can be identified by counting the number of slots on the crank pully. The short nose has 4 slots, the long nose 8.
Any imported (Eunos) 1600 engine will be 115bhp, as are UK engines of the same era. The JDM 1600 was discontinued when the 1800 was introduced. The UK 1600 was then detuned to 88/90bhp at this time, so any later UK spec 1600 would be the 90bhp version.
The OEM alloys are very light for an OEM wheel. You would need to spend a significant amount of money to get lighter aftermarket ones.
A mark 3 MX5 gearbox will fit the Ford Duratec apparently
The mark 2 6 speed box is rumoured to be stronger than the mark 1 5 speed.
Little can be swapped between 1600 and 1800 engines but they do both fit in the same 'hole' and fit on the same gearbox.
1600 diff up to 94 is 6" crown wheel from 94 all diffs 7" crown wheel and essentially the same as RX7.
7" naturally stronger than 6" but both are stout. 6" are open or the unpopular VLSD, 7" available as open or with Torsen type 1 or 2.
Three different types of driveshaft depending on the diff you have so get the driveshafts at the same time to go with the diff.
MK2 gearboxes are 'better' than mk1 in that the mk1 is intentionally noisy but this proved unpopular and the leaky remote change was redesigned but both are equally stong as they came from the B1600 pick up.
Clutches - If running a tuned 1600 N/A engine then avoid the heavy 1800 flywheel better to use a H/D 1600 clutch. I'm using a 1600 flywheel and clutch on my nearly stock 1800 with no problems.
If turbo'ed then use the 1800 flywheel and MX6 clutch unless running mental amounts of power
5 speed boxes have better ratios that the 6 speed and in something like the haynes roadster first in the 6 speed would be pointless. Just extra weight to carry around and as its bigger, more of a squeeze on footwell space.
Brakes - Mk1 1800's have bigger front brakes, Mk2 1600 and 1800 had the MK1 1800 brakes and bigger rears, MK2.5 had bigger fronts again and then there were bigger rears for some special editions.
Wheels MK1 all 14" MK2 15" MK2.5 16" mk3 17"
Mk3 MX5 does indeed use the duratec engine as it was part developed by Ford and Mazda. (Well Ford does own part of Mazda)
So a Mondeo engine can be used but a mazda flywheel clutch and starter will be needed. I have a MK3 6speed if anyone wants to make me an offer?
MK1/2 parts Hardly anything interchanges with the MK3's. The MK3's all different, being based around the RX8.