Nitroracer UltraDork
8/5/18 7:38 p.m.

I have a 99' Miata worth looking at this week and it may or may not have a 'blown' engine.  The description from the seller says its blown, after running on the highway over heating and shutting off.  Now it runs again?  I'm treating it as wounded, but I'm not sure how badly yet until I can diagnose it.  What are my options for replacement?  Is any 94-00 1.8L applicable?  Can I mix and match 99' parts on an older engine?  Do I hold out and look for a later 01+ engine with variable valve timing trickery?  How much cost and complexity does it add to upgrade, and is it worth the minimal bump in power?  Sorry, for the word vomit.  Just looking for what my options are.

BoxheadTim MegaDork
8/5/18 7:44 p.m.

99 and 00 are using an engine that's unique to those years. IIRC the block might be the same as the 94-on 1.8, but the head, intake and potentially the header are different. Plus, the compression has had a bit of a bump as well. So I'm guessing it really depends on what got cooked.

01+ will require engine management that can drive the VVT. A properly mapped VVT engine should have a reasonable increase in power over a 99/00, but you probably need a full standalone at that point. A VVT motor might actually be easier to find, in my local FB Miata parts groups, it looks like people want the 99/00 engines (specifially the heads) as it's an easier retrofit to an NA if you don't like standalones and wiring.

rodknock New Reader
8/6/18 6:51 a.m.

The 99-00 motors command a decent premium over the other 1.8s for the reasons listed above. From what I remember the wiring for a VVT swap into a 99-00 was more involved than it should be. 

If he didn't completely Chernobyl the head when it overheated you might be able to get away with fixing whatever caused it to overheat and slapping in a new headgasket. 

If the head is still good and the block is toast you can use an early 1.8 block with some VVT pistons to get a bump in compression for not a lot of cash. 

spacecadet New Reader
8/6/18 10:16 a.m.

Go read through the thread where Mazdaduece fixed the motor in my 99 earlier this year. 

The 01-05 blocks work and bump the compression up slightly. 

Keith Tanner from Flying Miata kicks in advice. 

Rodan HalfDork
8/6/18 11:03 a.m.

Swapping an '01-up (NB2) engine in a '99-00 (NB1) is about as simple as it gets.

The only real physical differences are the intake and exhaust manifolds, and the coils.  Intake is considered superior on the NB1, so swap that over from the dead engine.  Exhaust is superior on the NB2.  You will need the EGR tube from the NB2, as they are different on the exhaust side, identical on the intake side.  Midpipe fitment is identical, so the exhaust is a bolt-in.

NB1 coils have a reputation for failure, so try to get the coils/ harness with the NB2 engine.  It's a simple job to wire them up, and they'll work fine with the NB1 ECU.  You can get the connectors new if you can't get the harness.  If you're stuck with the NB1 coils, they'll work, but the holes in the cam cover for the plug wires on the NB2 are smaller, so you will have to open them up, or shave the NB1 wires to fit.

Also swap the engine harness, injectors and fuel rail from the NB1.  You'll also need to extend the cam position sensor wiring.

Otherwise, it's a mechanical bolt-in.

The VVT can be left disabled, and the engine will run fine.  It will feel a little flat in the midrange, though it's probably making just as much as an NB1 engine, just pulls harder on top.  You can pick up a VVT tuner or standalone ECU down the road and reap the benefits later.  The VVT really wakes up the midrange, so it's worth it.   

Otherwise, the NB1 ECU will run the NB2 engine just fine.

NB2 engines are cheaper and more plentiful, and have more potential, so it's really a no-brainer.  I've done it twice, three times if you count putting an NB2 engine in my NA (which was a whole different story!).

Lot's of info on NB2 into NB1 on this page of my build thread:  Rodan's Miata thread

There's a link to info on the coil wiring in one of the posts on that page.

Here's a link to the coil pigtails:  NB2 coil pigtails


Rodan HalfDork
8/6/18 11:07 a.m.

Forgot to address the condition of the 'blown' engine...

If it overheated to the point it shut off, it's probably going need at the very least, a head gasket.  It's likely that the head is warped, and there's a good chance it's toast, especially if coolant got into the oil.

I wouldn't hesitate to buy it if the car is solid otherwise.  NB2 engines are plentiful and cheap. wink

codrus UltraDork
8/6/18 11:46 a.m.

Keep in mind that, while the BP4W was only sold in the 99 and 2000 model years, those are far and away the largest model years in terms of production numbers.  Can't find the numbers right now but I seem to recall that there's only something like 20-30% more NB2s than NB1s, despite 5 vs 2 model years of production, so BP4Ws are not rare.


If you swap an NB2 engine into an NB1, you'll want something to control the variable valve timing.  There's a standalone controller available, but it is an additional complexity.


Jaynen UltraDork
8/6/18 12:18 p.m.

I will say that I overheated mine and did not blow the headgasket but did blow the radiator so the headgasket is pretty tough on these

Nitroracer UltraDork
8/7/18 9:25 p.m.

Thanks for the information guys.  I missed out on this deal right as I was calling to confirm a time to check out the car.  Better luck next time!

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