Miata: NB block in NA car?

So I am debating about picking up a '97 Miata, there is a hole in block, and a bent exhaust valve. I also found a C.L. add listing a '99 motor & trans. I found out that the '99 has better flowing head, uses different intake manifold, fuel rail, and cam sensors. The pistons are also "crowned" for an extra 0.5 compression ratio.

So are the transmissions the same?
Can I get '97 head repaired and put it on the '99 block w/o any extra issues?
Will another Miata guru notice the block is from a different year? This motor has been sitting for 2yrs in the guys garage, if it spins over is there anything to worry about?

TIA!

Easy. The transmissions aren't identical, but interchangeable. Better 3rd gear synchros with the NB one, although by this point in their lifespan the difference will probably be more closely related to the life the transmission has led. Get the NB starter if you can, it's lighter.

You can put the NA head on the NB block, no problem - although I wouldn't.

It's tough to spot different blocks. I'm not sure I could tell the difference offhand.

Other minor differences -- you'll want to keep the NA alternator, because the NB one requires computer control. The NB head is better, but you'll want a simple RPM-based switch to flip the solenoid for the 99 VICS intake at the right point. I'm not sure if you can use the 97 fuel rail on the 99 intake -- you might need to use the 99 rail and modify it to use on a return-based fuel system. There are lots of writeups on this kind of thing on miata.net.

The 99 fuel rail modification consists of: mount the FPR from the NA on the end of the rail.

Keith Tanner wrote: The 99 fuel rail modification consists of: mount the FPR from the NA on the end of the rail.

I think the devil is in the detail wrt. the fuel hoses & connectors. Here is the best explanation I've seen on it: Update to '99 Miata Head on '94 Engine - Fuel Rail Issues. Summary is: get SAE 30R9 fuel hose (I could only find this at NAPA) and the special connector (DORMAN 800-081) to the fuel rail.

The only other thing I found is the EGR ... the '99 EGR valve [BP4W-20-300A-9U] has a different electrical connector than the '94 EGR valve [B6BF-20-300-9U]. I re-used the '94 EGR valve on the '99 intake so it would plug into the car's existing harness.

-- Pete

I have a 99 fuel rail with 94-97 FPR in my car. No issues with standard fuel lines clamped onto the inlet and outlet with the stock hose clamps. I have put ~10k miles on it without a leak.

On-topic, but a bit a a derail. I have a friend who just got a 97 miata with a 99 head on it.

It is megasquirted and turboed, he needs to get it through emissions, which if I am not mistaken, around here means OBD2 plug-in and has been asking my advice.

I was thinking the best route might be to zero the boost and put a stock computer on it for emissions day, but is that possible with the 99 head? (97 OR 99 computer?)

I installed 1.8 in a early 1.6 car years ago. The only problem was back dating the intake and FI system; sounds like this proposed swap is very similar.

Fuel lines are easy. You can either just slip regular lines over and clamp them on, or you get a "fuel line repair kit" from your local auto parts store that consists of the clip-on connector with a hose barb on the end. Not difficult at all. Almost every "high pressure fuel line" is the clamp-on style.

Apexcarver wrote: On-topic, but a bit a a derail. I have a friend who just got a 97 miata with a 99 head on it. It is megasquirted and turboed, he needs to get it through emissions, which if I am not mistaken, around here means OBD2 plug-in and has been asking my advice. I was thinking the best route might be to zero the boost and put a stock computer on it for emissions day, but is that possible with the 99 head? (97 OR 99 computer?)

If he knew he needed to pass OBDII tests he should have bought a parallel install megasquirt instead of an PNP. He'll need to put in the stock injectors, wire the wastegate open. Trouble will be getting all the readyness monitors to set while driving in a way to not hurt the car like that. I'd throw the stock header back in to make it easier. I'm assuming that because he's using an MSPNP that he's running a stock CAS on the back of the head and the 97 crank sensor rather than using the better 99 cam sensor.

Car was just purchased with the modifications in place.

Will send you advice on to him.

Leafy wrote: If he knew he needed to pass OBDII tests he should have bought a parallel install megasquirt instead of an PNP. He'll need to put in the stock injectors, wire the wastegate open. Trouble will be getting all the readyness monitors to set while driving in a way to not hurt the car like that.

I can't say about the 97 computer, but the 99 one is happy to set all of the readiness monitors with a single drive from cold, never going over about 30% throttle or 3500 RPM.