Miata Engine Mix and Match

I've got a 1999 Miata that I autocross (STR, no longer competitive, so changing to XSB) and take to track days.  It recently threw a rod and punched holes, so the bottom end is not rebuildable.   Used engines for 99-00 Miatas are a bit hard to find.  I've got a 97 core I could rebuild.   Please help me understand the options.  For now, I want to stick with a basically stock engine.

1. If I rebuild the 97, I'd need to use the 99 head due to the cam sensor change.  My understanding is that the 97 had a lower CR than the 99, but I don't know if that's because of the pistons or the combustion chamber in the head.  I'm assuming it's the pistons, but would appreciate verification.  If I rebuild the 97 with 99 pistons and use the 99 head, that should give me basically the same engine again, right?  The last short block I rebuilt cost about $1100, not too bad.
2. I've seen some used VVT engines for $750-900.  If I put the 99 head on a VVT short block, I think I get basically the same engine but end up with a lower CR again.  But it's a pretty cheap and easy swap, plus I could upgrade to the VVT later if I choose.  Thoughts?
3. I may do something more radical in the future--boost or engine swap--but want to keep this fairly cheap with fast turnaround to get the most out of the car through the driving season.  Between my sons and me, we have 4 Miatas that can use this engine, so we'd use this engine as a spare if I do something later.
4. Any other recipes I'm missing?

Thanks!

One option is to use the whole VVT engine. Disconnect the VVT solenoid and the cam will lock itself out, or use a VVTuner piggyback or full standalone to control the cam.

The 1999-00 engine was the lowest production variant, had the highest mortality due to a thrust bearing problem and is most sought-after because it gets you the better NB head without the scary concept of VVT. This means they are the most expensive.

1. You can put the 99 head on the 97 block. You want to, it's a better flowing head. I don't recall combustion chamber volume, I think most of the compression difference is in the pistons.  This is a pretty popular thing to do, lots of NA Miatas have NB heads these days.

2. 99 head on a VVT bottom end will give you a compression bump over the current engine.

I'm with Matt. Put in a whole VVT engine and use VVTuner to run the cam. You'll get a wider torque curve. I don't like the locked out VVT myself, you're leaving a bunch of potential on the table.

Easy button is the the VVT engine.  I have an NA track car with a VVT engine running on MS3 (VVT working and tuned), and a '99 NB street car with a VVT engine running on the stock computer (VVT not working - yet).

On the street the difference is very noticeable.  The VVT adds a good amount of midrange torque.  For autocross, I don't think you'd notice the lack of  it so much, if you're not dropping under ~4k rpm on your course.  The good news is you can bolt the engine in and run it, and add the VVT tuner later so you don't have to eat it all at once.  And VVT engines are the cheapest NA/NB engines available right now.

Use your '99 intake, and the VVT exhaust manifold if you can get one.  Better yet, if you search around on MT.net, there's a UK dismantler that will ship engines to the US, and they'll come with the Euro 'flat top' intake manifold, which is good for a slight power bump.  Prices are comparable to buying an engine here, cheaper if you have to have one shipped within the US.

I'd pull your cams on the 99 head to make sure it's ok. I bet there's a bunch of scoring from metal debris from the bottom end failure. Agree that VVT swap is the way to go regardless. 

VVT is definitely the way to go.  All engines that get upgraded to VVT make more power over a broader range.  If the engine is cheap too, then you can figure out the wiring and ECU to make it run.  I guarantee if I go to the trouble to swap a turbo engine into my Subaru I'm going with a more modern AVCS one (Subaru VVT).  I would have to rewire the entire dash and engine compartment, but this the route I will go if I ever decide I need to be in mod class rallycross.  I'm running stock this year and will likely do prepared next season.

https://www.iwireservices.com/post/2017/12/08/what-is-subaru-avcs-bran-avcs-swap-guide-for-your-usdm-2002-2005-wrx

Thanks everyone for the advice so far.  Very helpful.  I think I'll go with a VVT engine as you're suggesting.   And yes,  I plan to disassemble and clean the 99 head before putting it on anything.  It may end up on my Miata-swapped MGB/GT, which has a 1994 engine (I forgot that one makes 5 cars that can use this engine).  Keep the tips coming!

My current project is a 93 that was set up for turbo.  The 1.6 motor let go and I sourced a 2005 motor/trans and FM Happy Meal clutch.  Along with a parts shell of a car for $1000.  Parted out the remainder of the parts car and sold off the Happy Meal assembly and the VVT motor and trans ended up costing me zero dollars and a bit of time.  Of course VVT controller, ignition coils, MS3, and many other things are adding up.  As they always say, in an engine swap the cheap part of the process is the motor itself.

The NB heads have to use NB intake manifolds unless you want to do some screwing around with a-dapter kits. Keep that in mind for your MG - life will be easier if you have the same number of heads and intake manifolds. Nothing you can't handle of course.

In reply to Keith Tanner :

Thanks for reminding me.  I knew that once, but the knowledge keeps falling out of my head when new knowledge comes around.

Carl Heideman said:

Thanks everyone for the advice so far.  Very helpful.  I think I'll go with a VVT engine as you're suggesting.   And yes,  I plan to disassemble and clean the 99 head before putting it on anything.  It may end up on my Miata-swapped MGB/GT, which has a 1994 engine (I forgot that one makes 5 cars that can use this engine).  Keep the tips coming!

Just think of all the oil and grease free wiring you will get to enjoy.  I'm sure Keith can help you get ECU pin outs for both the old and new to help with the upgrade.  Heck it might even be documented online already.  I had quite a bit of fun upgrading my 84 Mustang SVO to run on an 88 turbo coupe ECU.  It was worth the effort.  That webpage might even exist in an archive somewhere.  I look forward to seeing this completed.  I'm strongly considering upgrading my LT1 F body (96) to run on LS1 coil on plug and an LS ECU.  

No need to swap the ECU - the stock 2001-05 ECUs are a lot fussier than 1994 ones, so I wouldn't do it normally. Probably twice as many wires, mostly talking to complicated things for monitoring emissions, but the bloody things even think they have to regulate the alternator. There are external VVT controllers, that's a lot easier in this situation.

That said, my 1990 Miata is a 2004 from an electrical standpoint. But it also runs an aftermarket ECU which lets me sidestep the fact that all the OBD-II stuff isn't there.

IIRC, the NB2 ECUs also have the immobilizer (theft prevention) circuit, which is problematic in an engine swap situation.

Also true. There are ways to deal with it but it's one more hassle.

Quick update:  I found a VVT engine that is supposedly from the UK with 60K miles on it and has the "flat top" intake manifold.  I wasn't actually looking for the UK/"flat top" but the first engine I found happened to be one and it belonged to a guy we autocross with.  It should go in this weekend and get fired up without the VVT or COP.  I'll address those in the future.  I'll probably put up a build thread with some dyno results along the way as well.  And David thinks maybe we should put something in GRM about it too.  Thanks for the advice and stay tuned.

99 engine is out. 

Oil pickup tube keeps rod from being completely ejected from engine!

In reply to AnthonyGS (Forum Supporter) :

When EvanB's #1 rod became #1.a and #1.b (I think - memory hazy) it broke everything in a 180 degree arc around the crank centerline including the oil pickup tube.  Most exploded engine I'd ever seen in person.

Can't find the pics anymore.  It was glorious.  The neat thing was, the big end was not only still on the crank, but it turned freely.

Welp.... if all else fails...

https://youtu.be/xgj35A8CpLA

lmao

In reply to Carl Heideman :

It's not supposed to look like that. 

Carl Heideman said:

99 engine is out. 

 

Yes, but how do you know that THIS is the real problem?  I'd keep diagnosing..

More gratuitous carnage pictures follow, but here's the quick backstory on the junk engine.  I bought this car a few years ago.  It was somebody's track rat and the engine let go.  Another guy bought it and rebuilt the engine at home, and I bought it cheap from him supposedly 50 miles on the rebuild.  Within a few miles, things started coming loose and rattling.  It was like he had everything finger tight.  I'll tell the whole story when I put up the build thread, but I went through the whole car, sorted it out, and dialed everything in.  After a few autocrosses, the engine had a tick/rattle at around 3500 RPM but then it would go away at higher RPM.  I went through everything external on the engine, including the water pump, timing belt tensioners, etc.. It was a good thing I did because one cam was one tooth off (which explained why it was down about 5HP when I baseline dynoed it).  Since I couldn't find anything externally causing the rattle, and it went away at higher revs, I rolled the dice for a few years.  The car ran a lot of autocrosses and 3 or 4 track days so it did okay.  I once had an MGB that had a similar tick/rattle in its engine and it ended up being a cracked piston that eventually let go.  I think that's the same thing that happened with this engine.  The #1 piston broke and took out the #1 crank journal and put a few holes in the block as well as the oil pan.  But the bearings looked fine.  

And it's back together and running again.

Here's a picture of the '99 intake next to the UK flat top intake for those who are interested.

I've got the '99 coils running the car for a few days until I get the pigtails I ordered from Ballenger Motorsports that will let me run the COP setup from the VVT engine.  You'll also see I opened up the wiring loom so that I could connect the cam sensor--it's at the front of the intake cam on the '99-00 engines and at the back on the VVT engines.  I'll of course make this all neater soon.

I'll dyno the engine with this coil pack, the COP (don't expect a difference), without the VVT, and with the VVT and put that all in the build thread as this work continues. In the meantime, I thought this last update would maybe help with a few details for others doing this swap.
 

Maybe this is the last update before I make the build thread...I got the pigtails from Ballenger Motorsports and made adapter cables to run the COP setup.

Things are good, except I'm getting a random misfire between 3500-4000RPM every now and then that seems ignition related since the tach drops when it happens.  It happened with both coil/plug wire setups, so I'm looking at ground connections and other issues related to changing the engine.

Check the air gap on the crank sensor. You could get this behavior if it's borderline.