NC Miata 2.5 conversion: Talk me down? or...?

I know there's content on Miata.net and have been perusing that too.

I have a '06 NC Miata with a death rattle somewhere in the shore block portion of the #1 cylinder. Checked by a good shop and with another trusted shop as a second opinion. This is supposed to be my daily driver, but has been sidelined because of this issue. I want factory reliability and reasonable fuel economy (would love the ~28+MPG I get with the 2.0)

I could have the 2.0 rebuilt. But it looks like the Mazda/Ford Duratec 2.5 as real close to a drop in swap, has more power, more torque, and is cheaper than rebuilding or replacing the 2.0! Weight is close to the 2.0 as well if balance shafts are deleted.

I'm on the East Coast - south central PA - and am really leaning towards having a shop do this rather than taking a lot more time than I really have at the moment. My son has done a successful 1.8 -> 1.8 (younger engine) swap in his Miata, but I'm not real confident in tackling this and getting it completed in a timely manner...

Talk me down or not...? I'm pretty sure the end goal is the right one for this car, but not sure of the best way to get there. Your thoughts?

Sounds like a great fathers son project but understand if you literally don't have the time. I'm not going to talk you down, 2.5 swap sounds like a no brainer.

I don't know about 2.0 to 2.3 but the 2.5 has a taller deck height. That may throw all sorts of monkey wrenches into the works, not just for hood clearance but also the exhaust system and possibly intake plumbing. Maybe. But the exhaust may be a PITA of bracket redesigning and possibly some pipe work, and we're hoping it clears the hood.

None of this is insurmountable, of course, but "having someone else do it" means you are going to pay someone else $80-120 per hour to do it. Time adds up fast for this kind of thing, especially if it's not something they have done before so they are learning as they do it.

Most shops would just say "No".

If you can get it to pass OBDII inspection, I don't see why not provided that the transmission would bolt to it.

Transmission is a boltup, there are suppliers with $80 or so engine mount replacements covering the hood clearance. That's more for keeping weight low though - it looks like it would clear the hood regardless; I'm not the first one to do this. There are apparently some (minor) issues with mixing 2.0 / 2.5 intake components to get things working sufficiently, and aftermarket to do more than that (not looking for more though).

No emissions where I live, but I don't see any reason it would NOT pass OBD2.

99% sure the exhaust bolts up with one clearance issue that needs to be addressed on a 2.5 ancillary part.

It's not as easy as a 1.8 swap on an early car. It's also not as easy as the various forum threads would have you believe. Do NOT use poly motor mounts unless you want to make the car very unpleasant.

It's also an undersquare long stroke truck engine. The 2.0 isn't exactly a revver to start with, the 2.5 less so.

It's not my favorite swap.

Not to counter Keith here as he is a miata yeezus but our shop just finished one. Drove it Friday as a matter of fact. To me it's a riot, but we mainly run spec miatas so we are always itching for a few horsepower here and there. This swap produced roughly 30+ hp and torque across the board on our dyno. Compared to an ls swap it obviously wouldn't hold a candle but I felt it maybe the power level that the NC should have had from the get go.

Some disclaimers... we did put a set of cams in it which may have helped a little in the "truck engine" compartment that Keith had mentioned. We did of course have to dyno tune it which, if you don't have access to one, can be expensive. And it was pretty straight forward for us, but we work on miatas day in and out so depending on your skill set it may not be.

They gentleman that had it done wanted something reliable that he could run at the track and having a weekend fun car. It's got ohlins suspension etc and this guy has had plenty of track time. Pretty sure he loves the you know what out of it. If your motor is dying anyway, then doooo it. Just my 2 cents.

Oh and p.s. if you don't mind getting it down to s.c. we could definitely do it for you. I know it's far though. PM if your interested and I will get you in touch with the boss.

Oohh yeah, I forgot an important thing in my post.

On a four that large, don't delete the balance shafts unless you are a paint mixer enthusiast. They may be 20lb or whatever but that is sanity weight, like mufflers or sound insulation or wheel weights. It's a small percentage of the car's total weight but you REALLY notice if it's not there.

Do a KLZE

https://www.youtube.com/watch?v=toughTZ9PIw

Is't that the same engine the Pirelli World Challenge Miata's use?

Having never owned a miata or an MZR powered vehicle, I cant comment to this specific swap, but I can comment to the truck engine comment, since most of my stuff has been SBC powered, which is probably the most prolific truck engine there is.

Id be willing to bet the 2.0 head and some aftermarket cams, with a nice header on a 2.5 could make that truck engine a hoot to drive. The LT1 went from a high rpm weezer with a torque peak at 2500 rpm, to a 7000 rpm screamer, that came on the cam so hard it would blow the tires off halfway through a third gear pull.

All Im saying is a "truck motor" with some mods can be fun, you get the extra torque from the cubes, and you can run more came and get similar driveability. My vote is for the 2.5 is it isnt much extra work.

Knurled wrote: Oohh yeah, I forgot an important thing in my post. On a four that large, don't delete the balance shafts unless you are a paint mixer enthusiast. They may be 20lb or whatever but that is sanity weight, like mufflers or sound insulation or wheel weights. It's a small percentage of the car's total weight but you REALLY notice if it's not there.

Having just ended my 5-yr-long successful relationship with just such an installation, I can safely say that it's really not that bad. Yes, the NVH pretty much sucks but it's not unbearable.

However, if I were doing it over again I'd probably keep the balance shafts.

It's not a "truck motor", it's a truck motor. It's what you'll find in the current Ford Transit Connect, for example. The Ranger, the Escape as well. The undersquare design is always going to make it more of a chugger than a screamer. I'm sure you can work around to some extent.

It's certainly a popular swap (in forum lore if not in fact), and we've got a car here that I think would benefit well from it given some of the other mods under the hood. But overall, it's not my favorite swap.

I would not want to pay a shop to do it for the first time for the reasons that Knurled stated.

Keith - isn't it also one of the regular engines used for the Mazda 6 and Ford Fusion?

In my shoes - keeping in mind the goal is low cost, low running cost high reliability continued daily driver use, what would you recommend? The 2.0 costs more and there doesn't seem to be a benefit to stay with it...

These guys do a lot of the them and can get you everything you need parts wise:

http://dynotronicstuning.3dcartstores.com/Engine-_c_238.html

I've driven 3 of them. Stock, one with a PPE header, and the full package with the Cams, Exhaust, Header, and tune.

You will need a re-tune and to do it right, you'll spend 4-5K. Just doing the swap without the adders is uninspiring at best. Add the full package and it's a great street motor.

http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=25303

How about the 2.0 Ecoboost? Looking online dealers are asking $5500 for the package. Did you read the first four bullet points? Especially the fourth?

I think the biggest issue is the location of the high pressure fuel pump hanging off the back of the head.

I believe Keith said Flyin Miata investigated it but I'm not sure I ever heard any outcome.

Yeah, it's used in family sedans and minivans as well.

In your case - when you're paying someone to do the swap - I'd drop a new 2.0 in it. IIRC, they're not terribly expensive. Less than a rebuild, and less than paying someone to figure out how to deal with the fact that your new 2.5 hits the hood and the exhaust is up against the trans. This is an opinion, obviously the 2.5 has caught the attention of the internet so it's the best thing ever.

We did look at the Ecoboost. Not to the point of buying one. It's not a priority around here. Contrary to what the internet has decided, we are not a swap everything! shop, we pick one or two and do them really well. And we have to be able to make a living at it.

We've also done a 2.5 swap, and determined that either the guys doing them for money are working for $10/hour or they're not doing a complete job.

jstein77 wrote:

Knurled wrote: Oohh yeah, I forgot an important thing in my post. On a four that large, don't delete the balance shafts unless you are a paint mixer enthusiast. They may be 20lb or whatever but that is sanity weight, like mufflers or sound insulation or wheel weights. It's a small percentage of the car's total weight but you REALLY notice if it's not there.

Having just ended my 5-yr-long successful relationship with just such an installation, I can safely say that it's really not that bad. Yes, the NVH pretty much sucks but it's not unbearable. However, if I were doing it over again I'd probably keep the balance shafts.

I may be a weenie, but I "filled" the torque mounts in my Volvo and the vibration at idle is way too annoying. Shaky idles are acceptable for an 80s POS but modern cars should be dead smooth.

I also have read some interesting articles re: balance shafts in Evos and transmission life.

Does the supercharger kit for the 2.0 fit the 2.5?

From my perspective I say do the swap. While I love a good high-revving motor torque is way more fun.

And assuming the 2.5 being discussed is the one used in the newer Fusions and such, it's not like it hates to rev a bit (although I personally find the thing a little bit rough and coarse, mostly in sound, especially at low rpm).

Keith Tanner wrote: It's not a "truck motor", it's a truck motor. It's what you'll find in the current Ford Transit Connect, for example. The Ranger, the Escape as well. The undersquare design is always going to make it more of a chugger than a screamer. I'm sure you can work around to some extent. It's certainly a popular swap (in forum lore if not in fact), and we've got a car here that I think would benefit well from it given some of the other mods under the hood. But overall, it's not my favorite swap. I would not want to pay a shop to do it for the first time for the reasons that Knurled stated.

I just said "truck motor" because although yes it is availble in some "trucks" so is the 2.0. It was available in the Transit connect and the Cmax. That and I dont think it matters much, some of the most loved performance engines that were produced by mainstream manufactures made their way into a truck in some form or another.

And for a street motor, Ive never really bought into the whole over-square/under-sqaure thing. Yes in a high end competitive racing series it will probably matter, but not so much on the street. Some very good high revving engines are under square like in the Integra Type R (B18whatever) or the E46 M3 (have no idea the engine desgination).

If you gave me the choice between and over or under square 2.5, I'd take the over square engine, and probably just for the bigger bore and its affect on head flow, but I would never give up a fifth of the displacement to move from an under square to over square engine for the street.

DaveEstey wrote: Does the supercharger kit for the 2.0 fit the 2.5?

Yes, but you start to hit the limits of the blower so most of the gains are at the low end.

FWIW, back when this engine family first came out- there was an actual difference in a 2.3l Ranger engine and a 2.3l in a car. The ranger had shorter and lower cams just to "help out" the low end.

Today, I don't actually know if there still is a cam difference between the 2.5 in all of the vehicles.

Other than that, there was a very small deck height difference in the 2.3 vs the 2.0.

(ok, ignoring the intake and exhaust design differences, but those seem pretty obvious- as they are 100% package driven)

Relative to the NC Miata- it's pretty likely that Mazda has a nice set of cams for that specific engine.

Still- if you are going to do this swap, that means some tuning needed, and if you are going to have to do that, might as well spend a few more bucks for a decent cam swap.