Forum Users, Please help me to update/sort through/add-to/correct the information below.
I expect that I have left some things out, and the unfortunate truth is, I have probably given a bit of misinformation somewhere. The goal of this thread is to identify the differences in drivetrains between the years, and to identify the parts that are expected to fail as someone increases power, as well as the corrective measures to implement.
Thanks!

 

It seems like every single day, I’m having to harass a newb that posts pics of his new Miata, and says “I’m coming from the world of (insert name of sports car that produces >250 hp stock here) and I’m looking to make a conservative 300hp”

Frankly, it’s sickening. If I have just described you above, to the “t”, then you need to go take a humble pill, and come back with an open mind. I’m not saying it’s impossible, but I AM saying it ain’t easy.
So what needs to be replaced to make 200/300/400/100000 hp? Just tell me already, HOW DO I DO EET!?!?

 

First thing’s first: You need a Miata.“But I’ve already got one…”
Shut up and read this part anyways, it’s good background information that you’ll use.

NA 1.6
In 1990, (1989 actually) Mazda came out with this cute car called a Miata. Now don’t ever use “cute” when describing this car again, or I will take your man-card. The engine that was used in this Miata was designed for use in the turbocharged 323GTX (that’s right, the engine was designed for a turbocharger right from the start, all the way down to an oil feed port) This means, that the engine takes well to boosting from the get-go. Unfortunately, short nose crank problems (not power related) plagued the earliest cars, and the rear end is prone to grenading. Both of these problems can occur at stock power levels. Greddy introduced a complete kit for the 1.6L cars, and is an effective and cheap solution to running low levels of boost. You will also replace every single part of the Greddy setup in any upgrade path, so if you plan on bigger goals, buying a Greddy kit ensures that you WILL do it twice. If you have no further plans, a Greddy is cheap to find used, and for the liberals, it’s even CARB approved. The 1.6L weighed about 2100 lbs.

More information on the short nose crank. Miata.net Garage Thanks Samnavy!
Bottom Line: All '90s were subject to the problem. The separation point for '91s is vin numbers 209446 - 209447

NA 1.8
In 1994, the car was upgraded to 1.8L displacement. Mazda replaced the 6” Ring and Pinion with a 7”, which would be common to all 1.8L cars. The viscous limited slip was replaced with a much more desireable TORSEN T1. The basic construction of the car stayed the same, even retaining the 1.6L connecting rods, which become the first weak point in adding power to the 1.8L engine. In 1995, the only change which is significant to you is the switch to a fake oil pressure gauge. Mazda did this because of retarded people. It seems the average consumer has been trained to believe that oil pressure is always the same, and is afraid the ******* moon is going to crash into the earth when they see their oil pressure gauge move. If you think something is wrong with your car because the oil pressure drops when the car warms up, or because the oil pressure goes up when you step on the gas, then we can all thank people like you for making Mazda dumb down the Miata. You’re a ******* moron. Starting in 1995, your oil pressure gauge does not show your actual oil pressure, it only answers the question: do I have at least 8psi of oil pressure? The new oil pressure gauge is effectively “broke” from the manufacturer. If you have a ’95 or later, you will need to find a new way to monitor your oil pressure. In 1996, the only change which is significant to you is the switch to OBD-2. If you live in a state with plug-in computer inspections, this is going to be a headache for you. The OBD-2 continues through all 1.8L models 1996 to 2006. The NA 1.8 weighs around 2250 lbs.
1998 Model.
In 1998, Mazda produced the only time-traveling car ever made. These were supposed to be released in the United States and probably Canada. None have ever returned from testing, and as such, a North American 1998 model never actually made it out of mazda quality control.

NB1
1999, to increase the power, Mazda redesigned the intake system. The intake manifold and cylinder head were drastically redesigned. The complete exhaust tract (valves, ports, manifold) is physically unchanged (A ’94 exhaust system will bolt up to the 99 head) with the only change being the EGR connection (and the actual EGR system). If you will be deleting the EGR anyways, you won’t even care about this change. The ’99-’00 cars have a “returnless” fuel system, which makes it slightly more difficult to manipulate the fuel system. ’99-00 cars changed the location of the camshaft position sensor from the rear exhaust cam to the front intake cam. A different physical sensor is used. In 1999, Mazda introduced the 10AE car. Among several insignificant alterations, Mazda introduced the 6-speed transmission. It was standard equipment on the 10AE, and optional on all cars starting in MY 1999. The 6-speed transmission is proven to hold substantially more power than the 5-speed transmission. The NB cars weigh around 2350 lbs.

NB2
In 2001, the car underwent another design evolution. The cylinder head was changed again, and now incorporated infinitely adjustable variable valve timing (VVT). VVT offers serious potential gains in efficiency and power, but adds a degree of complexity. To see the gains, the ECU must be capable of tuning the VVT. The oil pump was also increased in volume, though only barely, to add flow for VVT. The new larger oil pump then superceded the NB1 part number. The differential was changed to some off brand, but the change is insignificant. The NB2 continued production until the NC was introduced in 2006. The NC shares no parts with earlier models.

Mazdaspeed Miata (MSM) 2004-2005
The MSM is the factory turbocharged Miata. It runs a ’99-00 cylinder head (eliminates VVT). The 6-speed transmission is standard (Mazda touted the MSM transmission as being shot-peened, and as such it is believed to be stronger, however, no evidence exists that non-MSM 6-speeds are not also shot-peened, and there is no evidence of non-MSM transmissions breaking where a MSM wouldn’t.) The Mazdaspeed is factory equipped with stronger axles, and the differential is designed with larger output splines to accommodate. Because of this, MSM axles and MSM differentials are compatible with one another, but not compatible with their non-MSM brethren. The MSM differential mounts to everything else in a stock 1.8L miata, including driveshaft. Non-MSM rear axles are usually only a weak point in extremely high powered (400+ RWHP) drag cars. The strength of the actual R&P is thought to be similar to that of non-MSM models.

 

List of outstandingly undesirable traits.
'90 to early ’91 – Short Nose Crank
’90 to ’93 (All 1.6L Models)

• Reduced Displacement vs. 1.8L models
• Weak 6” Rear End
• Viscous Limited Slip Differential (Where Applicable)
• Smaller Brakes
• Smaller Clutch

’95 to 2005 (All Models) – Fake Oil Pressure Gauge
’96 to 2005 (All Models) – OBD-2
’98 (All Models) Time-Travel generator only works to travel to the future, traveling to the past didn’t work (Information is suspect)
’99-00 (All Models) Returnless Fuel system

List of outstandingly desireable traits.
’94-02 (Applicable Models) and '04-05 (Mazdaspeed only) – Gear biased limited slip differential
’99 up (Applicable Models) – 6-speed Transmission
’99-00 and MSM (All Models) Better flowing cylinder head
MSM – Stronger rear axles

List of notable traits.
o ’01-’05 (All Models except Mazdaspeed) VVT Cylinder Head (In transition from being “undesirable” to being “desirable” due to the increasing ability of ECUs to actually control the VVT. If your ECU can control the VVT, you want VVT.)
o ’01-’05 (All Models) Slightly higher flowing oil pumps to support VVT. (Aricjm15: MSM used the same larger oil pump)
o All model years had the option of open differential/limited-slip differential based on trim. When comparing two similar 1.8L cars, the one with the gear-biased differential is worth $600-$1000 more than the exact same car with an open differential. That is the market value for the swap.
o Faeflora: In 2003, Mazda introduced the "Tochigi Fuji Super" Limited Slip Differential in place of the Torsen T2. The differential is touted as being "torque sensing", but is simply a modern clutch type differential.
o MSM Differentials are Bosch torque-sensing units.
Miata.net Diff spotter's guide

 

Should I buy a car that has already been heavily modified or turbocharged?

There is no single definitive “yes” or “no” answer for this question, because one guy will be selling a pristine example of what a turbo car should be, and the guy across the street will be selling a heap that makes more power. When looking at buying a modified car which you are unsure on, the single best indicator that a car was built carefully by someone who knows what they’re doing is the “details”. Items like a large difference in front-to-rear treadwear, mismatched tires, missing lug nuts, and a dirty interior can indicate an owner who is lazy. Poorly fitting gauges, wiring rats nests, and an engine bay that is an eyesore are indicative of a builder who is sloppy. If you can open the hood and picture the engine bay in new condition, sitting on the dealer’s showroom floor, then you may very likely have found an excellent example of a car. If on the other hand, the engine bay looks like a high school student replaced a bunch of “look cool” stuff, you might want to be wary. In the end, the little details won’t show you if the motor has been abused, or if the engine has knock, or if the fueling system needs upgraded, but as I said previously, they can be an indicator of how much care the previous owner put into the car.

If you DO buy a heavily modified or turbocharged car, the first piece of advice I can give you is this: “DON’T DRIVE IT”
No, seriously. The previous owner built the car, but YOU are responsible for it. If you buy the car from someone, and the engine eats itself on the way home, you have no one to blame but YOURSELF. If you MUST drive the car home, don’t boost it. Drive it as if you know you have just enough gas to make it to your driveway if you feather it the whole way, and not a drop more. You need to understand all of the systems on the car, and you need to be fully convinced that the car has a proper tune. Basically, if the car is new to you, it is guilty until proven innocent. (Kinda like street racing tickets in California)

 

Now it’s time to get into the meat of things: the mechanical limits of your Miata.

1. The differential. If you’re running the stock 1.6 differential (6” ring gear) plan on blowing it up. Buy a stock ‘94/later diff + housing + driveshaft + axles, and bolt it all into place. The ‘94/later differentials are generally expected to hold about 385hp reliably; much more if you treat it well, much less if you wheel-hop.
Tips for doing the diff swap by SamNavy

2. The fuel system. On gasoline, 1.6L Injectors will be effectively maxed at 140-150 rwhp. 1.8L Injectors are a direct fit, and max out between 170 and 180 rwhp. To figure out what size injectors you want to purchase, see post 3 in the DIY FAQ. For a simpler, but cruder equation to find your ideal injector size, multiply your horsepower goals by 1.8, then round up to the next available injector size. This is the *minimum* injector size you will need to fuel your car at stock fuel pressure levels. Additional headroom is always a plus. The fuel pump is known to be adequate to somewhere around 300hp. A Walbro 190LPH HP is generally accepted as the upgrade. For more information on the fuel pump, see post 4 of DIY FAQ.You will be tuning for, and running premium fuel in a turbocharged car.

3. The clutch. If you plan to make more than 150hp on the 1.6, or 180hp on the 1.8, expect to replace the clutch. You can put together your own setup, or else buy an FM kit and be done with it. The larger 1.8L Flywheel/clutch/pressure plate assembly (all 3 pieces combined) is a direct bolt-on for 1.6 applications. If you buy a performance clutch kit with a new flywheel, you will get one based on the 1.8L design.

4. Cooling System. There are so many factors involved with the cooling system that it is nearly impossible to give a HP number where it needs to be upgraded/replaced. If you’re going to add a turbocharger, you’re going to introduce a substantial amount of additional heat into the engine, which must be removed via. the cooling system. The first recommended upgrade is a larger all-aluminum radiator. You will also want to consider adding higher flowing fans, though this is not always a necessity. If you’re a track rat who always runs a cooldown lap, it probably isn’t necessary to upgrade from stock. If you’re an avid autocrosser, you need to put serious thought into fans. Consider your specific driving habits. Pre-98 cars need to strongly consider a coolant reroute. Post-98 cars have a different head gasket that promotes a better OEM flow, but may also consider the coolant reroute by using the earlier head gasket. The heater core is a fundamental part of the OEM cooling system, and the coolant flow path must not be removed without serious consideration of the second order effects. If you absolutely must remove the heater core, you should re-join the two hoses so that the coolant flow path is maintained. You may insert a short length of smaller diameter hose into the heater core hose which can slightly restrict the flow of coolant, similar to the restriction provided by the heater core. If you simply cap off the pipes going to and from the heater core and do nothing else, your coolant will pressurize inside your engine, and you may begin blowing hoses and gaskets. If you're going to turbocharge the car at any whp, makes absolutely certain that your OEM cooling system is working efficiently. If you plan to make more than about 200whp, do yourself and your engine a favor and buy a high performance radiator and fans.

5. PCV. The PCV works because there is somewhat higher vacuum in the intake manifold on a stock car. Boost works by putting significantly higher pressure in the intake manifold. Think about that briefly. Consider replacing with crankcase ventilation that does not vent to the intake tract. Most users are running a VTA (Vent to Atmosphere) system, which routes both crankcase vent ports to a “breather tank” before venting to atmosphere through a filter. Some users are currently getting good results experimenting with VTE (vent to exhaust) setups which provide effectively unlimited flow capability while also drawing a slight vacuum (less than one PSI) on the crankcase. Again, there is no *must replace* number on this, as most cars will benefit from not inhaling crankcase fumes, but for the cost involved in making it work right, there's no reason not to fix this above 200whp.

6. The 5-speed transmission. This transmission is mechanically identical in every single car from 1990 to 2005. It is generally expected that they have a finite life span above about 250 hp. You have two options: Buy replacement 5-speeds all day at $75-150 a shot, or buy a stock 6-speed and be done with it until somewhere north of 400 rwhp. Track-junkies will see the life of 6-speeds decreased somewhat, but for a street driver/autocrosser, the 6-speed will very likely outlast the driver. The 6-speed is bolt-on for all NA and NB cars. Note: Because of the closer ratio gearing, running a 6-speed transmission will result in HIGHER freeway RPMs. To reduce RPMs, consider a ring & pinion swap.
For information on swapping in a 6-speed, visit: This link
For information on changing the ring and pinion (DIYable, exacting tolerances, outsourcing recommended if available): Miata.net Garage
For information on changing the speedometer in NA cars to match a new ring and pinion: Clicky

7. The connecting rods. 250 WTQ. Maybe a little less over time. This is the weak link in the Miata engine. Mazda used the same 1.6L rods when building the 1.8L engine, so there is no variance in the power-holding ability between 1.6/1.8. You have two options for improving the rods: (Thanks Jeff Cieleski!!)
-----A. Cheap aftermarket rods: Will ensure that you break EVERYTHING ELSE before ever having to replace a rod again. (Detonation not included)
-----B. Expensive aftermarket rods: Will put power down exactly the same as the cheap rods, but weigh less, mathematically improving power gains.

8. Ignition System: Expect to see spark blowout above 14psi, exceptions may be for stock COP (coil-on-plug) setups on ’01 and newer models, though I’m not sure on the limits of these. (Hell, I’m actually slightly skeptic of the existence of stock COPs – I’ve never looked under the hood of a stock NB2 car)
More information can be found in the COP Thread.
Also check out COPS For Dummies - A writeup by SamNavy

9. Stock Pistons. 300hp. This is not a definitive number, but rather a generally agreed upon value. Stock pistons are forged, but generally fail at the ring lands. Your options for pistons include compression ratio and price.
-----A. Compression Ratio: High compression ratios tend to offer better throttle response, as well as more off-boost power. The drawback is that higher compression ratios require a much more precise tune. More power is being made on lower compression pistons because of their natural resistance to knock relative to the higher compression pistons. Current members are running radical ignition timing on low compression pistons…with a safety margin...
-----B. Price differences: See item 7. (Connecting Rods) Above.

10. Oil Pump Gears. The stock unit uses sintered metal gears. These tend to fail because of the increased amplitude of the vibrations present in higher HP cars, which is further aggravated by the higher than stock RPMs that many of us run. Most cars are generally safe to somewhere around 320hp, some sooner, some later, you may want to consider a set of aftermarket oil pump gears based on how risk-averse your budget is. A failed oil pump will basically destroy the majority of moving parts in the engine. There are no documented failures of billet oil pump gears.

12. Additional Safety – Crank Pulley. Many high HP cars are running the Miata specific ATI Super Damper. The damper reduces crankshaft vibrations, especially at the oil pump, and can help increase the life of your spinny bits. Do not, under any circumstance, run an aftermarket “billet underdrive pulley”. The Miata engine will quickly shake itself to pieces without the vibration damping provided by the stock or aftermarket damper. Though not considered a *necessity* at any HP, consider it the *next step* after oil pump gears.

11. Axles. Drag cars on slicks break axles north of 425 rwhp. A mazdaspeed rear-end with thicker axles is one option. There are now kits to bolt much stronger GM and Ford rear-ends into these cars, along with axles that support much more HP than our 1.8L engines are capable of with current technology.

It should be noted that track beasts will have far more complex problems, mostly due to heat, regardless of horsepower.

 

Spot Saved

 

This entire thing is a great idea because it is geared towards people asking about turbocharging. Fortunately, there are already some awesome answers to a lot of the things you've put out. It's just a matter of getting people to clicky... for example:
http://www.miata.net/faq/

You need to look at that link and see where in your posts you can include links. For example, instead of saying this:
"Unfortunately, short nose crank problems plagued the earliest cars,"

Say this: Although not related to the engine's ability to handle boost, a specific run of cars that can be identified by VIN from the 90 and 91 model years frequently have a crankshaft issue you can read about here: http://www.miata.net/garage/crankshaft.html We just call it the SNC (short-nosed crank) issue.

When you talk about #5 and refer to tranmissions, a common question is whether you can swap a 6-spd to get a higher top-speed... we all know that 6th is actually shorter than the 5-spd 5th... but the gear calculator at the FM site will "show" people difference: http://www.flyinmiata.com/tech/gearing.php

The link to the gearing calculator can be found on the FM "technical information" page on their website:
http://www.flyinmiata.com/tech/index.php

There used to be a STICKY that I wrote up called "EVERY MIATA WEBSITE YOU'LL EVER NEED" that I think has disappeared... would be awesome to add the LINK to that thread if it still exists.

Bottom line... I could sit here literally for days to build a massive "Turbo your Miata for Dummies" thread... but if that thread existed, all we'd have to do was point every single NOOB towards it and then we couldn't make fun of them as much.

 

Great thread, can we ask questions? This should be on Wikipedia.

Does balancing the entire rotating assembly (bottom end only) change this?

 

You can balance it, but balancing will not take into account the impulses from the individual cylinder combustion events as these aren't mass related, but more specifically, they aren't constant. If you could balance out the combustion events at WOT and high rpm, your low rpm operation would have to contain significant vibrations.

Unless my physics is wrong.

 

fooger03 i think that this is a good idea but the path to power is very different between 200, 300, and 400+ hp. Ask me how I know :|

 

Your path looks like a pinball trying to get off of the gameboard at hands of the worlds best pinball machine player. I'm not aiming to educate innovators here :P

 

Dude my car works, makes power, and I do have a few innovationish successful mods like gutted IM with port WI, slashcut, bosch 044 in tank, PLX gauge system.

Part of your faq should include "how to not overbuild" like a certain someone who put in a built motor just to run a GT2560

 

RAWR!!!!
It's FMIIR Ready

 

There is a life that exists beyond a highway pull that lasts 12 seconds

 

With more power you would rescind that statement

 

So could you.

 

Sick Burn!

Can we post grammar comments?

I believe this could be expanded easily into the next realm of turbo miata noobness which is questions about turbos in general. How much power can I make with this turbo, are these turbos reliable, chinachargers, etc.

FYI I have found the best way to not be bothered by noobs on here. It involves being on this site less. If people want to be spoon fed, then spoon feed them or dont. Let whatever happens happen.

 

Ha ha someone build their engine and was running a gt2560?! lol that's too funny

 

The MSM shares the same oil pump as the VVT cars.