Are JDM Engines Good?

When upgrading, fixing/repairing, or otherwise modifying a car, you might have the opportunity to purchase a JDM engine.

But are JDM engines any good?

In this edition of Car Facts, we are going to look at the pros and cons of using a JDM engine in your car.

NB: For the purposes of this article we are NOT looking at the pros and cons of JDM cars as a whole, but specifically using a replacement/aftermarket JDM engine or motor in your car. For example, you might have a Toyota Celica that was sold new in the United States, and you want to put a JDM engine in it. 

Why Would You Even Need A JDM Engine In The First Place?

As alluded to above, the most common reason you might be looking at buying a used JDM engine for your car is because your current engine is broken (e.g. blown engine) and you need to replace it. 

You might also be looking at buying a non-running car that needs an engine – or something along those lines. 

Why Might You Want A JDM Engine?

There are a few reasons you might want to use a JDM engine in your car over buying something “domestic” 

• Availability/cost
• Improved performance
• Prestige/cool factor 

No matter why you want or need a JDM engine, let’s look at whether or not they are actually any good.

But before we do that, we need to clarify a few common misconceptions: 

What Does JDM Mean?

If you want a more comprehensive breakdown of what JDM actually means, then read our JDM meaning guide.

However, for the purposes of this article, suffice it to say that JDM refers to “Japanese Domestic Market” – I.e. something that was originally made for sale in Japan and not for the export market.

What Is A JDM Engine?

If JDM stands for Japanese Domestic Market, then it stands to reason that a JDM engine is simply an engine that was originally fitted to a JDM car. 

Let’s say you have just purchased a Mitsubishi 3000GT VR-4 (of course only after reading our Mitsubishi 3000GT buyer’s guide).

Unfortunately – as old cars can have a habit of doing – after six months the engine blows.

Finding a replacement engine from another sold-new-in-the-US 3000GT is proving to be a challenge.

However, as luck would have it, plenty of 3000GT VR-4s were actually sold in Japan as the “GTO Twin Turbo”. There are some major difference – e.g. steering wheel being on the opposite side of the car – but mechanically the cars are largely the same.

You might then be able to find a “JDM engine” from a Japanese-spec GTO Twin Turbo to go in your car.

Sounds great, right? 

Are JDM Engines The Same As “Regular” Japanese Car Engines

Sometimes JDM-spec engines are exactly the same as those used in export vehicles that were sold new in countries like the United States, Australia or New Zealand.

Sometimes they are different.

Depending on the exact make, model and age of both the engine and car in question, there can be anything from no difference whatsoever through to some fairly substantial differences. 

The best thing to do is actually conduct some research about the engine you are considering buying. 

Are JDM Engines More Powerful? 

One of the reasons why JDM engines are a popular option for buyers looking to replace/swap out their engine (for whatever reason) is that many believe JDM engines are actually more powerful than their export equivalents.

But are JDM engines actually more powerful?

Often not.

Typically, if there is a small HP difference reported between a JDM and export version of the same engine, this can often be attributed to a different ECU/tune and also to the fact that the octane rating in Japanese fuel is generally higher than in many other countries. 

A good example of this is the 2ZZ-GE from the Toyota Celica.

In American/USDM trim, the Toyota Celica “GTS” had 180hp. However, the JDM equivalent (Celica SS-II) had 190hp. 

This whopping 10hp gain is due to a different ECU setup, allowing for different environmental restrictions in Japan and also the fact that higher octane fuel is more readily available.

Another example is the 20V Blacktop 4A-GE Toyota engine that was used in many hot Toyotas from the 1990s.

When tested outside of Japan, this engine typically produced anywhere from 10-15 fewer HP than claimed – the primary reason being that in export markets most testers were not using 100 RON fuel like Toyota had used.

Also don’t forget that on paper, many of the most powerful Japanese cars from the “golden era” of the 1990s/early 2000s were limited (on paper) to 276hp. Learn more about the 276hp gentleman’s agreement here.

Therefore – at least on paper – a USDM 300ZX twin turbo engine is actually more powerful than a JDM Fairlady Z engine!

Of course this limit is widely accepted to be total BS and was never really enforced, but still something to consider. 

How Do JDM Engines Come To Be Exported?

All this sounds very interesting and appealing – but it begs the question of how these engines even come to be exported out of Japan in the first place?

One reason that JDM engines are relatively plentiful is that Japanese motorists are basically forced by government legislation to upgrade their cars on a periodic basis (primarily to keep the car industry propped up, although ostensibly also to ensure safer and more efficient vehicles on the road).

This means that there is a thriving market of cars that were sold new in Japan, but after a relatively short period of time – usually less than five years – these cars are ready to be sold off to overseas buyers as the original owners have gone and bought new cars again. 

For various reasons, some of these cars might be better suited to parting out than selling whole – which provides a source of JDM engines. 

Believe it or not, Japanese drivers also do things like crash their cars or otherwise write them off, which one again means more engines are available for export. 

Are JDM Engines Reliable? 

Typically-speaking, a JDM engine will be as reliable than a “domestic” version of an engine from any given car, if the engines are basically the same. 

The idea that Japan keeps its best quality/reliability engines for the domestic market is a bit of a myth. You aren’t going to be buying some unicorn engine that is magically better than whatever was originally fitted to your car. 

However, it is always worth doing research on differences between export and JDM versions of any engine you are looking to buy. It is also worth researching the general reliability of the engine you are looking to purchase, as well as any known issues or problems (although this might be a moot point if you are looking to fit to a car you already own). 

JDM engines have a reputation for typically being more reliable due to lower-than-average mileage. The counterpoint to this is that Japanese driving conditions can often be harsher on an engine than you might see in countries like the United States, where cars will typically have higher mileage caused by lots of highway/freeway driving (whereas in Japan stop/start and low speed driving is more common). 

Ultimately, reliability is going to come down to the general reliability of the engine type you’re buying, as well as the condition and previous service history – which you probably won’t have access to – of your JDM engine replacement. 

You also want to make sure that you are buying your JDM engine replacement from a reputable vendor with a good track record. From our research, there seem to be a lot of “fly by night” operators who are buying inferior engines out of Japan, setting up a basic website and business presence, and then flogging the engines to unsuspecting customers.

If you want a reliable JDM engine, we would strongly suggest asking in specialist forums/message boards relating to your particular car (or at least make/brand e.g. Toyota) as to who is a recommended supplier. 

Pitfalls Of Buying A JDM Engine

In terms of potential problems with buying a JDM replacement engine for your Japanese car, here are some issues you might encounter:

• Higher than claimed mileage – Many used JDM engines claim to have low mileage, often in the region of 40-50,000 KM (X miles). However, you typically won’t get much in the way of paperwork or evidence for that sort of mileage, and it will be hard to discern exactly how many miles your new engine actually has done. Ultimately mileage is less important than condition, but if there are engine components that need replacing at a certain mileage and you’re trusting the claimed mileage figure, this could be problematic. 
• Worse than claimed quality – You don’t have to look too far online on forums and message boards to find plenty of example of aspiring JDM engine buyers who’ve had their fingers (or perhaps more accurately wallets) burned, thinking they were buying a mint condition engine only to find that what they received was not what was described. 
• Incompatibility – This is perhaps the biggest potential issue with buying a JDM engine and assuming it will just “drop in” to your car. Depending on the car, some engines will. For example, we understand that with a Mazda 3 MPS (read our buyer’s guides here) you can just drop in a JDM engine – there is no difference between a US and Japanese spec engine, and the process should be straightforward. However, take a car like the Mazda Miata – a JDM spec “Roadster”/MX-5 engine will need work in terms of wiring, ECU etc to work correctly. Even some of the internal engine components are different. Without knowing what car and engine you have, we can’t give you more specific advice – but definitely do your homework and research on message boards/forums/YouTube to see what difficulties others have encountered by trying to fit JDM engines. 
• Emissions/environmental legislation – Some jurisdictions have stricter emissions/environmental rules than others (here’s looking at you, California). A domestic specification engine might be tuned or modified from the factory to comply with pertinent legislation, whereas your JDM replacement won’t be. You don’t want to install the engine and then find your car is ordered off the road after emissions testing. 

Alternatives 

• Buying a “your market-new” engine – Let’s imagine you have a DC2 Honda Integra Type R (or actually an Acura Integra Type R) and you need a new engine for it. One option is to try and find a JDM one, but have you looked for any “domestic” engines in your local area or that could be transported to your location? One advantage of buying locally is that you might even be able to go and inspect the engine first if it is at a wrecker’s yard or dismantler. 
• Engine rebuilding – Sometimes it is “better the devil you know”. By the time you go through the rigmarole of sourcing, buying and fitting a used JDM engine, it might be possible to have your existing engine repaired or rebuilt for a similar cost. In doing so, you might even be able to get improvements or upgrades done at the same time.
• Changing engine altogether – If you’ve got a blown engine and you want to go “all in” consider whether the opportunity is right to do a proper engine swap. For example, if you’ve got a 3S-GE MR2, could you drop in a 3S-GTE and turbocharge your car? More work and complexity is involved, but if you’re already spending 75% of the cost on putting the same engine in the temptation must be there to do a proper upgrade. 

Recap – Are JDM Engines Any Good?

If you need a replacement engine for your car, then a JDM engine (for your Japanese vehicle) might be a good choice. Emphasis on the might.

Are JDM engines actually good?

Yes, they can be. 

However, from our experience and research, there seem to be a lot of potential JDM engine buyers who place particular emphasis or subjective value on having a “special” engine that was once used on the streets of Japan.

This, in turn, leads to overpaying over complicating the process of sourcing a new engine.

Lots of buyers also seem to overlook calculating whether or not it is better value to simply rebuild their existing engine, or source locally (I.e. from a “domestic” car) and jump straight to assuming that anything JDM = good.

We are definitely not advising you against buying a JDM engine as a general rule. Many car owners have done well for themselves and saved money by purchasing a JDM motor. However, many have also had a less-than-satisfactory experience.

If you’re going to buy a JDM engine, then the most important thing to do is your homework:

• Do your homework on who you’re buying your engine from. Do they have a good reputation? What is their policy if the engine isn’t as described? Is there any form of warranty?
• Do your homework on the engine itself. Is it a “straight swap” or will you have to make modifications/tweaks? Is the JDM version more or less powerful? 
• Do your homework on the cost side of things. Are you really better off from a financial perspective by buying JDM? Or would it be better to rebuild your existing engine, find something on the domestic market, or even consider a full engine upgrade? 

As long as you’ve done your homework, then JDM engines can be good.

However, where people encounter problems is just by going out and buying one because they automatically assume that JDM = better. This just isn’t the case.

JDM might be better. But it could be worse.

Do your homework/research, and you’ll have a much better outcome! 

What has been your experience with buying a JDM engine? Do you think they are good, or overrated? What is your buying advice? We would love your input – just leave a comment below.