The "Mini" RB26DETT

Daihatsu J-Series : The monstrous engine nobody knew about, for obvious reasons. It has everything all legendary engines have, except displacement.

Steve Edward posted in Jdm
1y ago

We all know Nissan's RB-series, Toyota's JZ-series, and Mitsubishi's Sirius 4G63T. You know, the overengineered engines that put out some crazy numbers of horsepower. We've seen the videos all around Youtube. All the Supras making 800hp on stock internals, R34s making 1000hp on the same block that came out of the factory, killing supercars all day long.

But somewhere in Japan there was an engine that had the same capabilities to a lot of power without having to swap the entire engine. It had all the characteristics and everything that made the 2JZ & RB26 so legendary. There was just one catch, and you'll see why.

The RB26 Of The Kei-Car World「軽自動車界のRB26」

No, this is not something I made up. Enthusiasts in Japan actually called this the RB26 of the Kei-Car World.

And it's not surprizing to see why. Look at the architecture and how the engine was built and you'll see the similarities. Let's put out the stats. The headline is 168hp/ liter stock. Or to put it in a different way, the Mk.4 Supra would need to make 504hp to have the same hp/ liter.

The car was a special homologation car for rallying. The Engine was made of cast iron like the 2JZ. It had a closed deck block for that extra strength. ( if you don't know what a closed deck block is, click here ) The engine came standard with forged internals. It made about 17 psi of boost and the engine doesn't stop until about 8000 rpm.

It all sounds really good, for now at least.

The One Catch...

It's a 713cc engine.

Yes, this overengineered race-homologated engine with forged internals has less than 1 liter of displacement. The maximum power? 120hp.

The car? Daihatsu Storia X4. You probably never even heard of it. It came to Gran Turismo, but I assume the JDM exclusive car with a bulletproof engine you guys were driving was the R34 Skyline GT-R.

So how did this car came around?

The year was 1998. The goal was to beat Suzuki in the All Japan Rally at the <1000cc class, the lowest displacement class there is to compete in.

At this point you might be asking, "why is there a 713cc car competing in a 1000cc class?" Well there rules were that if a car was turbocharged, the displacement would be multiplied by 1.4 times. Hence the reason why the Storia X4 had 713cc. ( 1.4 * 713 = 998.2 ).

The car itself isn't anything special. No spoilers, no fancy widebody fenders, no rally wheels or even anything that gives the Storia an aesthetically pleasing look. If Mitsubishi made the Evo the same way it would look like your standard, everyday Lancer, albeit with the 4G63T engine. It looks like a standard Storia ( or Sirion in Europe ) that has a 1.0 or 1.3 liter engine. The car was never even good looking to begin with.

But it had 4WD, a bulletproof engine, LSD, and a stripped out interior. Enough to compete in a rally event.

A blurry history

The car and the engine didn't really have much presence. It was for the most part a race car, and Daihatsu didn't even bother to sell them to the public. You could buy it, but only from a special order. It would take 3-6 months just to get the car. By the end of it's production life, only about 800 Storia X4s with the JC-DET engine was ever made.

It was said that the engine could take 35 psi before blowing up, but I haven't found any dyno of the car at that spec. The car came with 17 psi +- 3 psi of boost, but owners who put boost gauges on found that the car made more than that. Some say at 25 psi with exhaust and intake mods the tiny 713cc engine would get 170hp.

It's really hard to find tuned versions or dynos or even anything about this car. It was such a rare thing to begin with. To see the car on on full boost killing supercars on the drag strip would just be a tale of legends we'll never see. Or is it?

The Alternative

In case you didn't know, this is a Daihatsu Copen. It's a tiny roadster with a happy face in the Kei-Car class with a 660cc engine making 63hp, also made by Daihatsu from 2002 to 2012 ( and it's also my dream car, FYI )

And you might be asking, "What does this car have to do with the Storia X4?"

Remember when I said that the JC-DET was the "RB26 Of The Kei-Car World"?

Well, if you know Kei-Cars like I do, you'd realize that the Storia X4 isn't a Kei-Car. Kei-Cars are limited to 660cc and 63hp. Size is also restricted to the size of a toy car. And clearly, the Storia doesn't tick any of the boxes.

And this is where the Copen came in. The spec? Kei-Car spec, 63hp. The engine? JB-DET, the engine the sister engine to the JC-DET.

The JB-DET another engine from the J-series. It's basically a de-stroked, non-race version of the JC-DET. No forged internals, no gigantic turbos* ( *by Kei-Car standards ), nothing too fancy about the engine when it left the factory.

But what it retains is what gives is the capability to exceed the Storia X4. The same cast iron block with closed deck architecture remains, and the tiny engine remains the rev-happy engine it once was. ( 8.5k stock, 9k with D-Sport ECU )

Looking at what was removed and what remained, there's a lot of potential for tuning in this tiny car. So tuning people did.

Maximizing The Potential

While aftermarket support isn't as crazy as Toyota's JZ-series or Nissan's RB-series, there's a lot to be made from the tiny JB-DET engine. HKS made a kit that would boost the car back to 120hp. You could get forged internals, bored pistons, and beefy camshafts from the Aftermarket.

There's not a lot of tuners for the Copen compared to GT-R, Supra, Evo, and other JDM cars. But those who tune, they can really tune.

Race-Spec Copens get their displacement bumped up to 820cc. Still not a lot, but when your engine is bulletproof and your car weighs almost half as much as modern performance cars, you're in a good position.

A Copen tuner Mo-Fac managed to squeeze out 225hp ( or about 274hp/ liter ) from their purple, widebody Copen demo car ( the one shown above ), and that's before NOS. ( they just recently installed them )

In case you want to know what a 820cc 225hp car sounds like, here's a clip of it.

While the JC-DET remains a legend, the JB-DET still hits the track until today in the first generation Copen, competing against cars with double and triple its displacement in Time Attacks.

While being an unknown engine to the rest of the world, it has some presence in Japan. It certainly is the most powerful Kei-Car engine I've ever seen. The engine remained bulletproof and what people are doing with it shows.

The Copen itself isn't much of a hardcore sports car. The majority of Copens sold were in fact equipped with a 4-speed auto. ( around 65% or so ) But with the lightness of the car, the agility of the Kei-Car size chassis, and a bulletproof JB-DET engine, somehow it just becomes a good chassis to build a track monster.

The End of The J-Series

The JB-DET, the entire J-Series engine, and the first generation Copen ended altogether in 2012.

Came to replace was the K-series engine. A 3 cylinder engine with a cast aluminium block instead of iron to reduce weight. With the oncoming trend and demand for efficiency just didn't leave a room for the more performance-oriented 4 cylinder JB-DET.

But as we know all stories must come to and end. And where one story ends, another one begins.

And who knows, the KF-DET engine in the second generation Copen is already making 164hp, maybe we'll see more crazy power figures from 660cc engines somewhere in the future.

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Comments (6)

  • Welcome to DriveTribe Steve! Great Article!

      1 year ago
  • Someone should join two blocks to one crankshaft and make a crazy little V8

      1 year ago
  • Great article!

      1 year ago