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Nine Japanese Engines with the Worst Engineering Failures

Forget the Greatest of All Time. These May be the Worst in History.

Updated October 3, 2018

Most of the time everyone wants to talk about the GOATs (Greatest of All Time) and debate which engine they’d swap into their favorite ride if money was no object. Would it be a Nissan RB-series from the famed Skyline GT-R? What about the Toyota 2JZ from the iconic Supra? Both are probably on everyone’s top engines list, but the elephant in the room that no one wants to talk about are the engines that couldn’t dream of showing up on a GOAT list. These are the engines that are debated as the worst Japanese engines of all time because of poor engineering.

Honda D-Series (single cam with VTEC, 1.6L)

Worst Japanese Engines - Honda

The buzz initially started with the JDM dual cam VTEC engine which was accompanied by the hope that it would make its way across the pond to the US market. Sadly, it never made it with the dual camshaft formula.

The Honda Civic EX and Si arrived with a single camshaft VTEC engine when it started selling in the US market. It was definitely a step up from the DX and LX trims with the non-VTEC engine, but it seemed to be stuck living in the shadow of the DOHC VTEC of the Japanese domestic market. As many tried to make the single camshaft engine a real performer, they instead found every weak link in the engine. Those links included the connecting rods and smaller bores in the block, and anything standing in the way needed to be upgraded if you wanted to get significant power from the engine.

The aftermarket did give everything it could to make the engine scream, but as most found out the hard way, it was almost necessary to simply swap the engine with a better model if you wanted to have a shot at making more power.

Mazda 13B Renesis

Worst Japanese Engines - Mazda

The Mazda RX7 had a huge fan base which was deeply saddened when the RX7 left US shores in 1995. Nine years later, that fan club waived the banner that a new RX platform was coming in the form of the RX8 with the 13B Renesis naturally aspirated engine. The cheers didn’t last long, though, as the Renesis turned out to be a real dud. The engine touted a reduction in power to aid in miles per gallon, but even that started to sour as owners screamed foul on the MPG ratings. It turned into an all-out uproar and Mazda went so far as to buy back some RX8 models to satisfy their consumers. The aftermarket did put together some forced induction options, but the cost was hard to justify as the performance couldn’t really compete with any modified import in the same class. The Engine Management System seemed to fight against the changes anyway, and most RX8 owners chose to abandon ship to another chassis with some leftover heartburn.

Nissan KA24E (2.4L, single overhead cam)

Worst Japanese Engines - Nissan

The Japanese market 180SX and S13 Silvia were a huge hit in Japan and sparked a wave of attention from US consumers when the US version 240SX made its way across the pond. Fans of the car were sadly disappointed when they learned that the turbocharged engine in the Japanese models had been replaced with the single camshaft engine common with the Nissan Hardbody truck. The engine did provide significant torque, but couldn’t muster the power of its cousin from Japan. The iron block would hold significant power with forced induction, but the single camshaft just wouldn’t cooperate as much. Fans of the 240SX chassis were happy after two years of dull performance when the dual camshaft KA24DE replaced the single camshaft E engine. The E and DE engine are still referred to as a “truck engine” 30 years later, a stigma that will probably never go away. This engine suffered from too much hype and anticipation over marketing and couldn’t deliver on the promises.

Toyota 4A-GE (non VVT head)

Worst Japanese Engines - Toyota

The Toyota Corolla AE86 had a great Japanese professional driver in the 1980s and subsequently started a legion of new fans of the 4A-GE and Corolla when the anime series Initial D started in the early 2000s. Fans flocked to pick up the chassis and build capable drift cars as seen in Initial D, but most were disappointed in the 4A-GE engine once they realized how wimpy it was in real life. Thankfully, the AE101 chassis introduced a variable valve timing (VVT) head atop the iron block, but the new chassis had no RWD option to match the new potential with. The aftermarket began to upgrade to individual throttle bodies, replace the throttle bodies with carburetors, or swap the new VVT engines into the older AE86 chassis to combine the new promising engine with a RWD option. Others left the engine as it was and went the forced induction route unless they moved on to another chassis and abandoned the AE altogether.

Toyota 1MZ-FE

Worst Japanese Engines - Toyota 2

The Toyota 1MZ-FE engine started with a lot of promise. It was used in a wide range of vehicles from the 1990s through the mid-2000s, and even had a supercharger kit available from Toyota Racing Development. The aluminum block contained steel sleeves and was topped with a variable valve timing head (VVT) that showed it had a lot of potential. In 1996, the engine even made Ward’s top-10 best engines list.

As many owners found out the hard way, though, not keeping a steady eye on maintenance and oil changes proved costly, as engine sludge build up sent a number of these Japanese engines to an early grave. If engine sludge didn’t affect the engine, another killer proved to be head gasket failures with cracks in the aluminum heads that caused overheating issues.

Consumers eventually started a class action lawsuit because of the engine sludge and overheating issues. The engineers didn’t take into account their consumer wasn’t going to keep to a strict plan of oil changes, and that mistake cost the engine its place on the best list and sent it to the worst list.

Toyota 7M-GTE

Worst Japanese Engines - Toyota 3

The Toyota 7M-GTE engine was brought out with the 1986 Toyota Supra and carried into the 1992 release. The inline six-cylinder was a later variant of the 5M and 6M series engines, and the ‘T’ in ‘GTE’ stood for Turbo. The 7M showed an increase in displacement up to 3.0 liters and was meant to really put the Supra up against other factory supercars from JDM automakers. The 7M-GTE started to show reliability issues with failed head gaskets and knocking connecting rods when boost was dialed up on the factory engine, which would later be phased out come the introduction of the 1JZ in the 1993 Supra.

Nissan QR25DE

Worst Japanese Engines - Nissan 2

The Nissan QR-series engine was the replacement for the beloved SR and the mediocre KA engines. It ranged in size from a 2.0L to a 2.5L, and was used extensively in Nissan’s global lineup. One of the variations was the Sentra SE-R Spec-V in the US market which showed a sign of weakness in its peak of popularity. The Sentra SE-R used the 2.5L variation common with the Altima 4-door sedan and featured an integrated catalytic converter that suffered from poor ECU tuning on Sentra models.

The Altima didn’t suffer the same issue, but it did have an issue with piston rings over the course of its life that didn’t translate back to the Sentra. Sentra issues also showed up as higher oil and water consumption for consumers, as well as loose screws on the intake plenum that would find their way into the engine combustion chamber for a meeting with the pistons and valves. The piston ring issue on the Altima did spur a recall campaign, but the Sentra didn’t see similar action.

Subaru EE20 (Boxer Diesel)Worst Japanese Engines - Subaru

The Subaru EE20 Diesel was supposed to be a complete innovation of the famed Boxer engine that Subaru fans already loved. The diesel engine was released in Forester and Outback models and was advertised with lower emissions (38% fewer hydrocarbons and 60% lower carbon monoxide) over the competitive gasoline engine on the same models. Diesels produce significantly more soot than a similar gasoline engine, and in order to burn that soot out of the exhaust particulate filter, they needed to be run at full operating temperature for longer periods of time.

However, engineers didn’t take into account that their target market lived mostly in town and didn’t drive consistently at full operating temperature. As the mostly urban drivers found out, their catalytic converters weren’t being purged as regularly as the engineers planned, and converters soon plugged and needed replacing. The aftermarket tried to get around the problem by adding performance chips, but that opened a Pandora’s box that also caused the direct fuel injection to make holes in the engine pistons.

Mitsubishi 4G54B

Worst Japanese Engines - Mitubishi

The Mitsubishi 4G54B had a lot of promise but failed to deliver the goods. It sounded great on paper; it featured computer-controlled fuel injection and a single turbocharger, but it was hard to tune for more power and was prone to head gasket failures. Two fuel injectors behind the throttle body provided fuel for the engine, but this positioning showed trouble with equal distribution to all cylinders.

The throttle body, intake manifold, and cylinder head couldn’t flow enough air to really make significant power. The aftermarket never embraced the 4G54 enough to build and tune past the flaws and fans started to move on to the 4G63 engine which was much more capable.

As easy as it is to quickly blame poor engineering and design for all of the noted engine failures, one of the hardest things to design for is the end customer. While some designs look great on paper, the customer is the one who proves that the design is capable of performing as it is intended.

If their behavior is not part of the Design Analysis Matrix, the end result can and will most likely suffer in the customer’s hands. Engineers are problem solvers by nature, and they learned a valuable lesson with these ill-fated Japanese engines:

It’s easier to design a mousetrap based on customer behavior than to train your customer to use the product as it was designed for in the first place.

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Chris Riley
About Chris Riley

I have been wrecking cars for as long as I've been driving them but I keep coming back for more. Two wheels or four, I'm all in. GearHeads.org gives me a chance to give something back to the automobile community.

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