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Going inside: the strengths and weaknesses of popular performance engines

12 May 2019



Out there in the world, there’s a million and one engine combinations for you to drool over, and, regardless of what they started as, you can guarantee that, at one time or another, at least one person out there will have tried to squeeze a little more power out of each. While some lesser used packages may remain a mystery, you’d think there’d be a simple recipe for those more commonly used examples; however, it can still prove a hard task to get the right combination when it comes to rebuilding those more popular examples the way you want them.

The joys of the wealth of information that is the Internet have meant that everyone and anyone can have their say, whether it’s sworn truth or blatant lies. For those seeking answers, it’s become a matter of filtering out the gems from the trash through trial and error — and that, for the most part, is a risky way to approach one of the most expensive components in any car, only amplified when you’re looking to push serious numbers out of it. Put the phone down, turn off your laptop, and stop posting on Facebook help groups. What you’re about to read will save you valuable time, and hopefully some money, too. We’ve constructed a list of the most commonly modified engine packages found out there today, and put them forward to the experts who spend their days fine-tuning the art of engine rebuilding — all just to get you the scoop on that juicy insider information that no amount of googling is ever going to reveal. You can thank us later.

Subaru EJ20

There’s no denying the attraction of the throaty rumble (single-scroll only) and gravel-carving prowess upon which the humble Subaru EJ20 has built its name. The 16-valve horizontal flat-four is the mainstay power plant in Subaru’s engine line-up, and can be found in more generations of Impreza, Legacy, and Forester than any other combination on offer from the automaker. For the majority of the EJ20’s 30-year production run thus far — starting in 1989 with the BC5 Legacy RS and still found today in Japanese-market WRX STis — it was offered as the top-spec JDM option, while most export markets received a variation of increased capacity EJ-series hearts. In that time, Subaru continued to develop the configuration and implement a series of technological improvements that see the later generations more popular than earlier incarnations.

Patrick at Possum Bourne Motorsport (PBMS) tells us that the best EJ20 examples can be found in STi models, especially the W-block from the JDM V11 Impreza GRB. Although availability is limited and prices remain high, which means most people lean towards earlier ’90s-spec GC8 models or V7-9 GDB due to cost and availability, and the most common that PBMS works on come from V7 and V8.

“The V7–8 engine is a good upgrade over an older non-AVCS or open deck design EJ20. As far as the block goes, these came with factory-forged pistons and are a semi-closed deck block. They also offer better ignition with the coil-on-plug, the heads have good size ports in them, and the V7s were the first to come out with AVCS [active valve control system] on the inlet valves,” explains Patrick. “All these things make it quite popular to put into older cars or even building upon the generation they came out in. A new short block can be purchased off the shelf from Subaru, too, but most people tend to rebuild the factory motor instead.”

Comparatively, despite the bad wrap they tend to get for being ‘unreliable’, the EJ20s have very few issues that need to be addressed when being built. The main thing that PBMS sees is big end bearings failing, typically caused by insufficient lubrication, so the most common thing that is done while the motor is apart is to modify the internal oiling system with their PBMS oil gallery modification to address the problem. Narrow bearing surfaces make the EJ20 sensitive to lubrication and detonation issues, so PBMS recommend using a baffled sump for spirited drivers and all motorsport applications to ensure there is always oil at the pick up. Patrick also stresses that this can usually be avoided through regular maintenance and having mechanical sympathy for the car.

“A big thing is regular oil change intervals and using quality grade oil. We run Motul here, and service every 5000km. Don’t change the oil every 20,000km and wonder why it’s run a bearing. Also, warming the car up before thrashing it and making sure the oil is always topped up properly, just things like that — it’s cheap insurance.”

Another aspect that may often be overlooked is running your vehicle with a quality tune to achieve optimal air–fuel ratios and preventing tune-related detonation. When chasing a basic increase in power, PBMS recommends focusing on ensuring the internals can support any bolt-on upgrades. A good starting point is forged pistons and rods, machining the block and head surfaces, likewise machining the valves and seating surfaces, and upgrading the valve springs as well as head studs. That will set you up with a good base to push more boost into with a larger turbo over the factory unit. For those wanting to get serious, a W-block goes well, and factory stroker builds can easily be achieved, or having PBMS perform their closed-deck modification that is available for all EJ20s, 25s, and EZ30s to strengthen your existing block to support high-power and boost applications. While EJs tends to be synonymous with rally, you can find them in almost any discipline and, being a boxer with a low centre of gravity and paired with a good four-wheel drive system, they tend to go pretty well. The trick is to make sure that people who know what they’re doing are charged with piecing your EJ20 together, which is a good rule for any performance engine build!

Possum Bourne Motorsport / 09 238 5732

Nissan RB25DET


Since its inception back in 1991, and first launched in the GTS-25, the RB25DET has been a favourite of engine tuners the world over. Offering a 2.5-litre capacity and stout single-turbo power figures — with a factory-rated 186kW in series-one form and 206kW as a NEO — they became popular conversions in earlier model Nissans, including finding their way into a number of non-Nissan chassis. Locally, they flooded into the country in used imports, commonly in R33 GTS-25Ts and Stagea RS/RS4s, and remain a staple of the Nissan world today.

John from Hamilton Cylinder Head & Engine Reconditioners explains that when hunting out a good example to base an engine build off, the NEO units are usually preferred for their higher power output and expandable capabilities, although carry a higher purchase cost. You also have the option of starting with the naturally aspirated version and putting boost through them, as the long-block itself shares many of the same characteristics. However, John warns, this route is only good to a certain point and can be troublesome if pushed too far: “The RB25DET has oil squirters in the block and a lower compression ratio that is friendlier to receiving boost, but are, for obvious reasons, more expensive. RB25DE engines, on the other hand, are more plentiful, and can still make good power as long as the boost is kept lower, to suit the higher compression ratio, and ensuring they are tuned correctly. Leaning on a DE motor too heavily, especially one that hasn’t been forged, will often result in premature expiration.”

As far as their popularity goes, John puts this down to two simple factors: the first is that the aftermarket support enjoyed by the RB25DET is very large, upgrade parts are easy to find, and there are a number of proven combinations that will make good, reliable power. The second is that they tend to be cheaper than other options within the category, such as the 1/2JZ-GTE.

However, there is a common issue that can be found within, and one, if unattended, can lead to serious failures, usually resulting in total loss. John explains: “The oil pump drive on the crankshaft is small and prone to wear. When this becomes worn, it is less effective and over time will reach the point of failure, causing loss of oil pressure, and serious internal damage. When rebuilding an RB25DET, we always recommend addressing the crankshaft oil pump drive collar, either replacing it with a new OEM example or upgrading it to a performance-oriented unit, especially when you start pushing for more power.”

For those looking to squeeze more power out of their own engines, or thinking about acquiring a long-block for their next build, John says it is a pretty straightforward path to achieving a good result. “For a stage-one upgrade, we would typically look at high-flowing the factory turbo for better response and top end. At the same time, you’d open up the exhaust and intake for effective in-and-out flow, and larger injectors to ensure the fuel quantity is there to match. These can easily be tuned through the use of a Nistune piggyback ECU and using a factory Z32 300ZX airflow meter. Anything further and you’re looking at opening the bottom end up and installing forged pistons and rods, while upgrading the rod bolts and head studs, all to make sure that boost can be put through the motor without concern for failure.”

And while you tend to find the RB25DET competing in the likes of the national drifting championship, and used in numerous street cars, John says that units that they have worked on have gone on to campaign hill climbs and compete in circuit racing series to good results.

Hamilton Cylinder Head & Engine Reconditioners / 07 847 8470

General Motors LS1

All our readers should be more than familiar with the LS series of engines. They’ve carved out a juicy segment of the modified automotive scene as the

go-to choice for V8 conversions, and are found in practically any chassis you can think of — none more so than the LS1. The first of the Generation III

small-block V8s, there are thousands of ‘junkyard’ LS1s waiting to be plucked from the wreckers and shoehorned into engine bays across the world. The Americans love them; they’re in all manner of Japanese metal over there, thanks to their use in a series of Corvettes, Camaros, and Trans-Ams. As they were ported over into Australia’s own Holden line-up — and you only have to take one step outside your front door to see how popular Holdens are on our shores — we’ve got a tonne of them here waiting to go, too.

Scott from GER Engine Specialists comments that, when it comes to picking which LS1 to start with, factory power figures can range from 220kW to 285kW at the flywheel, depending on the model.

“The LS1 is most commonly found in the VT-VZ Commodore / HSVs that were manufactured between 1997 and 2007. The pick of the bunch is a Callaway modified version that is fitted to the 2000 HSV GTS VT2, which boasts a claimed 300kW, although these are hard to find as only 100 were made.”

Regardless of which you opt for, the range has a number of benefits over Japanese variants, which is undoubtedly why the LS1 is so widely used.

Scott explains: “Being a 5.7-litre V8 with all-aluminium construction and two valves per cylinder, the LS1 is a very light, compact unit as opposed to the likes of Toyota or Nissan V8s, which have four valves per cylinder plus double-overhead cams, making them externally larger and [consequently] making them a tighter fit in engine bays in comparison. The Japanese equivalents are also smaller capacity, and can lack low-to-mid-range torque, only coming alive at high rpm, whereas the LS has a very impressive ‘out of the box’ performance — not just power but torque as well.”

These characteristics give the LS1 greater drivability and usable power, not to mention that there’s an almost endless supply of genuine and aftermarket parts available for performance upgrades. This availability gives you greater options when building an engine or making upgrades to external components, to suit both performance required and your budget range.

Scott recommends changing the cold-air intake to a good-quality aftermarket option and likewise a free-flowing exhaust system as a good stage one upgrade. He also tells us that a dyno session to reflash the ECU would top it off. Each modification on its own shows some good gains, but all three together provide the best results.

Scott observes that, like any engine, the LS1 does have its weaknesses, with camshaft wear and lifter failure being the major concerns.

“Like other variants of the LS engine, the LS1 can suffer from camshaft wear and lifter failure, even though they are roller cams and lifters, so it would always be a good idea to replace these while you’re rebuilding the engine as a preventative measure. This also gives you the opportunity to upgrade to performance-orientated components for better performance, even if it’s just upgraded valve springs with a standard camshaft, as, over time, the fatigue on them can lead to breakages or loss of tension.” Scott also mentions that being an aluminium block and partially open deck, the bores tend to suffer from distortion and ovality over time, plus there’s usually general wear as most examples would have endured a reasonable amount of mileage by now.

“New pistons and rings can be supplied in .005-inch, .010-inch, or .020-inch oversizes, depending on the wear or distortion in the bores,” he explains, “and we would always bore and hone these using a torque plate for greater precision. Besides the usual bearings and gaskets that you’d do on any engine, we would always replace the timing chain, gear, and oil pump on the LS1. The chain and gear are a single-row arrangement that will wear and stretch over time. You can upgrade these to a double-row set-up for performance applications, and oil pumps can be supplied in either standard replacement or for performance applications, high-pressure or high-volume options depending on what is required from your specific build.” Given that the LS1’s lightweight, all-aluminium design can produce solid power and torque characteristics straight off the bat, plus the magnitude of aftermarket support, the LS1 and its larger variants have found their way into a huge range of motorsport classes. Scott says that, depending on a customer’s requirements or that of the class they are competing in, the LS can serve across almost any motorsport, including circuit, drag racing, jet boats, drifting and off-roading.

GER Engine Specialists / 09 818 5352

Mitsubishi 4B11

The 4B11(T) is a special one, in that it’s a lone example in the Mitsubishi Evolution’s long-running line-up of predecessor 4G63 power plants. Found exclusively in the Evolution X, the 4B11 is a two-litre, straight-four turbo that was the first to use an all-aluminium design versus the cast-iron blocks found in previous models. It weighs 12kg less despite the introduction of MIVEC continuous variable valve timing on both the intake and exhaust cams, and the switch from a timing belt to a chain-driven system. Being found in a model that was still selling at dealerships only a few years ago, stand-alone examples are in short supply, but if you’re looking to develop the 4B11 inside an Evo X, there are huge benefits to having a modern power plant.

Most of the 4B11 engines built locally have been from the development by Dustin NG at DNG Automotive — an Auckland workshop that specializes in race car development and preparation — in partnership with Harris Performance Engineering.

Alan from Harris Performance Racing explains that the 4B11 camshaft system is more conventional and modern in the way it operates, with a cam acting directly on flat tappet followers sitting on top of the valve stems: “With the 4B11, the follower can never leave its place under the cam, and with a shimless system to set tappet clearances, there is no shim to jump and cause bent valves or worse,” he tells us. “With the flat tappet follower system we also enter into the same set-up as most other factory turbo engines, like the RB and 2JZ. This simplifies custom cam selection, as previous development from other engines we have built can be applied with reasonable confidence in the effect on the power and torque curves. This allows us to select cams of various lifts and durations to achieve the desired powerband and drivability that matches the purpose of the vehicle.”

As far as the bottom end goes, Alan tells us that the cranks seem good, though, as seen with the previous 4G63 and even the VR-4 V6 engines, the rods aren’t substantial enough for much more than the standard power output: “As in any performance build you would want to make sure the rods and pistons are up to the task of what you are going to do with them. We really believe that you get what you pay for when spending money on core items like rods and pistons.”

“You have to get someone who knows what they’re doing to sort out the bearing clearance and oiling system when installing forged rods and pistons; there’s issues with the oiling system that need to be sorted out before trying for more power,” explains Alan. “The springs in the standard cylinder head don’t like being pushed, either; we’ve found all the standard valves to be questionable as soon as you start using them in competition, even with the standard tune. We’ve had to solve a few issues for customers buying and running them in Targa.”

For those looking to squeeze a few more ponies, Alan says the best gain in performance and reliability can be had through dealing to the head: “We machine the cylinder heads as accurately as we can to ensure sealing of the valves and reliability of all the parts. We then port the heads to our own special port shapes to increase the quality of the flow through the ports. This leads to much improved spool-up times and a huge gain of area under the torque curve that makes the car much faster in acceleration than its peak power figure would suggest.”

“Most of the DNG Automotive and Harris Performance Racing Mitsubishi motors are built for rally or endurance events such as Targa or NZ Rally Championships where the motor has to make quite a lot of power over many hours of use, sometimes over many seasons of racing.”

Harris Performance Racing / 09 534 3363

DNG Automotive
38E Lunn Ave / 027 416 9569