(From Issue 32)
The roots of the Toyota Supra can be traced back as far as the svelte Toyota 2000GT of the 1960s; cool enough for James Bond to cruise around in the movie “You only live twice”. The engine used in that car gradually grew in capacity through the years, as the long-lived M-series and it survived up to the 7M-GTE-powered Mark 3 Supra of the early 90s.
The first Supras were derived from the Toyota Celica, beginning in 1979 as a Celica-Supra. Having the larger six-cylinder engine, they have always been the more performance-oriented of the two cars. The method of making the Celica and Celica-Supra as similar cars continued up to the start of the Mark 3, where they finally got their own unique chassis. In the later years of the model, the JZ series of engine was introduced. This was then used as the only engine type in the final Mark 4 model.
Toyota put a huge amount of effort into making the Mark 4 Supra, the JZA-80, as good as they could get it and a pretty serious performance car for the enthusiast. The chassis, drivetrain, and suspension was based on the Z30 Soarer but everything else was unique to the new performance flagship for Toyota. The driver’s seat had a comprehensive array of instruments and switches placed around it so they could be reached easily in an arc that has echoes of a jet fighter cockpit.
The shape of the cockpit strongly favours the driver, leaving the passengers a bit out of the loop but let’s face it, who cares about them? They were graced with big beefy brakes all round. The Rz model was given even bigger stoppers, which it needed, as the cars massed about 1500 kg, which was a lot for a car of the 1993 – 2002 years that the Mark 4 was built. They would have weighed more but things like an aluminium bonnet, suspension components, etc, all helped to remove some of the excess. However, being based on a luxury car (Soarer, or Lexus SC300/400), they had many bits and pieces that all added up. As an example, the wiring loom was very extensive and makes up a good 25 kg of the total, with there being numerous sub looms and connectors that were used in the Soarer but not in the Supra.
Another weight saving was – believe it or not – the door hinges. If you get a chance, have a look at the door hinges on a Soarer as they are quite large and a work of art. They are designed to make the front of the door move outwards a bit instead of merely pivoting and the far end of the door not open quite as far as usual, so you can still easily get in and out of the car. However, even though the doors are huge, they don’t open too far in tight spaces.
The heart of the mighty Mk 4 Supra is the famous 2JZ-GTE twin-turbo straight-six three litre engine, a very tough Getrag 6-speed gearbox known by the Toyota code of V160, and an equally beefy diff equipped with a Torsen LSD. You’ve probably heard stories as to how tough those components are and how much power they can make; they are all likely to be true. The Supra also had the option of a naturally aspirated 2JZ-GE and 5-speed W-58 gearbox or a 4-speed automatic, but let’s face it, who cares about them? The diffs, by all accounts, are bulletproof with ratios of around 3.2 for the manual gearbox car and about 3.7 for the automatic.
The big, hefty Getrag gearbox likewise is extremely tough, with massive gearsets and bearings. They do, however, tend to leak oil and so the oil level has to be checked regularly. The legendary 2JZ-GTE is quite a remarkable engine with a reputation of being able to take large amounts of boost. From the factory, they come equipped with two small turbos. These don’t run in parallel but in fact are a sequential system; at low revs almost all the exhaust gasses go through just one turbo so it spins-up and gets on-boost very early. It works so well that at a mere 1,800 rpm the engine is making a full 300 ft-lbs and it never gets any less than that as the revs pick up. As the revs head towards 4,000 a valve opens in the exhaust system and the gasses start to spin-up the second turbo. It adds its flow to the system and so reduces the restriction that having one small turbo would have. Without putting a spanner on them, they make a solid 320 hp/ 240 kW, and with a very wide useful power curve they were a rapid machine right from the factory. Performance testing showed that they’d get to 100 km/h in just under five seconds; the 1/4 mile was smashed in only 13.1 seconds at 175 km/h.
The top speed recorded for the turbo was 275 km/h. Not supercar times, but certainly a very rapid machine with no modifications. Having ridden in a standard one, I am quite happy to say they feel every bit as fast as the numbers suggest! For a road car you wouldn’t bother getting any more power from them as it’s more than enough for anything you’d ever want. But how would be be if you took about 250 kg out of one and got the engine to make about three times as much power?
You may remember Peter The Welder from one or two of my previous articles. This one is about his own JZA-80 Supra. If I may jump straight to the juicy bits, he has taken a lot of weight out of it so it’s down around the 1280 kg mark now. The last dyno session had it making close to 700 hp at the wheels. Yes, you read that right. Seven. Hundred. Horsepower. At the wheels. The story of how this has happened will surprise you. To qualify for an article in this fine magazine, the car in question has to be used on the track. Road cars, no matter how cool, don’t make the cut and Pete’s Supra has done numerous track days at Queensland Raceway. After the further improvements that will be detailed later in this article, many more track days will be run …. and won.
This Supra is only the fourth car that Pete has owned and the first one that he’s competed in. It’s what’s called a “93.5” model and so one of the early production RZ models, with the ones made shortly after having the addition of air-bags. It was purchased as a Japanese import in 2000 and ran completely standard for nearly two years, then the modifications started shortly after Pete opened up his metal fabrication workshop.
Not one to think small, this is when the big single Garrett GT42R turbo was fitted as well as a 87 mm exhaust and Haltech ECU. In that configuration and ‘only’ one bar boost it made about 280 kW/375hp at the rear wheels. Not long after that, the current 100 mm exhaust was fabricated and fitted, then the dump pipe was also up-sized to 100 mm. Back in the early days of owning it, Pete spent a lot of time researching what people were doing with the Mk 4 Supras by reading the internet forums dedicated to them. Back in the early 2000s, the GT42R was a pretty big turbo. As people have found the limits of what the engine can do, it turns out that it’s about the smallest one you’d use these days for serious power. There are Supras in the US that run some exotic fuels, much larger turbos with 50 psi boost, and are reputed to make 1,500 hp.
The most recent configuration for the engine has had quite an amount of work go into it. Pete, being an excellent fabricator, made his own inlet and exhaust manifolds. The manifold is a work of art, with the six primary pipes initially sweeping down below the turbo then curving upwards into a dual collector that feeds into the turbo. The turbo is big enough that the compressor housing sits only millimetres from the strut tower. Exiting the turbo is a 100 mm diameter dump pipe and exhaust which exits from the left-rear corner of the car, again via a Pete-made rear-mounted muffler. The compressor gets its air from an 100 mm alloy intake pipe with a K&N air filter.
From the compressor outlet, a 63 mm diameter pipe passes the compressed air to an intercooler the size of a small suitcase tucked in front of the radiator. Both coolers have ducting to ensure that all the air that meets them doesn’t escape. From the intercooler, a 75 mm alloy pipe runs up to the inlet manifold via an adapted 70 mm 1UZ throttle body. The Pete-fabricated plenum is grafted onto the original lower factory inlet flange with 50mm tube runners.
To feed its prodigious thirst for fuel, the car has a set of six 1,000 cc/min injectors that are fed by twin Walbro fuel pumps that have been grafted onto the factory fuel pump bracket. It originally had an older model Haltech E6K for engine management but from about 2006, has been fitted with an Autronic SM4. This does a much better job as it can control the boost-per-gear and so make the car more drivable in the lower gears.
The clutch is a ‘direct clutch’ sintered brass unit that still allows for a bit of slip that is not too bad when it needs to be driven on the road. The head still runs the standard shim-on-bucket arrangement but has crower springs to suit the higher lift (9.3 mm) HKS 272° cams, to help it breathe and rev a bit better. The brakes are still standard, but being an RZ model, are quite large and capable of repeated stops from high-speed, though the brake pads do wear very quickly on track days. The suspension is again largely standard but with coil-over damper units, slow rebound adjustable, from HKS. Around the time the Autronic ECU was fitted, and the engine and gearbox moved back, the rear sub-frame also had all the flexible rubber bushes replaced with aluminium ones to try to eliminate the wheel hop at low speed when the inevitable wheelspin occurred.
Now, while all the above may sound like something from some kind of Hot Japanese Imports magazine there is a point to it; It’s what hasn’t been done that’s also of interest. The head is standard and unported, the block has never been opened, it’s got a completely standard oiling system, the pistons are standard, the head gasket is standard, the water system is standard (well up until recently), the flywheel is the factory very heavy dual-mass unit, and so on. Pete did a lot of research and chose wisely what he added to the engine to make it work well. The only inconvenience is the need to add Toluene (methyl benzene) to the fuel to protect the engine from pinging under the full two bar boost it regularly experiences. Things have changed a fair bit recently but I’ll get to that later.
The end result in that configuration is a bit of a monster to drive, as although it is still surprisingly flexible and torquey when off-boost, it’s nothing like what happens when the turbo erupts into life. The engine idles with a bit of a lump at just over 1,000 rpm courtesy of the cams but smooths out with any load on it. It has the characteristic six cylinder growl when revved though with little muffling it is very loud even without boost.
The turbo is just along for the ride until the revs get up around the 4,000 rpm mark, then you can hear the compressor start to really spin-up and suck air. It starts off as a whistling noise, then a few hundred rpm later that noise rapidly becomes a howl which is the warning that all hell is about to break loose. Another few hundred revs and the turbo is making boost – lots of it – and the world outside starts to become a blur and the shove in the back is like the wildest carnival ride you’ve ever experienced.
I’ve both passengered and driven the car and it’s difficult to convey with mere words just what a rush that amount of power is and how quickly things happen. When I was lucky enough to be able to take it for a short run for testing, I used fourth gear before giving it any throttle because it’s less likely – it doesn’t eliminate the chance! – of breaking traction. Since I don’t have any other experience with such a high-powered car I didn’t want to press my luck. In that fourth gear, I was doing about 130 km/h when the boost hit, and I swear that about two seconds or so later the 8,000 rpm shift light was telling me to pick fifth. Yes, it’s really that fast! When it’s up on-boost the scream of the turbo and wastegate dominates everything. You can still hear the engine though, also bellowing away and picking up revs much like it was in neutral with your foot flat on the throttle.
Pete has told me he’s seen 320 km/h in sixth gear and there were still revs and power to go. So we don’t actually know what the top speed would be, and there’s certainly no circuit in Australia with a straight long enough to find out. Other colourful stories include early day experiments with a pair of gearstick mounted microswitches to electronically limit boost in first, second and third gears. Whilst testing it, “… something went wrong and I got 8psi more then intended, and at 200-plus km/h it broke into wheelspin. That got my attention!”
Another, when he took the car to the drags with the new 315 tyres, as grippy as they were, there was still wheelspin for 2/3rd’s of the track.
In more recent times, Pete decided to make some other changes to try to improve the handling and the major modification for that was to move the engine and gearbox rearwards by 50 mm. Because the 2JZ-GTE and Getrag gearbox are pretty heavy in themselves, this would make a noticeable difference and help reduce understeer. Custom engine mounts with heavy duty rubbers were introduced – to allow the engine to be remounted and keep the turbo from clipping the strut tower.
Straight-six engines are inherently perfectly balanced with both primary and secondary harmonics so you can get away with firm mounts on a road-driven car. Having the engine further back also allowed for the intercooler be placed inside the engine bay along with the new alloy PWR radiator core. A Davies-Craig water pump was fitted, which disappointingly failed very quickly, so a new US-made Meziere pump was installed and has run faultlessly ever since. The rubber water plumbing was replaced with -20 speedflow hoses.
The alternator and power steering pumps have had their positions reversed for a better belt path as they are the only accessories left. The turbo itself is of interest as it’s a bit of a rare mongrel; It’s an early GT42R with a ball-bearing core and a 67/94 mm compressor wheel and GT45R 77/87 mm turbine wheel. The housings are more likely to be found on a truck, as the unit was a very early one and housings were very hard to come by, with the ones that are on it now the only ones available. The old-style 52 trim 0.7 A/R compressor housing casting has very thick walls and although the internal dimensions are the same as a current-type housing, the new ones have much thinner walls. Pete says, “You look at the latest turbos from Garrett and the ones that will easily make a thousand horsepower are actually a little smaller than mine.”
As I type this, the car is just a bare shell sitting on a rotisserie, with Pete removing all the sound deadening and tapping out a few lumps and bumps in the floor from years of street and track work. It’s also getting a repaint – remaining gloss black – and more pieces of the interior removed to reduce weight with a target of 1250 kg or better. (There’s 17 kg in just the clutch / flywheel and crank alone.) A pair of Kevlar seats will be the only luxury with only the shell of the dashboard left. A Motec SDL will take the place of all the old Toyota instruments.
A small panel of switches to run the indicators, headlights, and windows will be the only things left remaining. There’s no air-conditioning, radio, or any of the usual road car basics left. But the most interesting area will again be the engine and gearbox. Pete has decided to upgrade the venerable 2JZ with a 94 mm stroke crankshaft that takes it out to 3.4 litres. Even with the long stroke, the crank is a good 7 kg lighter than the Toyota original and by all reports are reliable up to a 9,000 rpm. The car is also getting aftermarket con-rods and pistons, again all lighter than the original factory items.
A lightweight Tilton flywheel and 7.5” carbon clutch assembly is coming and they weigh a full 10 kg less than the ones they replace so the engine response will be greatly enhanced by that alone. The Garrett turbo will remain, but with the larger capacity engine it will start to create boost a good 500 rpm earlier and so make the car a bit nicer to drive. Pete probably won’t be revving it much more than the usual 8,000 rpm though, as he says the “turbo starts to fall over at those revs”. This seems surprising due to the size of the unit so with the increased capacity some head work is going help reduce the restrictions that the rough Toyota ports used to have. It will run the same boost, as the car already has enough power for its use, but with the modifications it will be more controllable. In the effort to make that happen, some Motec M600 ECU trickery is going to occur with the boost maps so the turbo doesn’t hit like a freight train, and can hopefully be driven a bit smoother around the corners.
The old set-up made it very difficult to have the engine and turbo spinning fast enough when cornering and be able to work the throttle while exiting the corner without the usual World War Three melting the rear tyres. Pete says, “It’s hard to control the boost with the throttle with a turbo this size”, so hopefully with the improvements in the engine and management system this will allow him to work the throttle earlier in the corner, rather than having to either wait for the car to be straight before hitting the throttle or having a good guess as to how early to hit the throttle before the turbo comes on. Yes, that guesswork has lead to the visit of one or two sand traps when it didn’t work out.
To compliment the new engine is a very serious gearbox – a Hollinger RD6 – which is the same as the V8 Supercars currently use. This one though, will have wider ratios from second to sixth. First gear is the same and although quite a tall ratio it should still be able to be driven on the street to get to and from the track courtesy of the clutch, which with the latest modern materials allows for a bit of slip to get moving rather than the older ‘button’ type clutches. Fifth gear is 1:1 and sixth gear is 0.7:1 to allow for a bit of a quiet drive on the highway. Well, as much as a straight-cut gearset will allow for anyway.
The gearchange will be just like the V8’s in that the throttle can remain fully open during an up-change and this will make staying on-boost much easier and smoother. Speaking of the V8’s, don’t forget that this car will weigh a little bit less but have quite a lot more power at the wheels and so will be remarkably fast. One of the quirks with running a big single turbo is that they tend to lose boost quite easily unless you hold full throttle. Another surprise is if you keep the revs up around a corner, with the plan to have instant boost when you open the throttle on the exit, they often just ….. don’t, in Pete’s experience with his. You have to bring the revs up, hold the throttle, and then they go hard. With the electrickery of the Motec ECU in combination with the seamless Hollinger all that should be eliminated as much as possible.
Two Motec PDMs are also being fitted, one at the front and one at the rear, to vastly simplify the wiring and also reduce weight. There is a set of four KW double-adjustable coil-overs to improve the suspension as well. The current 10 x 18” front wheels and 11.5 x 18” rears will stay.
The plan is to have the car running again around the middle of next year. Then, after some sorting it will again hit the track to see how much better and faster it is. Whilst Pete is quite used to the power it makes, having driven it like that for the best part of a decade, the time I drove it really surprised me as to just how much poke it had. Knowing what’s going into it in the future, I think it will feel like it has every bit of a million horsepower.