This article was first published in June 2002.
So your turbo diesel Toyota Prado feels gutless, eh? That's no surprise considering it produces only 96kW and weighs nearly 2 tonnes.
But for a total cost of just under $1400, you can achieve a whopping 19 percent peak power increase, bringing the flywheel output up to around 116kW. Oh, and - get this - that's without replacing any hardware or touching boost pressure!
For those unfamiliar, the current 100-series Toyota LandCruiser Prado can be purchased packing a 1KZ-TE turbo diesel (the same engine often fitted to Japanese-import Toyota Hilux Surfs).
The 1KZ-TE is a four-cylinder in-line engine displacing a total of 3-litres and running a static compression ratio of 21.0:1. The bottom-end uses a 5-journal crankshaft with carbon steel (lightweight conrods) and fibre reinforced piston crowns. Breathing is through an 8-valve, SOHC alloy head, pressurised by a single turbocharger. A top-mount air-to-air intercooler (which is fed air through a double skinned bonnet) cools the maximum boost pressure of around 10 psi.
ECD (Electronic Control Diesel system) takes inputs from throttle position, rpm, manifold pressure, road speed, coolant temp, fuel temp and intake air temp sensors. Unlike many other diesel engines, the Prado's also uses an electronically controlled throttle and a complex TCV (Timing Control Valve) fuel pump arrangement to control fuel injection timing and quantity.
The 1KZ-TE's maximum torque is 343Nm at 2000 rpm, while maximum power is 96kW at 3600 rpm.
South Australian market gardener Frank Imbrogno purchased this automatic turbo diesel Prado TX in 2001 and soon grew frustrated by its lack of power. Overtaking, he says, was a painfully slow (and therefore dangerous) exercise, and steep hills also posed a challenge.
Frank began considering aftermarket power-up options and - after being impressed with the fitment of a UniChip interceptor in a friend's Volvo - he booked the car in at his nearest agent. Here's where we arrive on the all-wheel-drive Dyno Dynamics chassis dyno of Adelaide's Turbo Tune...
Baseline Power Output
This blue plot reveals the standard Prado turbo diesel generates 57kW at all four wheels. Look at the way the turbo diesel's torque curve begins very high but plunges almost linearly as revs rise. As a result, maximum power is attained at relatively low rpm. Note, however, near-maximum power is maintained throughout the entire lower half of the rev range.
Wiring In the UniChip
The first job is to gain access to the Prado's engine management computer, which is hidden in a tight space up behind the glove box.
Unlike most other UniChip interceptor installations, the Prado ECU then needs to be removed from the vehicle. This is to enable two connections to be soldered onto the board. This delicate task is necessary to complete the UniChip's wiring connections - 12V power, earth, TPS, manifold pressure, rpm input, and an intercept of the fuel unit's Timing Control Valve control.
Once fully wired into the Toyota loom, the interceptor module requires extensive programming, as there's no supplied 'base map'. David of Turbo Tune spent around an hour on the chassis dyno real-time programming the UniChip via laptop. He claims nearly 90 percent of its 408 adjustment sites were altered using the timesaving interpolation function.
So what exactly was altered? David's not going to divulge specific air-fuel ratios, but he says he added up to about 5 percent extra fuel in the top-end and slightly extra in the mid-range. Boost pressure could not be altered via the UniChip due to the Prado's lack of electronic boost control; its wastegate system is completely pneumatic.
Once tuning was complete, the UniChip module was cable-tied into position under the dashboard.
Modified Power Output
Again strapped to Turbo Tune's chassis dyno, the Prado showed a big response to the UniChip.
As seen here, the red plot indicates a highly impressive 19 percent extra power. Peak power is now 67kW ATW (up from 57kW standard) and torque is substantially improved across the entire rev range.
Closed Loop Running?
Unlike most EFI petrol cars, the UniChip interceptor affects both the heavy and light-load running of the Prado turbo diesel.
The Prado turbo diesel doesn't employ an oxygen sensor closed loop. That means there's no feedback system to correct the fuel mixtures dictated by the UniChip; all that's programmed into the UniChip takes full - permanent - effect.
What's the upshot? Well, there's the flexibility to tune for reduced light load fuel consumption, improved drivability and improved light throttle response (through revised static mixtures).
So how does the UniChip'd Prado now perform on the road?
Frank tells us there's a huge difference. "You don't have to kill it to get up hills anymore," he says. Engine smoothness feels unchanged, while overall fuel economy remains very similar to standard. More fuel is consumed only when the newfound power is being utilised.
In short, Frank is very happy with the results.
The Prado turbo diesel responds incredibly well to the fitment and thorough tuning of the UniChip interceptor. Every way you look at it, a 19 percent power gain for just under $1400 drive in-drive out is a bargain!
Beyond the extra power found through the UniChip, David suggests the next possible mods for the Prado include increased boost pressure and a high-flow exhaust. An upgrade intercooler would also be a good idea. With these mods, it's suggested another 15-or-so percent more power will be achieved.
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