Wasting the opposition has never been so easy!
I eased out from the curb, wary of the combination of a 390hp RB25DET engine and only RWD traction. With the superbly smooth engine already over four grand I fed power in gently: tyre destruction wasn't on the agenda.... An early up-change into second and with the revs at 2500, I nailed it.
In half a second the engine reached boost, the rear end danced slightly sideways with wheelspin and before I knew it, I was damn near the rev limiter. Wow. A snap change to third and boost rocketed up again - zip, the tacho swung around and there was a relentless urge forward as all the power was transferred to the bitumen. A glance down at the speedo and eeek! - it was time to slow down! Phew, exciting stuff!
For a single turbo engine that makes 390hp from only 2.5 litres, the RB25DET is one stupendously flexible engine.
All of the Nissan RB-series motors are beautifully smooth, well-mannered pieces of equipment but this one really proved the point. In standard configuration, only the rare Skyline GT-R engine (the twin turbo RB26DETT) is more responsive and powerful. Marginally behind the RB26 in max power, the RB25DET engine is a 2.5 litre, Double over head cam, EFI, Turbo engine which cranks out an impressive 187kW (250hp) in standard form.
The car that swallowed the mighty RB25DET is an Australian-built Holden Commodore, factory-fitted with the 3 litre single cam RB30 turbo Nissan engine. With a few tweaks, the standard turbo engine can be made to pull exceptionally well, but it was decided to swap in the RB25. Because they are from the same engine family, doing this is basically a bolt-in job. Over the RB30, the RB25 gives better economy, drivability and more power with the fewest possible mods.
Bought from a Japanese-import wrecker, the twin cam engine came without its wiring loom or computer. But since he was chasing considerably more power than stock, David (the car's owner) had already decided that a programmable aftermarket computer would be the way to go, anyway.
Before the engine was run on the dyno for tuning, Adelaide's Allan Engineering slipped Aries forged pistons into the bores to cope with the higher boost pressures that were expected. These retain the standard 8.8:1 CR to aid off-boost drivability. The only other mechanical performance modification was the fitment of an ATS high-flow turbo. This uses the combination of a Sierra T3 turbine wheel in an RB30ET exhaust housing, and a T4 compressor wheel on the induction side. While giving a superb top-end, the larger turbo means that the engine needs to be kept on the boil by careful use of the gearbox.
Intake air heated by the turbo travels through mandrel bent plumbing and is cooled by a front-mounted AVO air-to-air intercooler which performs satisfactorily - but David has plans to fit a monster 'cooler.
The afore mentioned engine management system is an Autronic SM2 unit which is programmed with maps for fuel, ignition and boost pressure. Specifically, it controls the engine's standard injectors, direct fire ignition (ie six coils) and the turbo's internal wastegate.
After thorough mapping on the engine dyno, a peak figure of 291kW (390hp) was achieved at 6000rpm (with boost limited to 14 psi). Low to middle rpm torque was also improved over the previous 3 litre turbo engine. However since boost doesn't creep over 9 psi until 5000rpm, the engine is extremely controllable and effectively 'fool proof'.
A deep, muted growl is emitted from the 3 inch mandrel bent exhaust which lets the engine breathe easily - the single Ultraflow muffler imposing minimal back pressure. Drop the throttle though and there's a distinctive whoosh from the exhaust as the turbine works hard at passing some serious cfm.
The previous engine's 5-speed manual is still in use behind the monster engine (it uses the same bellhousing bolt pattern) and has proven strong enough so far, but the standard clutch is getting a bit ragged. David refers to it as the standard 'slip-o-matic' clutch! The standard diff also remains in place with its 3.45:1 ratio and limited slip centre.
Without the Autronic system's traction control function yet in use, the sticky Falken 235/45 ZR tyres on 17 inch Antera rims can't cope with the king hit of power from the RB25 - but they sure lift the car's appearance. The vehicle also looks lower than it actually is thanks to the body kit's 'ground effects', but this is about the only part of the kit that David has original. Armed with plenty of experience, he's custom made his own front and rear bumpers, grille and fitted Cosworth bonnet vents to cool the engine bay.
Having owned the car for 5 years, David has had time to gradually built the car up into an excellent all-round package.
Thankfully, upgraded brakes haven't slipped his attention. On the Commodore they're 330mm vented, drilled and slotted DBA discs fitted on the front hubs, which are squeezed by AP CP5000 4-pot calipers with Endless carbon/copper pads. These calipers came as a bolt-on package that David says were dead-easy for him to put on. The rear brakes retain standard discs and Ultimate pads. The car stops spectacularly well.
Also keeping the projectile in control are Monroe gas shock absorbers combining with standard FE2 sports springs. This relatively soft suspension gives the desired ride quality, while Whiteline adjustable sway bars stop the car from leaning over dramatically. Whiteline adjustable top hats and a front camber kit also help to achieve optimum suspension geometry under all conditions.
Inside the cabin are the classy Calais door trims and seats plus all factory electrics. There's also a Momo leather steering wheel and gear knob, wood-grain dash fascia and an Alpine/ Pioneer sub-woofer sound system.
But according to David, it won't end there. He's considering fitting fibreglass guards, a bigger intercooler, roller bearing turbo, bigger injectors, 4 piston rear brakes, an interior re-trim and, and, and...
Just try stopping him!
Contacts:
Allan Engineering +61 8 8522 1901
ATS +61 8 8377 2511
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