NSX In Excess

Honda's randy looking NSX can only be called a SuperCar. In standard form its 3.2 litre all-alloy V6 punches out 206kW and the sophisticated suspension and mid-mount engine design fits the traditional sports car formula perfectly. But slip a couple of turbos between the rear wheels and a SuperCar just got super-er! No longer does it compete in the Supra RZ category; it's now hot on the heels of Marranello's finest.

Cameron Parsons is the man lucky enough to hold the keys to this technological masterpiece - a machine which has had more than its fair share of enhancement. With the intention of going competition racing, he imported this 1991 NSX directly from Japan - enabling the car to be his for about half the price of an Australian-delivered example. The only catch is, the car can't be legally driven on public roads - it's 'race only'. This isn't really a problem though, because that's exactly what it has been set up for - pure, unadulterated white-knuckle road-racing!

And that's where Australia's Advanced Vehicle Operations (AVO) steps into the limelight. Initially, they twin turbo'd the car using the standard engine internals and low boost pressure, but the simple seduction of tuning up the boost soon saw the limits of the standard pistons...

Then it was time to get serious. Presented with the task of getting around 550hp, AVO responded with a bullet-proof engine build and one of the most well engineered 'one-offs' we've ever seen. The Honda V6 has been split open and re-built with a set of American-sourced forged pistons that provide a more turbo-friendly compression ratio of 9.1:1 - down from the factory's 10.2:1. The bottom-end remains near standard, keeping Honda's factory titanium rods but with specially made ARP rod bolts. Terry Wilson of AVO enthused about the strength and design features of the Honda engine, saying it's incredibly well balanced and uses such features as main bearing girdle strengthening all ex-factory.

While the heads were off, they received some minor cleaning up before being filled with Competition Cams stiffer valve springs. Stock camshaft profiles were kept to maintain the engine's amazing driveability. The other changes made to engine mechanicals include a 7 Bar (100psi) high-volume oil pump and a modified water-cooling system with custom header tanks.

Fabricating a pair of exhaust manifolds was an exercise in compact packaging. These labour intensive custom three-into-one tubular headers channel gases into the turbines, while short length twin 3 inch pipes and an AVO muffler are used post-turbo. Each of the Garrett-based '320hp' ball-bearing turbos delivers around 10psi boost into individual AVO air-to-air intercoolers, mounted proud behind the custom Lexan rear window. Getting air to flow through the cores took some ingenuity - you can't just stick them out the front when you've got a mid-engined car (not without 3 miles of plumbing anyway!).

AVO used the air intakes on the side flanks of the NSX to feed a pair of large diameter ducts that snake their way up to the cores. To get the hot air out, a custom-fluted Lexan rear window had to be made up, which took a quite few after-hours nights! All turbo plumbing has been sent off for a ceramic coating to insulate against heat. The end result is a maximum intake temperature of around 55°C on sustained full boost...

Fuel and spark come courtesy of the Honda ECU, which has been augmented with an in-house AVO extra injector driver and six extra injectors mounted one near each intake port. This system works very well and the engine also benefits slightly from the cooling effect of the fuel being injected into the intake runners. The engine dines on a minimum fuel grade of premium unleaded, but will be seeing Elf race fuel very soon - we'll let you know why later! Because the standard ECU remains in place, the stock rev limit is still imposed at around 8000rpm - it's the turbo-torque which enables the big hp numbers to be produced.

Backing the alloy V6 is the standard NSX 5-speed manual gearbox. It's been filled with stronger NSX-R gears plus a 40% higher clamping force pressure plate with a twin plate clutch. The factory limited slip diff copped a reworking too, with AVO strengthening and modified it to nearly the lock-up stage.

Racetrack ready, the 1200-odd kg car is now suspended by fully adjustable Mugen front and rear dampers and Mugen springs. Stock anti-roll bars are still fitted. The car's handling is just mind-blowing. Turn-in is crisp and precise and the car's exit attitude can be easily throttle controlled with the hit of around 550hp! With the car's estimated 320km/h terminal speed, the braking department was brought up to spec with pizza-dish sized 13.5 inch Brembos with four-pot squeezers. Cameron says there's absolutely no fade and the overall braking performance is totally unlike any other car he's been in.