There are few cars as iconic as the original Audi quattro. It arrived at a pivotal moment in the company's history and it's not a stretch to suggest that Audi's continued existence and its current remarkable health can be directly attributed to it.

Taking all-wheel drive out of the farmyard and giving it to the performance market was a stroke of genius. That it was fitted to a car with such a gloriously muscular appearance that went on to dominate the World Rally Championship didn't hurt either.

Its Audi five-cylinder turbo engine was another unique selling point and, before long, driving enthusiasts had embraced the quattro, granting it a special place in our collective imagination.

Nostalgia is a remarkably strong emotion and most of us already have the Audi quattro on our bucket list. We'll overlook its tendency to understeer and pretend they don't cost a small fortune to service and maintain. Yet their biggest problem is simply that it now represents 30 year-old technology. Even the rosiest spectacles can't overlook the improvements that have been made in efficiency, handling and construction during the intervening years, although we acknowledge that its age can also be its charm.

Somebody who fell under the Audi quattro's spell was Hank Iroz. The 29 year-old owner of Iroz Motorsport, located next to Las Vegas Speedway, wasn't even born when these cars first came to prominence, but that didn't impede him.

Owning a self-described "basket case" while in college, Hank had to learn quickly about maintenance for his 1981 coupe. He soon mastered the basics and began trying to make it faster. Before long, word spread among the owners of the 400 or so quattros left in the US, and the demand for his custom parts would pay his way through school.

Iroz Motorsport

Returning to Vegas two years ago, Hank's business plan was already mapped out, so he found a workshop and began specializing in fabricated and machined parts for the five-cylinder quattro, producing a range that includes intake and exhaust manifolds, engine mounts, etc. A lot of his Iroz Motorsport business is wholesale to other Audi tuners but the small team also services and tunes a range of VW/Audi vehicles, making good use of the in-house chassis dyno.

During our visit, there was a row of five-cylinder Audi models outside the workshop, and a number of quattros inside. We'd come to see the '83 quattro belonging to Sean McLane - a local man who also owns a Lancia Integrale, among other things.

Originally a 2.2-liter 10-valve model, Sean's coupe was in great condition. And while it formerly had a number of performance upgrades, it's now totally unique...

At some juncture, Hank learned that the quattro's 01E transmission could bolt to the TT RS 2.5-liter, five-cylinder turbocharged motor. This was interesting because the 2.5L is basically half the Lamborghini Gallardo's V10 - an engine capable of producing 550hp and revving to 8500rpm.

Compared to the Audi quattro's five-cylinder, the TT RS engine has a vastly superior head design with excellent flow characteristics. Hank reasoned it would be cheaper and easier to tune the 2.5L than the quattro's popular 20v motor, even allowing for the cost of the conversion kit. And being a relatively new powerplant, the 2.5L should be around for a while, helping to guarantee a plentiful supply of parts.

Even more interesting is that the Gallardo's V10 was also the basis of the EA855 (07K) 2.5L five-cylinder with multipoint injection used in the VW Rabbit and Jetta. In this guise, it's a rather feeble 170hp economy motor that doesn't have the benefit of direct injection. Yet it shares the same basic architecture as the Audi and Lambo versions, making it popular for VW turbo builds. What's more, it's incredibly cheap when compared to the Audi engine, allowing TT owners to rebuild damaged engines far more affordably once the rotating assembly has been strengthened with forged components.

After a brief discussion, Hank and Sean decided to install a 2.5-liter turbo motor into his '83 10v. An intense eight weeks of work saw the car ready for an event called "Battle Born quattro" last August. It's an annual gathering Sean organizes in Las Vegas, designed to tempt quattro owners out of hibernation and onto the racetrack.

In addition to the relative ease of tuning - a standalone ECU, big turbo, injectors and ancillaries saw 590hp - the 2.5L had all its timing chains mounted on the rear once it was fitted longitudinally into the quattro engine bay: it sat transversely in the TT RS, but the older car didn't have enough space to allow that...

The lighter, shorter engine saves 65 lb over the quattro 20v motor, putting less weight over the long nose, helping to improve weight distribution and handling. Using a VW block, it was dressed for battle with forged Mahle pistons, rods and a TT RS forged crank. The compression ratio is a relatively high 9.5:1 because the engine runs on E85 ethanol to maximize output. With a custom flywheel and clutch, the engine and transmission were united, but the oil pan fouled on the sway bar and crossmember. So Iroz Motorsport fabricated a baffled pan with seven-quart capacity to allow sufficient clearance.

The oil filter needed to be remotely mounted to gain more space, now residing in the driver's side fender. The engine could then be lowered onto the custom Iroz mounts.

For the exhaust, the company used its own equal-length headers, incorporating a Tial blow-off valve and V-band connector. It has matching stainless steel downpipes that were V-banded to an aluminum exhaust system. The latter helped reduce weight, gave a pleasing exhaust note and, we have to say, looked tough sitting in the S1-replica rear bumper.

The turbocharger is a Forced Performance HTA 3582R. It's based on the Garrett GT35R but uses a billet compressor wheel for strength at high boost. It develops most of its power from 4000-7500rpm and, while Hank admitted he could have gone bigger to produce more power, Sean liked its drivability.

Rather than run everything on the quattro's original electronics, Iroz Motorsport installed a VEMS V3 standalone ECU that allowed them to tune for the E85 fuel. Hank has worked with this system before and likes both its flexibility as well as the Bluetooth functionality. It can be mated to any Android device, so the Audi has a tablet mounted in the center console that monitors every engine parameter, from boost to fuel pressure, and can even provide touchscreen navigation, etc.

With a thirst for E85, a MagnaFuel ProStar 750 mechanical pump was fitted, along with huge injectors to supply sufficient fuel for the high horsepower application.

With the hood open, you can't help but admire the custom Iroz intake manifold and billet cam cover. These were retro touches requested by Sean as a tribute to the car's roots. In fact, Hank told us the intake is a rally-style dual-plenum design that was popular in the '80s but is no longer necessary with modern software. Yet it looks marvelous with "Turbo" engraved in the original font.

Out of sight is a custom intercooler and radiator, stacked in the nose with end tanks fabricated using the in-house CNC machine.

So how much power does it produce? On the Iroz dyno, the coupe put down 586hp at all four wheels, with 530 lb-ft of torque. Assuming a conventional 25% transmission loss, this 1983 Audi quattro has about 740hp at the crank at 28psi. However, this represents a relatively early state of tune, with Iroz aiming for 600awhp and 650 lb-ft at 35psi with software revisions.

As it stands, the car is frighteningly fast, as can be witnessed in our online video alongside the TT RS that can be found at www.europeancarweb.com

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