Subaru WRX STI 22b or a house? You'll need seriously deep pockets if you want to snag this ultimate Mitsubishi Lancer EVO rival

An example of one of the rarest Subarus produced, the WRX STI 22b, is headed for auction next week, but you'll need some very deep pockets if you want to park this one on your driveway.

Set to go under the hammer at Collecting Cars Australia, this 1998 example is one of only 425 cars produced worldwide (number 258), and is expected to nudge the $500,000 mark.

With 71,000km on the odometer, the 22b up for grabs is certainly not in showroom condition, but is still expected to fetch much more than the $360,000 minimum these models have fetched in the past at Collecting Cars Australia.

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However, those after an unmodified example might be disappointed to see various components have been replaced.

From the photos of the engine bay, it's clear a lot of work has been done with some notable changes including a new intake and battery relocation.

The interior has also been tweaked with an aftermarket single-din head unit, the addition of extra gauges and more, while a new exhaust with a titanium tip can also be glimpsed in the photos.

This indicates some serious work has been put into this 22b, but a fully detailed modification list, and power and torque outputs, are yet to be revealed.

Arguably the ultimate Subaru, what differentiates the 22b from a more common WRX STI of the same era is its coupe body style, as well widened wheelarches that are filled with 17-inch BBS wheels.

The centrepiece of the 22b however, is its larger displacement, hand-built 2.2-litre turbo-petrol four-cylinder boxer engine (hence the name), up from the WRX STI's 2.0-litre unit.

Though power – on paper – is the same 206kW from factory when compared with a standard WRX STI of the same vintage (thanks to Japan's gentlemen's agreement to not advertise sports cars with more), torque climbs from 353Nm to 363Nm.

Of course, drive in the 22b is sent to all four wheels via a five-speed manual gearbox.

This particular 22b calls Queensland home for now and is not one of the five Australian delivered cars (having been imported from Japan), but goes on sale from Friday, June 9.