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Compact with Compressor

A neat E46 BMW 325ti Compact with one of Australia's only Infinitas SK supercharger systems

Words by Michael Knowling, Pix by Julian Edgar

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At a glance...

  • At a Glance:
  • 2002 BMW 325ti
  • Infinitas SK Stage One blower kit
  • M3 paddle shift
  • M3/GT3 brakes
  • Imported high-flow exhaust and body kit
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When you line up at the lights next to a BMW it’s always wise to first look at the badges on the boot lid. If you can see the letter M you’d better be careful – M3, M5 and M Coupes have the grunt to well and truly ruin your day. But numbers like 316, 320 and – to a lesser extent – 325s are pretty easy prey. You can dump the clutch with confidence.

But beware of this 325ti owned by Sydneysider Michael Fitchman.

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This compact Beemer maintains a classy, smooth look and there’s nothing to hint to its performance. It's quiet, it idles smoothly and everything seems fairly sedate. But when Michael flicks his way up through the gears using the M3-style paddle shifters, you’d better be prepared to be dealt a blow from its imported supercharger kit. BMW badge theory goes down the toilet...

This 2002 E46 BMW 325ti was purchased second-hand by Michael a couple of years ago after he was impressed with the style and finish of his previous 733i. The ti provides that same satisfaction of ownership but Michael felt that the 2.5-litre engine could do with a little more poke. And here enters Bavariacars Motorsport.

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Herbert Gattermeier of Bavariacars suggested the fitment of an Infinitas SK Stage One supercharger kit – one of the first in the country. So what on earth is the Infinitas SK supercharger kit? Well, at the heart of the system is a compact and quiet ASA TM1-12 centrifugal supercharger which is mounted on a CNC-machined aluminium bracket. The kit also comprises all necessary pulleys and belts and, interestingly, the ASA blower must be integrated into the engine’s lubrication system using a T-piece at the oil pressure sensor and a return fitting in the sump. The compressor draws air through a K&N pod filter.

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In the entry-level SK Plus kit you don’t get any form of charge-air cooling but in the Stage One kit (as chosen by Michael) you receive a 12-row air-to-air intercooler that nestles into the nose without any cutting or grinding. The core has been painted matt black to ensure a stealth installation. The intercooler plumbing is TIG welded stainless steel equipped with twin Bosch blow-off valves and maximum boost pressure is a conservative 0.4 Bar (6 psi).

Erik Gattermeier from Bavariacars recalls that the standard 325ti maintained a stoichiometric air-fuel ratio at WOT to about 5000 rpm, at which point it richened into around 12.5:1. By installing the supplied ASAtronic controller (which modifies the airflow meter output) and a new fuel pressure regulator with modified lines, the car now holds stoichiometric to around 5000 rpm and richens to 11.8:1 near full power. The injectors and fuel pump remain standard.

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With the off-the-shelf blower kit fitted and tuned, Michael’s 325ti was elevated from its standard output of 101kW at the wheels to 161kW at the wheels (a gain of 59 percent). Infinitas claims 199kW at the flywheel along with 320Nm of torque. In addition, Michael has recently added an Eisenmann high-flow exhaust which has been modified for extra noise suppression. The new exhaust should theoretically release around 10kW for a total output just over 200kW. (Incidentally, the Stage 2 Infinitas SK blower kit comes with an upgrade exhaust, slightly more boost and accompanying tuning changes to deliver a claimed 213kW.)

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The supercharger gave the 325ti a much greater power output but there were a couple of other mods necessary to help make this newfound extra grunt more accessible in normal driving. First, the standard diff ratio was shortened from 3.25 to 3.46:1 to sharpen response without causing excessively high cruise rpm on the highway. We’re told that a limited selection of compatible diff centres prevented employing an even shorter ratio. The next step was the fitment of a US-sourced M3-style paddle shift system which integrates with the standard Steptronic transmission and wiring loom. A M3 steering wheel is also included as part of the upgrade. The paddle shift system makes it much easier to drop the engine back a ratio or two and bring the engine onto boost.

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Braking performance has been massively boosted using E46 M3 discs teamed with Porsche GT3 4-pot calipers mounted on custom machined brackets. Braided stainless steel brake lines are also included.

Subtle styling changes distinguish Michael 325ti from other examples. A Rieger body kit gives a M3-like appearance thanks to front and rear bumper extensions and side skirts. The standard wheels are also replaced by 17 inch BBS jobs wearing Continental tyres. These give extra grip while an aluminium tower brace improves front-end rigidity. The M3 steering wheel and paddle gear shifter is the only change to the standard leather-lined 325ti cabin.

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This is one of Bavariacar’s first experiences with the Infinitas blower system and they’ve come away impressed by the quality construction, ease of fitment and performance. Herbert Gattermeier says the car now offers straight-line performance that feels similar to the expensive M3 (which is slightly heavier than the 325ti). At present, Michael has no further plans for modification as there are some concerns regarding the strength of the transmission. But if the transmission were to fail Michael wouldn’t be too disappointed – he’d probably switch to a high-strength manual gearbox and pursue even more power.

But we don’t think that’d be fair without some reorganisation of the numbers on the boot lid!

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