BMW 3-Series

Richard Meaden
23 May 2007

Performance upgrades from German tuner Hartge create BMW M3 rival from base 335i

Evo Rating: 
(conversion) £15,890 inc VAT and fitting
Big performance, superb chassis
Pushes 335i’s price to £50K

When a tuning company decides to play with a car that’s essentially excellent, there’s a very real danger that the core qualities that made the standard car so good will be sacrificed for the sake of extreme power outputs and a super-size alloys. So you can imagine our scepticism when the evo car park resonated to the deep-chested rumble of the new Hartge S3-3.5.

Nothing against Hartge, you understand. Indeed, from experience we know it creates some of the most thoroughly considered conversions in the industry. And yet, knowing how silky and understatedly stonking the biturbo BMW 335i it is based upon is, we couldn’t help but wonder what this re-interpretation would be like.

There’s no doubting that Hartge’s 335i looks the part, a set of 20in multi-spoke ‘Classic 2’ rims, low-profile Pirelli P Zero Nero rubber (235/35 front, 265/30 rear), a discreet carbon chin spoiler and a quartet of polished tailpipes seemingly all that’s required to transform the standard 335’s looks from plain to plain stunning.

However, it’s beneath the svelte two-door body that Hartge has really gone to town. As tested, the S3-3.5 currently develops 360bhp and 328lb ft, thanks to a re-map of the motor’s ECU. The engine work is still in the final stages of development, though, and will eventually run sports catalysts and possibly an intercooler, lifting power and torque outputs to 381bhp and 336lb ft – a thumping gain of 79bhp and 41lb ft over the standard 335i.

Impressive figures, but what they fail to convey is the increased sense of muscle and urgency, and the delicious and seemingly ever-increasing surge of power and torque as you power through each gear. In developing the revised management system, Hartge found just how much BMW had reined-in the 335’s engine (presumably to avoid any embarrassing comparisons with the E46 M3), but now that the engine has been allowed a little more electronic freedom it delivers big league performance without any compromise in smoothness.

The S3-3.5’s chassis is a comprehensive reworking of the standard car’s, with new springs, gas dampers and anti-roll bars. Aimed at dialling-out the 335’s inbuilt understeer and comfort-biased settings, the new suspension is firmer than standard, especially in rebound, while the new anti-roll bars give the S3-3.5 a much more alert feel without making the turn-in too sharp or the transition from grip to slip too abrupt. Given the extreme tyre sizes, the fact that this added dynamism has been achieved while retaining a supple and well-controlled low- and high-speed ride is impressive and results in very satisfying progress on all manner of roads.

Perhaps the most frustrating flaw in the standard 335i is its lack of a limited-slip differential, for it makes the on-limit behaviour inconsistent and less entertaining than it should be. Hartge has remedied this by fitting a Quaife diff with a 70 per cent bias ratio. Not only does this help the S3-3.5 put its increased power and torque onto the tarmac with less likelihood of triggering the traction control system, but when you disengage the electronic safety net it allows you to bring the tail into play with the most minutely adjustable precision. It even makes the E46 M3 – complete with M differential don’t forget – feel like it lacks control.

The boys at Hartge have also improved upon that traditional BMW blind spot, brakes, electing to fit a set of 356mm AP Racing front discs and six-pot alloy callipers to the S3-3.5, endowing it with brake feel and performance an M3 driver would die for.

Perhaps the biggest compliment we can pay the S3-3.5 is that it feels so cohesive. No one element of the conversion dominates the experience, and it’s so well rounded you get the distinct impression that if BMW’s M Division had opted to develop the 335i’s biturbo six instead of going down the high-revving naturally aspirated V8 route for the new M3, the S3-3.5 is what they would have arrived at.


Engine In-line 6-cyl, 2979cc, 24v, biturbo
Max power 381bhp @ 6000rpm
Max torque 336lb ft @ 5500rpm
0-60 4.9sec (est)
Top speed 175mph (est)
On sale Now

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