Rumour has it the 335i should have worn an M3 badge, but V8 shoehornery from the likes of Audi and its RS4, along with Mercedes and its C63, led to BMW choosing a naturally-aspirated V8 for the E9X M3. This engine was labelled the S65; it produced 420bhp and despite the E30, E36 and E46 M3 having only been subject to four-cylinders for the advent of the M3, and six-cylinder power from then on, a V8 was more associated with the E39 M5. However, its appeal was still hard to resist, even if it did momentarily poke M3 purists in the eyes...


BMW 335i E92 tuning and buying guide

Of course, the 335i being the M3 that never was is just a rumour, but further evidence does lie within BMWs more recent focus on turbocharged engines. Take the F10 M5, a 550bhp twin-turbo V8, and the imminent F82 M3 ( BMW F30 series renamed model), will have, yes you guessed it, a twin-turbo straight-six, a la the 335i. The 3-Series V8 fling is over.

At the time of development, BMW could build tremendous naturally-aspirated straight-sixes in its sleep, but the 335i’s N54 was the first turbocharged petrol engine since the iconic 2002 Turbo. So making a meal of it would have been something of an embarrassment.

It got rave reviews, with the press applauding its lag-free 302bhp, 295lb/ ft torque power delivery and effortless overtaking capabilities, but in 2010 one turbo was dropped and the engine was renamed the N55. We feared the worse.

However, power and torque figures remained the same but astonishingly, the 295lb/ft was delivered even earlier.

I road tested one in the November 2010 issue and the ‘TwinPower Turbo' cam cover writing was obviously a way to satisfy those who felt deprived of the N54's additional blower. It proved to be just as impressive though, even if the older BMW N54 is reputed to be more receptive to engine tuning. The move to a single turbo buoyed fuel economy but perhaps BMW thought its future M-car range needed to be distinguished by its twin-turbos.

Naturally, the 335i by model name alone didn’t have the credentials to stand on the M3’s toes, so the production version was watered down to 302bhp, way behind the yet to be released E92 M3, with its 414/bhp. Similarly, back in the 'nineties the E36 328i was strangled by a 320i inlet manifold which pegged it back to 192bhp, no more than a 325i. Look to the 3.0-litre E36 M3 though, and that was producing 286bhp. On paper, stark differences between regular models and anything beginning with an ‘M’ have to remain paramount.

The 335i may have been around since 2006, but 302bhp isn't a figure to be dismissed in 2012. and in reality this is actually a modest yield for a twin-turbo 3.0-litre straight-six - take it as a hint of its true potential. Naturally aspirated engines have always been notoriously expensive and labour intensive to tune because reaping serious gains calls for uprated internals. Forced induction engines on the other hand can offer far more bang per buck.

This is what has led to many a 335i following the seemingly faster M3 only to remain fixated in the rear view when M attempts evasion. The reason? Usually a remap, which brings a 335i to nigh-on the M3’s 400-odd power output. However, even in factory trim the 335i has more accessible real world performance because having driven both, an E9X M3 doesn’t properly loosen up until a high rev count, which is where it needs to stay in order to shake off a 335i.

Compare the power delivery in the M3's BMW S65 against the 335i’s N54’s nature, and the latter will provide lots of lowdown shove thanks to the turbos, or later single turbo - both variants show minimal signs of lag. This means performance is unearthed at an early stage. This instant access is perfectly suited to road use which is mostly a strictly governed environment which rarely permits downshifts and a clip of the redline, to unleash an engine's reserves. In short, in a 335i you get to enjoy what's on tap more of the time.

However, a remap alone doesn’t unlock the door to the performance perks of an M3 - the 335i needs improvement in other areas first. Not that we're dubbing this as a breaking news story, but with 335i values now under £10k it 's possible buy and create a fast road M3 contender for less than £15k. We show you what to spend your hard earned on...


Wheels & tyres

First up, forget about the run flat tyres. If they are coming up for renewal, the steep replacement costs aren’t worth the lack of performance you get in return. According to Kevin Bird of Birds UK, for road use the E9X favours Continental Sport Contact 3 or 5P tyres, which offer excellent grip in wet conditions. As Drive-My discovered when we drove on the Sport Contact 3 at test facility, MIRA, around its wet handling course.

If you use a 335i on track, there are alternative tyres that may offer better dry grip over the Continentals, but with the deluge the UK receives, the latter may offer the best solution. Wheel choice is endless but consider that an 18-inch diameter offers improved handling, while 19-inch wheels are arguably more of a visual treat so long as you strike with the correct offset.


Differential

When we drove the BMW Performance version of the 335i, it was a very impressive package but a lack of LSD blew a large hole in its armour. A chink that has to be filled by a keen 335i driver. If you don't find the 335i lacking in traction then you probably won't benefit from the expenditure needed to install the likes of a Ouaife ATB differential.

Birds charges £1,225.00 phis VAT to supply and fit a Quaife. which comes with a lifetime guarantee. Post-February 2007 manual 335is have a welded crownwheel so there is a premium of up to £470 plus VAT. According to Birds, stepping away from the run flats and opting for a Ouaife unit dramatically changes the characteristics of a 335i.


Suspension

While an engine benefits from products and tweaks that prove their worth on a rolling road through increased power and torque figures, suspension is something that sparks great debate because, lap times aside, it's largely subjective. It's the thing that leaves race teams scratching their heads because there are just so many parameters which are open to adjustment, often leading to a negative outcome.

This guide isn’t aimed at a 335i destined for circuit racing, more for road use with the occasional track  day. From the factory, in order to put a gag on body roll, the spring rate was upped which in turn imposed on ride quality. The standard rear anti-roll bar diameter is a diminutive 14mm, as a beefier one would have reduced traction, thereby highlighting the shortfalls of an open diff.

Ideally the anti-roll bar should be addressed when a LSD is installed. One budget solution is to source an E93 M3 rear anti-roll bar or alternatively, Eibach supply uprated versions and the likes of Birds supply Hartge uprated bars. The front anti-roll bar isn't such an issue and the upgraded diameter for this is only a couple of millimetres.

Now it's time to focus on changing the factory springs and dampers. The aftermarket choices are endless and you may already have a preferred brand or setup.

For a complete solution, Birds has developed a kit in conjunction with a renowned handling and suspension consultant, whose findings were translated to big industry names, Eibach and Bilstein. The result is a custom (non adjustable) damper and spring setup that's only available through Birds. It's not cheap at £1,316.00 plus VAT installed, but if you are looking for a kit designed specifically for the debacle we call UK road surfaces', this would undoubtedly be a preferred choice.


BUYING

Jason Barker runs the sales arm of Birds and he is well accustomed with the 335i. Despite the rumour mill generating some negative reports on turbo failures, the N54/N55 is actually considered reliable, but oil and filter changes are essential to the turbo's longevity - avoid extended service intervals at all costs.

Wear and tear items are similar to any other E9X, but 335i problems include the high-pressure fuel pump, fuel injectors and coil packs. Jason’s 20 years in the business has also developed a keen eye for previous accident damage. 'They are fast cars so some have been damaged but they do sell well, especially in this economic climate." By this he's referring to owners of M cars who are settling for something that still performs, albeit with more affordable running costs. Consumables such as 335i brake discs for example cost much less than the equivalent M3 items.

Whether you opt for manual or DCT is entirely down to personal preference. Both transmissions have proven reliable and city dwellers may prefer the use of Drive, with 'manual' mode when the time is right. However, as technically engaging as this may be on paper, and utterly clockwork in its operation, it still dislodges a major part of the driving experience. If you have gone to town on making a 335i more of a driver’s car, then the conventional six-speed manual is a clear winner.

Values can kick off from as little as £8,000. but more commonly most 335is command at least £9,000. For this amount you will be buying into an early 2006 (56-reg) example with around 90.000 miles. Extending your budget to £10,000 will procure lower mileage examples of the same year but £11,000 onwards seems to be the golden figure tor low mileage 335is. At the time of writing, we found a manual BMW E92 with full service history and 52,000 miles for just £11,000 on a forecourt.

Don't have the budget for this just yet? Every 335i, barring the Touring, has M Sport dampers from the factory which work just fine with Birds' Eibach springs. They are available independent of the package for £574 plus VAT fitted. For this outlay expect an improvement in ride quality and better adhesion when pushing-on over unsettling routes. Balance on the limit will be much improved.

There are other solutions out there that will stiffen a 335i up further, but for road use it's important to have compliance. Make this paramount if yon want to enjoy your 335i to the full.


BIRDS BMW 335i

Birds' E92 335i demonstrator is a 2006 430bhp DCT-equipped twin-turbo which sports most of the upgrades discussed in this feature. ‘It’s a fantastic GT car. It’s not too big and feels close to the old BMW 635 CSi E24.

To do long, fast distances in it’s completely effortless, which is probably the definition of a good GT car. We looked at buying a 1-Series E8x generation at the same time, but some cars hit the right spot and if you are lucky enough to hit it at a good time then it goes really well. Just like we did with the E30 325i in the mid ’eighties. we carried out the changes when the 335i was still a new car.’


Brakes

The standard brakes won't come as a disappointment for road use but if you do plan on making an upgrade. Birds suggests holding out until you have enough saved for a complete kit, as that will offer a vast improvement over merely replacing the standard friction material. Companies such as AP Racing provide complete caliper and disc upgrades that will really make a 335i stop.


Engine

Why is this last on the list? Well, it's become clear that money is better spent in other areas first. Once you are happy with the way your 335i rides, handles and grips, there's a 3.0-litre twin-turbo ready to be dabbled with. The later single turbo N55 isn't to be ignored but the N54 provides a better platform.

Extracting 400 reliable bhp is possible just from a remap but Birds regards 360-370bhp to be the sweet spot of the chassis for road purposes. Although 400bhp will satisfy most requirements it can get expensive if you want to push the boundaries further. It also places a question mark over how much you will be able to enjoy the 335i without booking a track day.

Birds' 335i demonstrator, which was photographed for this feature, produces 430bhp and they found the standard intercooler operated effectively on the road, if not better than some of the huge aftermarket versions which dissipate heat at a slower rate as they are effectively a heat vessel.

Winding the boost up further can be avoided by a change to aftermarket cats - a 200-cell per inch setup is ideal. These will give an immediate increase in power and torque throughout the rev range as the exhaust gases are dispersed at a much quicker rate. The downside is that the engine r check light may come on after a year or 15,000 miles of use, but fitting a lambda simulator tricks the management into thinking the cats are running at full efficiency. Alternatively, diagnostic software can disable this warning. Furthermore, a good quality aftermarket exhaust system will assist in reducing the back pressure.

The N54's turbochargers can also be modified. The exhaust turbines are ‘clipped’ to open up the gaps between each blade. This increase, along with a bigger compressor, helps to disperse gases but in exchange a small portion of the lowdown torque will be lost due to a swell in turbo lag. The upshot will be 30bhp at the top end, but expect to pay £1,500 on an exchange basis.


Verdict

There’s no need to scoop this guide up with two hands and improve every department. In an ideal world maybe, but picking and choosing different elements of the subjects we have covered will put a fresh slant on the 335i driving experience. A simple remap will put one alongside an M3 on a straight piece of road. Or perhaps you are content with 302bhp but yearn for better traction, in which case a LSD followed by suspension changes would be more suited.

If we had to take three products from this feature and fit them to a 335i, Total BMW's shopping list would consist of an uprated rear anti-roll bar, a set of Birds-developed Eibach springs and a Quaife, or similar, LSD. In our eyes these choices are an introduction to exploiting the 335i for what it’s really worth. The M3 that never was? Now that's a question mark that continues to cast its shadow.


Above: Don't discard the standard intercooler-only opt tor a proven aftermarket version.

Right: Get rid of the run flat tyres and fit conventional rubber. Birds runs a wider 245 section at the front and 275 at the rear.

Below: The later N55 used clever wording to excuse the previous twin-turbo setup.

Below: 19-inch wheels benefit aesthetics, but 18s remain the driver's choice.

Right: Start with aftermarket cats to help disperse exhaust gases and then replace the factory exhaust system.

Below: Standard brakes will suffice for road use but track- bound 3351s will profit from an upgrade such as an AP Racing Formula brake kit.

Above: The 335i offers respectable fuel economy and a 302bhp blown straight-six. What’s not lo like?