Last summer I took delivery of a five-year old BMW M135i. A three-door with a manual gearbox. It had covered a little under 30,000 miles and cost £17,500 (you can pick up leggier cars today from £14,000). Over the following eight months we modified it step-by-step to see if we could make a better car out of an already pretty good one. If you've been following the reports here you'll know the score. Working with Birds, the BMW specialist that's been tuning and servicing Bavaria's finest for longer than I've been alive, we've uprated the suspension, fitted a Quaife limited-slip differential and remapped the engine to liberate more power and torque.
What we never consciously set out to do was build an alternative to the M2. But with the project now complete and the total bill standing at £24,000, I couldn't resist the comparison. For close to half the price, have we built something that merits comparison with BMW's baby M-car? On looks alone, no we haven't. The M2 makes the M135i look weedy and undernourished. But on pure performance terms, yes we have. In fact, our M135i is actually quicker than a stock M2.
Next, we fitted a Quaife LSD, added a short-shift kit and modified the clutch pedal to have a weightier action. Finally, with the car handling the way we wanted it to, we remapped the engine to 395hp and 420lb ft. The full B1 upgrade package, as Birds calls it, costs £6,643, which includes fitting, VAT and a two year warranty. You can check back through the previous reports if you're after a fuller description of each modification.
Incidentally, the upgrades can be made individually. They also fit the M235i coupe, too, as well as the later models, the M140i and the M240i. (You may remember we had decided to upgrade the brakes as well. Unfortunately, the supplier wasn't able to deliver the parts in time).
From there it's punch and counterpunch. The M135i has better damping pliancy over bumpy, uneven roads. You feel the suspension working hard to allow each wheel to rise and fall with the road and keep the tyres pressed firmly into the surface, which gives you huge amounts of confidence. By comparison the M2 skips along a little, although this particular car is better in that respect than any other M2 I've driven. The M2 has its much wider tracks, though, and you sense the car's greater poise and stability in every turn, and appreciate its more positive steering.
During my 9,000 miles or so with the M135i it never missed a beat and hasn't cost a penny to run beyond normal servicing. Oh, apart from the £360 I had to spend to get a particularly nasty three-panel key mark repaired. It averaged a little over 30mpg, which isn't at all bad given the performance it's capable of. Regrets? Only one. I wish we had started with the much better looking, slightly more expensive M235i.
Car: 2012 BMW M135i
On fleet since: July 2017
Mileage: 38,650 (delivered on 29,800)
List price new: £29,995 in 2012. Bought for £17,500.
Last month at a glance: Tricked-up M135i holds its own against M2
Upgrades (all prices fitted, including VAT)
Bilstein suspension upgrade - £1,865
Quaife LSD - £2,033
Short-shift kit - £532
Clutch pedal modification - £113
Engine management upgrade - £2,700
Cost of full B1 kit - £6,643
'You could get an M135i for that' - so we have!
Shockingly good improvement with new suspension fitted
Dan gets a dose of LSD and loves the effects
How far does power actually corrupt, then?
[Photos: Stan Papior]