You may remember a recent video in which Autocar’s special correspondent Mauro Calo and I asked each other: what is BMW’s greatest M car? You may also remember that we decided the closest to it was the E46 M3 CSL. If we were creating the ‘perfect’ M, it was the car we’d take most elements from.

It has an astonishing engine – of all BMW motors I’ve tried, second only to the McLaren F1’s. It has a great, familiar, front-engine, rear-drive balance and a sense of real urgency about it. And it’s about the ‘right’ sort of speed and size.

One thing we wouldn’t have is the standard ‘SMG’ (sequential manual gearbox) transmission. There are lots of good two-pedal transmissions: either torque converters that hook up quickly or dual-clutch alternatives. The SMG is neither.

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It’s a regular manual with a robotised shifter and clutch. And there’s about one gearchange in 50 – when you’re flat out and you want a quick, brutal upshift – when it’s satisfying. The rest of the time it shuffles and pauses or bangs and irritates. Some owners swear by it, but for me it almost spoils the car.

Step forward David, by day a validation engineer for a big British car company, by night the owner of one of the 422 right-hand-drive CSLs.

Being an engineer, David, alongside a friend at Everything M3s of Banbury, spent weeks preparing what he’d need to give his CSL a manual gearshift. I settled in expecting an extended build blog. And then over a long weekend it was finished.

Everything bolts into place, David told me last week. You can even extend the pedal box, though fitting a new one is easier. The bell housing needs a modification, but swapping it is more straightforward. And this is, after all, a 3 Series built on a line in quick time: there are perforations in foam already, holes that just need grommets removing, and you buy all original BMW bits from BMW to make the transformation. The sketchiest part is drilling out rivets to remove where the gearlever pokes through, but even if you change your mind, a new panel costs £12 and you could reverse the process back to being an SMG in a weekend.

Having tried this car, I wouldn’t: a manual CSL is a CSL unleashed. It’s more analogue, each gearshift is the one you want to make and engine and gearbox get along just fine.

The conversion feels like BMW made it this way. And made it better.