Turbo Technique

The Citroen BX wasn’t the first turbo diesel that people could buy, even in its class (the Volkswagen Golf got there first) but it is in my view the best. Citroen had a long history of producing diesels – right back to the 1930s with British Ricardo Engineering involvement.

Ricardo helped design the pre-ignition chamber that is a feature of most indirect injection diesel engines. They’re called indirect because the injector actually fires in this small chamber rather than directly into the cylinder itself. Ricardo’s trick improved the swirl characteristics of the burn and improved both efficiency and refinement. That same technique was employed on the XUD, which was launched almost 50 years after the first Citroen diesel.

The XUD actually first saw use in the Peugeot 305 and Talbot Horizon – Peugeot by then owned Citroen and Talbot. The engine was soon featured in the popular 205 as well and gained popularity, especially in France. Diesel options were by no means common on family cars at this stage but the XUD wasn’t just a ground-breaker for being a diesel, it was also quite revvy, reasonably powerful and smooth in use. It was most unlike other diesel engines. Sure, it still clattered a great deal when starting from cold, but on the move, it was smooth and almost refined.

At this stage, you couldn’t buy one with a turbocharger, but that changed in 1987 when the Citroen BX gained a blown option, most commonly seen here as the DTR Turbo. Citroen already had a turbo diesel on the market in the form of the CX, but the BX was much more afforable.

The BX range was tweaked later to include the TZD Turbo, which was effectively a GTi with a turbo diesel engine. A sporty bodykit helped prove that diesels were no longer slow and cumbersome. They could be fun!

The BX could dash to 60mph in less than 12 seconds and top 110mph, but the mighty 134lb ft of torque at a mere 2100rpm meant in-gear acceleration was the real talking point. The 50-70mph dash – so critical for overtaking – took a mere 11.6 seconds in top gear. That’s quicker than a Mk1 Vauxhall Astra GTE. This was proper shoved-back-in-your-seat acceleration from a car then capable of topping 40mpg very easily.

Sounds brilliant, but how is it translating in every day use? Well, I’m not yet really sure. Going from the simple, flat-but-feeble torque curve of the normally aspirated diesel really is a massive change. In that, you just got up to fifth gear and stayed there pretty much all day. There was no point going to a lower ratio for more power as the engine simply didn’t have any. It was rather unusual because once wound up, you could travel remarkably briskly with the engine doing no more than 3000rpm. An odd experience!

BX Turbo diesel

Turbo Technique. Exhilarating but hard work

The turbo diesel isn’t like that. One reason is taller gearing, which makes motorway travel much more relaxing. The downside is that fifth gear is no good below about 45mph, so you have to downchange more often. You also have to downchange to try and keep the engine on boost. Below 2000rpm, it’s just like there’s no turbo at all. The urge suddenly kicks in at about 2000rpm with a strong surge up to the red line. The engine doesn’t sound pleasant when revved though, so that generally means trying to change gear when you get to 4000rpm. Keeping the engine in that power band does require a bit of planning and careful thought and if you fail to do this, boost is lost and performance is suddenly rather sluggish.

This isn’t a car for bombing down tight, twisty lanes then. It just becomes too much of a chore trying to keep the boost in play. I’m finding this car is at its strongest on faster, more open stretches of road, where you can keep the average above 45mph. Then you can stay in top and the turbo is always on boost – so acceleration is always strong and the engine feels eager and responsive when you need it to be.

Overall though, I think I do prefer it. I’m a big fan of the normally aspirated diesels, but there are always times when you wish you had just a little bit more go. Usually when overtaking or climbing steep hills. There’s a steep hill near here that the BX will climb briskly in top gear. No other car I’ve owned gets close to that. My V8 Land Rover would struggle in fourth!

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