Beef 'n' chips

Tuning is no longer the preserve of baseball-capped boy racers - now that the diesel engine can be tuned for a faster, better and altogether meaner performance, there'll be few petrolheads turning in your direction, predicts Ivor Carroll

There was a time - not all that long ago - when the notion of ‘tuning’ a diesel-powered car for better performance was not only non-existent, but would have raised a guffaw or two. Even though it’s still the case that normally aspirated diesels can’t have much (i.e. anything) done to them to up their power, turbodiesels hold plenty of opportunity for power upgrading.

Strangely enough, commercial power upgrades didn’t really exist before the advent of electronic fuelling control on diesels, but now that electronics are so widespread, a plethora of diesel ‘chippers’ has sprung up. But why? That’s not so easily explained, for after all it was always possible to increase turbo boost, increase pump fuelling accordingly and, if one was really stuck for further ideas, increase intercooler size too. You see, you can keep on packing air into a turbodiesel’s cylinders providing the air doesn’t get too hot, providing you can match the air with sufficient fuel, providing the engine will physically stand the pressures generated.

But electronic control has in many cases made it easy to increase boost and fuelling without even getting one’s hands dirty (in some cases the turbocharger wastegate is controlled by an electric valve so you don’t have to fiddle with the wastegate itself). And in many cases the alteration of the fuelling ‘map’ held in the fuel system’s Electronic Control Module can improve driveability and increase torque.

WE AIN’T SEEN NOTHING YET

Today there are tens of companies in the UK marketing diesel power upgrades of this ilk, but we ain’t seen nothing yet. To kick off what may turn into a reasonably regular foray into the world of diesel performance upgrades, we’ve tried out two modification for the 90bhp TDI engine used in Vws, Audis, Seats and even the Ford Galaxy MPV.

The first, known as Torqmaster, is from Webcon of Middlesex (that’s a contraction of Weber Concessionaires, the carburettor and fuel injection people) and the second - know as the TDI Powerchip - comes from Darley Specialist Services in Derby.

Webcon quotes a power increase of 20bhp for its mod, and torque that is upped by 47Nm. Torqmaster comprises a mystical black box connected in line with the injection pump harness and an air pipe emerging from the box, teeing into the wastegate pressure pipe on the intake manifold.

The second power modification module is a black plastic double-ended plug about one inch square. It simply plugs in-line with the loom that goes to the fuel injection pump. Unplug loom, plug module on end of loom, and plug the lot back into the pump - voila! It takes about 10 seconds. This device also has ‘secret’ contents, although reading between the lines there’s probably little more fancy inside than some resistance’s which shift fuelling and boost parameters. I wouldn’t swear to it, though!

A power figure of 113bhp is quoted for the TDI Powerchip, but torque is unknown. Suffice it to say there’s a fair bit more of it. It’s cheaper (at £295 all inclusive, against the £447 of the Webcon) and less complicated than the Webcon arrangement, but our performance-testing equipment tells us it’s also a little less effective.

We tested a Golf TDI equipped with the Webcon device first, and were immediately impressed by the feeling of solidity it bestows on the standard TDI90 performance. As yet there is no such thing as Golf TDI 110, but when the fourth generation car arrives, we think it will feel like this. The difference wrought to performance is really quite large; disconnect the mod and the Golf feels flat and thin underfoot - not the usual description of a Golf TDI! There’s no doubting that engine response from very low revs is much enhanced (as with the super-responsive TDI 110), which means there’s a solid wall of torque available virtually from idle, and the need to change down gear (not a frequent need on a TDI) is further reduced. Incidentally, a version for the 110 engine is also available.

RUNNING OUT OF BREATH

The much-bolstered torque curve is probably most apparent when you’re pounding the middle land of a motorway at 70mph, where a gentle squeeze of the accelerator has the car pulling forward with great deliberation - no need for the gear stick. And at this kind of road speed the Golf is only doing about 2,500rpm.

With the Webcon power modification you rarely ever take revs beyond this speed anyway, such is the muscle produced below. Interestingly though, if you do venture up to the giddy heights of 4,000rpm or even higher, you will find the TDI engine keener than usual; clearly the ‘mod’ enhances the torque curve all the way, allowing a useful extension of pulling power beyond the 4,000rpm at which the TDI 90 traditionally runs out of breath.

So what we’re looking at overall is a driving characteristic virtually identical to that of the TDI 110 engine, with neither the variable-geometry turbocharger nor the £1,00 premium that exists, for example, in the Audi A4 TDI range! Not that this deal is premium-free. However, that meaningless old adage ‘Cheap at half the price’ actually seems to fit perfectly in this context!

You can read the impressive acceleration times in the accompanying table, but for the time being, what of the TDI Powerchip’s achievements? Actually, the comparative acceleration times virtually tell it all, the Powerchip enhancing acceleration tow-thirds as well as the Webcon device, for - spookily enough - two thirds of the price! Click into place the TDI Powerchip and this is what you get: beefed-up pulling power from right down low and an urgency to pull forward.

GET-UP-AND-GO

One of the most noticeable things about the torque enhancement is that you’re aware at all ties of not having to push the accelerator pedal as far as you used to. Trying the Powerchip on the Golf immediately after the Webcon device definitely take the edge off the car’s get-up-and-go, but subsequently driving the Golf unmodded is a quite sad experience! the Powerchip seems to do much the same job as the Webcon, but not quite as well, and with it the extension of the engine’s useful rev-range is not quite as apparent either.

There is one other wee criticism to be made of the TDI Powerchip, which is that at around 1,200rpm under steady-state throttle the engine chugs and hunts very slightly, possibly suggesting slight over-fuelling. However, this is rarely experienced (you don’t spend long at 1,200rpm) and it really is slight. It’s important to point out that neither modification made any visual difference to smoke output (even under full bore) nor to engine smoothness and sound.

So what we end up with is a power-mod twin-test which was never really a valid comparison test to begin with; horses for courses is the result, and you really do get what you pay for in each case. If you want to put useful extra spring into your TDI’s step (that’s any car powered by the 90bhp TDI engine) but the though of spending more than £300 in doing the job is too galling by far, the TDI Powerchip is a worthy solution. On the other hand, if you want real beef with your chips, a TDI 90 will don muscular livery indeed if equipped with the Webcon Torqmaster (code WDVW03E), for £447.

Test Results