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One Man's Car

Optimising a car for a dedicated purpose

By Julian Edgar

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It won’t surprise any of you when I say that modifying your car is about making it what you really want.

I write that in the context of having owned my car, a 2008 Skoda Roomster 1.9 TDI, for a year. And, frankly, I am amazed at how many modifications I have performed in that time.

I didn’t buy the car to modify; I bought it because (as recounted at The Roomster Nuts), I loved the combination of space, practicality, safety and fuel efficiency. (And how did I know the car had all those things? My wife already owned one.) So for me, in standard form it was already a car that ticked plenty of my boxes.

But here I am a year later, having made a heap of mods! Let’s take a look at them – and their success or otherwise….

Use

But before I talk about what changes I have made, perhaps a word on what use the car is put to.

I live about 80 kilometres outside Australia’s capital of Canberra and drive to that city about two or three times a week. Typically, I leave home at 7 am and reach Canberra at about 8 am. In the afternoon, my departure time can be anything  from 4 to 5.30pm. (The difference is important: at the later times I meet plenty of traffic in the city. Earlier, it’s a free run.) But overall, almost all of my kilometres are at the open road speed limit of 100 or 110 km/h.

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Over a year, many of those kilometres are travelled in the dark, and many are when I feel tired after a hard day’s work. (The latter is an important consideration in a car: it’s not a situation when you want a twitchy, hyper-reactive machine.)

If you don’t know the area, you may be surprised to know that you need get only 20 or 30 kilometres out of Canberra and you are then on Australian country roads. No freeways, no islands down the middle of roads; just bumpy narrow blacktops often spotted with errant birds or kangaroos or sheep.

So the roads I travel vary from quite poor secondary roads to four lane freeways, with perhaps 20 per cent of my kilometres (but a larger proportion of my time) done in city conditions.

Power

Among my first Roomster modifications were ones aimed at gaining more power.

The Roomster has a mass of 1260kg and in diesel form, an engine that develops 77kW at 4200 rpm and 240 Nm at 1800 rpm. In the driving, the engine always feels more powerful than these figures suggest - the result of good bottom-end torque that gives immediate engine response.

But where outright power is need – like when passing on the open road – the standard engine is not scintillating.

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I made and fitted a larger airbox intake…

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…and replaced the standard muffler with a small straight-through resonator pinched from a Jaguar. Curiously, these mods resulted in no on-road performance gain – the standard engine management was holding things back.

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However, a custom Powerchip reflash on the dyno fixed that, big time!

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I then added an ex-Falcon XR6 intercooler.

The overall results were unambiguously excellent: a strong increase in power throughout the rev range, and better fuel economy. And all with absolutely factory driveability.

In the real world, as opposed to dyno runs or acceleration testing, I found that with the power modifications I could keep up with the traffic while short-shifting around town (eg changing up at 2000 rpm) and on the open road, pass other cars in 4th or 5th gears, rather than slotting back to 3rd gear as is required with the standard car.

Happy? I rate the performance mods as 10 out of 10.

However, it all turned to shi%$ when I had the cam belt replaced at 105,000km. All that I had gained in driveability and fuel economy disappeared, to be replaced with a free revving, relatively torqueless and thirsty diesel.

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I did some research to find that, firstly, these Pumpe Duse diesels are incredibly sensitive to cam timing, and that secondly, the factory provides the facility for infinitely variable cam timing adjustment. After I tweaked the cam timing (just by small and careful movements followed by road testing), the performance outcome was even better than before.

I reckon that with my fine tuning of cam timing, the engine is a fraction down in outright performance over what was achieved straight after the major modifications. But it has brilliant torque from about 1100 rpm, revs easily to the redline of 4500 rpm, and delivers exceptional fuel economy.

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For an old, SOHC non-crossflow diesel, the performance/economy of the Roomster is now really outstanding – in fact a better fuel economy / performance outcome than I used to achieve with my NHW10 petrol/electric Prius… both when that car was naturally aspirated or turbocharged! (And compared with that [older] Prius, the Roomster has a lot more room and better handling.)

Let’s put it all in ‘real world’ terms: in the Roomster I can drive my country/city commute at the speed limit and get 5.3 litres/100 km. Or I can drive damn hard (I am not going to tell you the speeds, but I am going along nicely) and still get about 6 litres/100 km.

But I wouldn’t ever call the car’s powerplant ‘refined’. Instead, it’s an olde world diesel - and it feels pretty much like that.

Engine performance modifications summary

The good: brilliantly useable performance, excellent fuel economy, better than factory driveability

The bad: it’s never going to be a refined engine

Brakes and Wheels

The Roomster is a weird car. Sure it looks weird, but it was also built by Skoda on a budget – and so it uses proprietary Volkswagen/Audi engineering for almost all of its mechanical bits. In a modern context, that’s the weird part.

Rather like Nissan/Datsun in the Seventies and Eighties, where there was huge interchangeability of mechanical bits under the skin, with the Roomster, upgrades are often a case of asking: what other VW/ Audi / SEAT / Skoda bits will fit?

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So it was the case with brakes. After struggling along with misinformation and buying bits that didn’t fit like everyone said they would, the end result was actually very easy. Just buy factory Audi S3 front callipers and their dedicated calliper mounts, then match these with Audi S3 RDA grooved discs and EBC ‘Red’ pads. All the bits then bolted straight on…

However, even with the aftermarket parts supplied to me at trade price through a friend, the end result wasn’t cheap.

But boy it works!

I don’t want to sound overly smug, but like the engine mods, the braking performance is simply a 10/10 upgrade. No problems with brake balance, no problems with brake pedal travel. Better feel, better retardation… better everything.

Everything, that is, except ride quality.

The bigger brakes and callipers added 1.2kg to each wheels’s unsprung weight – and that’s an issue. As in fact I found at out with the new wheels and tyres…

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Before I could increase the size of the front brakes, I needed bigger wheels. Watching eBay, I found some factory wheels and tyres from a Volkswagen Vento. The wheels were 16 inches in diameter, styled in a bold simple way I liked, and came with 205/55 tyres that still had some tread life left.

They bolted straight on (and that’s what I’d been most concerned with: stud pattern) and the speedo, which previously had been rather optimistic, now became accurate. In other words, rolling diameter had increased.

But along with rolling diameter, unsprung weight had also gone up. Bigger and heavier wheels, bigger and heavier tyres. And I could clearly feel the difference.

If you aren’t used the sensing unsprung weight changes, it’s very hard to describe the sensation that results from increases in unsprung weight. Basically, wheels feel like they fall into holes. Another way to say it is that it feels like the car is being shaken by the wheels, rather that the wheels doing the shaking and the car not moving vertically.

And with the new wheels and tyres, there was more mass bobbing up and down – that was for sure.

And the rolling diameter wasn’t up just a bit – it was up a lot. As we discovered when we fitted new Pirelli P7 tyres and then tried to fit snow chains… there was simply nowhere enough clearance.

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So with the new wheels and tyres, unsprung weight was increased – and, I subsequently discovered, so was wheel offset. The latter resulted in a lot more feedback through the steering. On the four lane freeway on which I drive, that added feedback is great. But on the rough, narrow two-lane bitumen, that feedback can become borderline excessive.

The bigger wheels and tyres were needed to provide brake clearance. And the wider rubber on the road gives more grip. But the result in not unambiguously good: there’s more feedback thorough the steering (and sometimes that’s not wanted) and the ride quality is clearly poorer.

Brakes and wheels/tyres

The good: superb braking performance, excellent braking feel, more road grip

The bad: poorer ride quality, sometimes steering feedback is excessive

Lights

One area where the standard Roomster is poor is in its headlights. They simply don’t have the penetration or brightness that is needed in this country.

My first upgrade was to Narva ‘Plus 50’ headlight bulbs. As I have found in the past with better bulbs, the difference is pretty minor. It’s worth doing – but it was never going to be the whole solution.

I then added Narva 175 driving lights, using a ‘combination’ kit comprising one spot and one spread beam. For their price and size, these are fantastic lights – the improved high beam performance was massive.

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However, I later decided to go even bigger, fitting Narva 225 lights fitted with Osram HID bulbs and ballasts. The lights needed to be braced in position with extra aluminium straps (otherwise they constantly vibrated – impossibly distracting) but after the straps were installed, the result is just stunning.

The illumination is so bright and far-reaching that for the first time ever when driving at night, I don’t drive looking constantly at the far end of the beam. It’s simply too far away – on straights you’d be looking literally a kilometre ahead!

The lights are so bright that you can even use them at dawn and dusk – the roadside reflectors leap out when you switch them on.

But there are some downsides. Going back to low-beam represents a massive change in illumination which can be a bit disconcerting, and the lights create some extra wind noise at around 80 km/h.

Lights

The good: fantastic high beam performance

The bad: increased aero noise, low beam performance needs further improvement

Bits and Pieces

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The standard Roomster horn is feeble and ineffective. I replaced it with dual horns from a Nissan Patrol.  In my driving I use the horn maybe four or five times a week – mostly to clear the road of birds.

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The standard gearchange is rather long and rubbery. However, a commercial short-shift kit is available for this Volkswagen gearbox and it was quickly and easily installed. It’s also adjustable, so you can get the trade-off between shift effort and shift throw just as you like it.

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As with pretty all cars of the last few decades, the number of instruments on the Roomster’s dash is quite small. I added a ScanGauge that installed in just moments - it plugs straight into the OBD port. I display intake air temp, accelerator pedal opening, coolant temp and intake manifold pressure. 

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I learnt long ago that in a country car, having the facility to listen to trucks and emergency services is very valuable.  To achieve this, I installed a Uniden UBC355XLT scanning radio that has all Australian emergency services and trucking channels pre-mapped. With a 1-metre whip aerial mounted on the front guard, it works fine.

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As with many Volkswagen / SEAT / Skoda products, the radio in the Roomster is a standard double DIN design. This allowed me to replace the single CD radio swap with a 6-stack CD version from a Golf. It screwed and plugged straight into place.

However, the new unit’s illumination is VW red (rather than Skoda green) and it doesn’t interface completely with the car’s CAN electronics – I don’t get the repeat station display on the dash and the system doesn’t turn on and off with the key. I think these aspects can be fixed by car reprogramming (or maybe it’s the addition of a new CAN gateway?) but so far, I haven’t bothered.

Horn, gearchange, instruments, scanning radio, sound system

The good: everything!

The bad: radio lighting colour is wrong and it needs some further tweaking to make it work with existing car functionality

Ride and Handling

Suspension is a ‘work in progress’. I don’t think that in standard form the car is a bad handler, or has bad ride; but after many thousands of kilometres I don’t think either aspect is outstanding.

With my car, with the larger and heavier front brakes, and the larger and heavier wheels, and the lower tyre profile, the ride quality is clearly worse than standard. But my car also has more grip.

But overall, I don’t think that the handling really comes together. The steering is rather slow around centre and it’s a car where (rather like lots of Audis I have driven) you have to be well ahead of the car in your control inputs… taking that approach makes up for the slowness in response. As I said earlier, I am not after a twitchily responsive car, so a fine line needs to be trod.

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My first outright handling modification has been the installation of a Whiteline rear anti-roll bar. Designed for the Mk IV Golf, it bolts straight on. (That’s because the Roomster uses Golf rear suspension.) The added anti-roll bar has sharpened steering response (especially on corner turn-in) and given reduced understeer. On dirt the car will now oversteer on mid-corner throttle lifts or if you turn-in really fast.

The standard stability control system is well calibrated – sufficient to let you slide the car around a little and activate only if you go too far. (Note that the stability control in my wife’s Roomster seems to be far more interventionist.)

But the new anti-roll bar has added more unsprung weight (this time at the back) and has made single rear wheel bumps harsher. Conversely, in some bumps there has been an apparent decrease in roll accelerations (not what I expected).

But it seems to me that the dampers are now wrong. I think the ride/handling outcome would be much better if the high-speed bump damping was softened considerably – and perhaps the springs could be just a tad softer?

Ride and Handling

The good: decent grip, stability control works well, understeer/oversteer balance about right

The bad: ride quality poor – lots more to be done in this area

Ideas

There are lots of things I’d still like to do to the car. In short these are:

Aerodynamics – the drag coefficient of the Roomster is surprisingly good but if I could lower it still further, in my country road driving I think I’d see an improvement in fuel consumption.

Sound system –in addition to making the CD/radio work better with the car’s standard electronics, I’d also like to add a small self-powered subwoofer.

Intercooler bypass – I’ve noticed that fuel economy is best when the measured intake air temp is about 25 degrees C.  Given that the car spends nearly all its time on boost, an automatically controlled intercooler bypass would allow this intake air temp to be achieved in many driving conditions.

Suspension – as described above, I think that softer dampers and/or springs (maybe progressive rate springs?) need to be fitted.

Steering – I think that perhaps the steering could be improved - maybe less power assistance or more castor… things to make the steering more positive at speed.

Conclusion

The modified Roomster is certainly not a car that would suit everyone. But it suits me – and of course that’s just the point…

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