So far in this series we’ve covered building a new intake…
… and fitting a new (second-hand!) rear muffler.
The results of those modifications, while on paper clearly benefitting intake and exhaust flows, actually caused the car to have less performance.
The likely reason?
The additional air wasn’t being compensated for by the engine management system, and so power was lower.
If that idea was correct, you’d expect reflashing the engine management system to add lots more power – and that’s just what happened. But first let’s take a step back.
The Volkswagen 1.9 litre PD diesel used in the Skoda Roomster guinea pig is an engine that has been around for a long time. It’s also well-known and outside of Australia is often reflashed.
Given that there are plenty of off-the-shelf maps to suit this engine, I approached Wayne Besanko of PowerChip, an Australian company with strong overseas links. I asked what he had available for the 1.9 litre diesel but instead of offering one of the imported programs, he was eager to custom remap the engine management, with his guru Bill Ingram doing the work. Furthermore, he was prepared to fly Bill (and it turned out, another PowerChip employee) to Canberra to remap the engine management on a local dyno.
It was an attractive offer, especially when compared to using an off the shelf program. (And in fact it was because this custom tuning was going to occur that I embarked on the intake and exhaust mods, knowing that the tune could be matched to these changes.)
The dyno that was used belongs to ESP Racing in Queanbeyan (just over the border from the ACT in NSW). Glen Kelly drove the car, Bill Ingram tuned it and Gary Mannion (a PowerChip technician in training) watched on. All runs were made from 1000 – 4500 rpm in fourth gear with the dyno set to diesel forced aspiration mode.
Prior to coming to the dyno, Bill had identified the Roomster’s Bosch EDC15 ECU and the program used within it. He’d also isolated about a dozen maps that could be altered as required – these maps included injector fuel flow, injector timing, boost control, smoke control and torque limiting.
A dyno run of the car prior to tuning showed a peak power of 77kW at the wheels – a surprisingly good performance given the slight loss in on-road acceleration recorded after the intake and exhaust mods, and also given that the factory claims 77kW at the flywheel. (On these Dyno Dynamics dynos there is typically a 25-30 per cent loss in peak power between the flywheel and rollers – losses caused by the transmission and the deflection of the tyres over the relatively small diameter rollers.)
After downloading the factory program via the OBD port and confirming its characteristics, the first tuning step was to change two maps - reducing the factory torque limiting and slightly increasing the amount of permitted smoke.
After these changes were uploaded (again through the OBD port), a dyno run revealed an immediate peak power gain of 13 per cent – now there was 87kW at the wheels!
With no specific changes having been made to boost or fuelling, this was an interesting and impressive gain. (Of course, making these changes to the smoke and torque limiting maps would have resulted in more actual fuelling, but the factory fuelling maps were still the ones being used. In fact, the dyno showed a drop in AFR from typically 19.5:1 to 17.5:1)
Further tweaks were then made to the torque limiting and smoke maps. The amount of low-down, full-throttle smoke was decreased until it was not discernible, while just a trace of black diesel smoke was permitted at the top end.
Bill spent a little time trying to dial-out the overshoot in boost that occurs around 2000 rpm; however, completely curing this would have required more time than was available.
The final power curve shows a maximum of 91kW available from 4000 – 4500 rpm, with a strong gain in power from 2000 rpm upwards.
Interestingly, no time was spent tuning at light loads, and no driveability testing was carried out on the dyno.
On the Road
On the road the result is staggeringly good: the car drives utterly and completely like a factory standard car except with more power.
That’s especially significant as prior to the tuning, I’d had a number of concerns.
First, I was concerned that after the reflash, turbo boost would come on with a much greater rush. That was a worry because such behaviour, while it always makes a car feel much faster, also makes throttle control more difficult and can easily (especially in a diesel front-wheel drive) result in wheel-spin. (And if the wheels are spinning, you’re not accelerating as well as you could!)
But post-reflash no such behaviour in boost development occurs on the road. In fact if anything, I’d say that in most gears, boost comes on with less of a rush (ie is more linear) - probably as a result of Bill modifying the low rpm fuel and smoke tables to try to get rid of the dyno boost spike.
Secondly, I was concerned that with more power available, the very smooth and effective cruise control would become jerky. That is, it would surge, over- and under-shoot. Cruise control is important to me as the car spends probably 70 per cent of its time on country roads in cruise control.
But the cruise control is as smooth as it was prior to the reflash.
Thirdly, in light throttle conditions between 1000 and 1500 rpm (where the engine runs in urban conditions), I was concerned that the factory smoothness and tractability might be lost.
But in these conditions the car is clearly better than it was before: bottom-end torque is improved. For example, the car will happily trundle along in fifth gear at idle speed, foot right off the throttle! The practical outcome of this is that when driving on tiny throttle openings (for example, keeping station with traffic at 50 km/h on a flat road), the car can be left in fifth gear and driven seamlessly and smoothly at 1000 rpm… so gaining excellent fuel economy. There are no stutters, hunting or lumpiness.
So in day-to-day driving conditions the car is much better than standard with no driveability downsides at all.
But what about performance? You don’t add about 20 per cent more power through a lot of the rev range without the car being substantially faster on the road – and so it proved!
The Roomster is no performance car – and was never meant to be. But after the reflash, the engine is stronger throughout the rev range and revs far more freely to the redline of 4500 rpm. Prior to the reflash, there was no point in going past 4000 rpm – the power just died above those revs. But now the redline can be used as the gear-change point.
I would rate the on-road results of the reflash as 10/10.
But what about on-road acceleration?
As covered in previous parts in this series, this is a measurement made throughout the rev range in second gear, showing at every point how much full-throttle acceleration is occurring. The resulting graph is the same shape as the torque curve of the engine, but unlike a tractive effort measurement made on the dyno, it takes into account actual intake flows caused by the new intake duct being pressurised by the forward motion of the car, the efficiency of the intercooler, the rate of boost increase and so on.
This graph compares the standard car (blue line) with the car equipped with intake, exhaust and reflash (red line). Remember, this is the actual on-road acceleration.
As can be seen by the red line, there is an improvement in acceleration at every point in the rev range from idle to the redline.
Because I didn’t then go back and fit the standard muffler and intake, I can’t be sure how much of the gain comes from each modification component. But it seems likely that the massive top-end improvement can be sheeted-home at least in part to the better flows coming from the intake and exhaust – it just needed the fuel to make it happen.
As always, fuel economy is hard to quantify, however it appears that with the reflash it has improved. Fuel economy was measured over a frequently driven 60 kilometre stretch of country road. The table shows the results, which include a change of tyre diameter (and so an alteration in the displayed average fuel consumption).
So, comparing apples with apples, the fuel economy of the modified car is about 5 per cent better than standard.
I am ecstatic with the results… and I am someone not easily pleased!
As noted below, PowerChip made their tune available free of charge. But even at the commercial rates (AUD$1290 inc GST) I think the combination of the three mods would be well worth it.
That’s because, with the intake and exhaust modified so cheaply (AUD$100 total for both), the overall cost of the modifications is low for the outcome achieved. (But I wouldn’t have been so happy had the exhaust cost $1000 and the intake $300!)
Compared to standard, the car now has:
But what is now limiting the real-world performance is the standard intercooler. With intake air temperatures in normal on-road use 40 degrees C above ambient, and when going hard no less than 60 degrees C above ambient, the car is crying out for an intercooler that can keep intake air temps low on sustained loads…
In Part 5 of this series: fitting a new intercooler... and the series conclusion