The Rise Of The Small Engine
by David Finlay (29 June 2007)
It's too soon for most people to have noticed it, but the motor industry may be in the preliminary stages of an engine revolution. As fuel economy and exhaust emissions become ever more important, and increasingly a matter of legislation and taxation, manufacturers are paying ever greater attention to the maxim that small is beautiful.
The problem is simple enough to explain. Within a range of cars, manufacturers will generally offer engines of different sizes in the interests of customer choice (or rather to maximise the chances that someone will buy a car from within that range, which is what "choice" really means here).
Some people will be happy with the relatively low performance of a smaller, less powerful engine. Others will prefer a larger engine because of the greater performance, or perhaps because they want a car that is more relaxing to drive. The problem is that, all other things being equal, the larger engine will use more fuel. As our fuel economy testing feature explains, greater fuel consumption means higher CO2 emissions, which in turn means higher rates of tax in all major European markets.
First Volkswagen and more recently Fiat have devised similar solutions, using forced-induction 1.4-litre petrol engines. A 168bhp version of Volkswagen's super/turbocharged TSI unit replaced the previous non-turbo two-litre engine in the GT, and both this engine and a 138bhp derivative have since been used in other Golf and Touran models.
Fiat came to market second with a similar idea, but has been more radical with the application. Every petrol-fuelled version of the new Bravo uses a 1.4-litre engine - a normal 90bhp unit, a turbocharged T-Jet developing a maximum of 120bhp in place of a naturally-aspirated 1.6 and a 150bhp T-Jet instead of a conventional two-litre.
The Volkswagen engines are more powerful because they use larger turbochargers. The turbo lag that would normally result from this is eradicated by the supercharger, which shoves in air at low engine speeds. Fiat, either unwilling or unable to spend quite so much money on development, has made do with just the turbocharger; lag problems are solved by using a smaller, faster-reacting compressor which, however, can't produce quite so much boost at high revs.
But this is just a detail. Each of these engines produces very substantial amounts of power for their size, regardless of the manufacturer. It's difficult to believe that they are really just 1.4s when you drive cars that are fitted with them. However, none of them feels like a car for which high performance is the most important consideration.
That's because it wasn't. What both Volkswagen and Fiat are doing with forced induction is pushing in at least as much air as a normal 1.6 or a 2.0 would be able to breathe in without external help. The irony is that it's what the engines do when air isn't being thrust into them that really matters.
This is because of something else that was revealed in our fuel economy testing feature - in measuring the fuel consumption and CO2 emissions of a car during the official EU test procedure, performance hardly comes into it. The hardest piece of acceleration required is that the car must go from rest to 62mph in fifty seconds.
The Fiat Bravo T-Jet - indeed, any turbocharged car - can do this without the turbo providing any boost at all. A car with the performance of a very healthy two-litre therefore achieves the economy and emissions results of a normal 1.4 - the figures for the 90bhp Bravo and for the 150bhp T-Jet are almost identical.
The Volkswagen story is slightly more complicated because of the supercharger. Superchargers normally operate all the time, so they are providing boost (and reducing fuel economy) even at low engine speeds. But the TSI's supercharger disengages when the engine isn't required to produce much power, which it certainly isn't in the EU test. Since the mechanical link is completely broken, the supercharger neither boosts the engine nor drags it down by creating extra friction.
The result is an engine which, in 168bhp form, is more powerful than the two-litre unit it replaces, but officially has better fuel economy and lower CO2 emissions.
An unspoken message in all this is that it may prove very difficult to match the official economy figures. After all, if the engine feels like it's larger than a 1.4, that's because it's being helped along by the super/turbocharger which had practically no input during the EU test. So what's the point?
Well, you pay for the fuel you actually use, but you pay tax on the CO2 which is assumed to be produced according to the EU test. So, although the fuel bills are likely to be comparable to those of a 1.6 or a 2.0, the Vehicle Excise Duty will be lower.
That's of no great interest to the manufacturers, except in the sense that it makes their cars more appealing to potential buyers. A more important issue is the one about the average CO2 emissions of all cars built in Europe. This has been a subject of debate for a long time. The average in 2005 was 162g/km, and although the European Automobile Manufacturers Association (ACEA) once committed itself to lowering it to 140g/km by next year, that clearly isn't going to happen.
Back in February it was announced that the EU is planning legislation which will require an average of 130g/km by 2012. That was a compromise. Environmental pressure groups, and some EU commissioners, wanted it to be lower. The ACEA described it as "arbitrary and too severe". But if it becomes law, that's tough luck on the ACEA - whose members, it might be noted, include Fiat and Volkswagen. Indeed, the ACEA President is Sergio Marchionne, who also happens to be CEO of the Fiat Group.
Obviously, the Volkswagen TSI and Fiat T-Jet technology must have started development a long time before February 2007. Equally obviously, these particular cars can't bring down the average by much on their own - the Golf GT's official CO2 output, for example, is 175g/km, well above the current above average never mind the proposed one. And right now there are simply not enough of these cars on the road to make a scrap of difference to the average.
But these are early days. TSI and T-Jet are on the market now, five years before the proposed EU legislation would come into force. If Volkswagen and Fiat extend the technology to other cars (which they might - a one-litre TSI Polo has been mooted as a possibility), and if other manufacturers decide to go down the same route (you can bet your mortgage that they are already committed to it), this might turn out to be a way of bringing down the CO2 average to more acceptable levels. Then everybody would be happy, wouldn't they?
Well, they might. But wouldn't it be ironic if average CO2 levels, as calculated from the EU tests, fell below 130g/km, while in the real world the actual amount of CO2 pumped into the atmosphere each year remained about the same as it is now? That could definitely happen, but it's not a possibility you're likely to hear much about as the European CO2 debate rumbles on.
