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Special Feature : Tech focus: Turbo engines explained

Tech focus: Turbo engines explained Tech focus: Turbo engines explained

Mon 23rd May 2011 There are two types of engine in the 2011 Dunlop MSA British Touring Car Championship turbocharged and normally aspirated. Here we explain what that means and why it has been such an important part of the season so far.

By Matt Lamprell

There has been much talk of turbos in the early stages of the 2011 season and the differing views can make it difficult to understand the facts. We enlisted the help of Mountune Racing's technical director, David Mountain, to help us get to grips with it all.

Mountain founded Mountune back in 1979 and the company boasts an impressive list of motorsport clients. In 2011, the Essex-based company is responsible for the turbocharged NGTC-spec engines being used by Team Aon and Airwaves Racing.

So far this year, there have been eight 'full S2000' specification cars on the grid (five Chevrolets and three BMWs), while all others are running NGTC engines either coupled to an S2000 chassis, or as part of a full NGTC package.

David Mountain, Technical Director, Mountune Racing

NGTC and S2000 engines both have a capacity of two-litres the difference comes in the way that they inhale air. The S2000 units are 'normally aspirated', while NGTC engines have the benefit of a turbo charger but what exactly does this mean?

Mountune's David Mountain explains: "With a normally aspirated engine, you've only physically got the pressure on the day. That's roughly one atmosphere. It changes a little bit with high pressure days and low pressure days, but really you're pretty much reliant on the pressure of the day.

"With a turbocharged engine, the turbocharger actually pressurises the inlet system. That makes a massive difference to performance, and more importantly, to the torque of the engine. At low engine speeds, you can get quite incredible torque figures. Therefore, any slight change in boost pressure even quite a small change, say 50 millibars makes a noticeable difference to horsepower and torque."

2011 is the first of several 'transition' years for the BTCC. It's a phrase that has been used before in relation to the BTCC notably for Super Touring to BTC (2000/2001) and more recently with the introduction of S2000 and the switch to NGTC looks set to be just as turbulent as either of those.

When the NGTC regulations were revealed back in June 2009, they stated: "Performance parity will be maintained with current S2000 cars until 2013, after which time the performance level of the NGTC car will be increased."

It is this concept of parity that has caused such controversy this year. Jason Plato won the first two races of the year at Brands Hatch in his S2000 Chevrolet Cruze, but the timesheets have been dominated by turbo-powered cars. After three meetings and 18 competitive sessions, (nine races, three qualifying sessions and six free practice sessions), the statistics speak volumes.

Turbo-powered (NGTC-engined) cars have set the fastest lap in 17 sessions, with Plato quickest in just one his third race victory at Thruxton. However, the BTCC's sporting regulations were written to cover this eventuality - Article 1.11.2.a of the 2011 BTCC sporting regulations states:

The throttle body size and/or restrictor and/or the maximum permitted rpm and/or maximum permitted turbo boost of individual cars may be subject to review at any time during the currency of the 2011 Championship by the Administrator who may implement a variation by way of a Bulletin issued by the Co-ordinator giving a minimum of 24 hours notice.

It is perhaps no surprise then, that ahead of the Thruxton meeting at the start of May, the turbo-powered runners were pegged back. All turbo-powered cars had their boost pressure reduced by 0.1 bar back to David Mountain to explain precisely what that means.

"If you say at Brands Hatch and Donington, we were allowed to run 1800 millibars of pressure that's 0.8 bar over atmospheric pressure - at Thruxton, we had to run 1700 millibars, so 0.7 bar over atmospheric pressure.

"That's quite a big change. You're talking in the region of 10 to 12 horsepower and probably 15 Nm of torque."

"Torque is what propels the car out of corners; what accelerates the car. The horsepower is its ability to maintain acceleration at higher speed. In fact you will see quite a difference from both aspects. One on how fast the car will accelerate from a low speed to a medium speed. Then you will see a difference with the car's top speed, which you will see on the speed traps."

The regulations allow for multiple changes to the permitted boost level during the course of the season. The impact of the first change at Thruxton will be a useful marker for the BTCC's technical team, but it's a complicated scenario, because another reduction of 0.1 bar could have a different result.

"It's not linear", said Mountain. "It's not that simple. There's no real rule of thumb. Also, some engines will be affected more than other engines. It's very difficult to judge.

"There could be some differences. Although reasonably small, there could be some differences. It depends on how efficient the base engine is. I think it's far to say the Honda base engine is particularly good. The Ford is also a good engine, but you could have a situation where you have an engine that's not particularly efficient, so any reduction in boost at any level is going to hurt it more than an engine that is more efficient."

It is clear that much will be said about engines throughout the 2011 BTCC season, and it is often complicated, especially when you have to separate the fact from the fiction. Hopefully, this article has explained the basics.

Got more questions? Get in touch with us, either by commenting below or on Twitter: @btccpages.


Here's a few useful definitions that might help with understanding the engine situation.

Bar (bar) = Unit of pressure roughly equal to the atmospheric pressure on Earth at sea level.

Millibar (mbar) = Unit of pressure. There are 1000 millibars in one bar.

Atmosphere (atm) = Unit of pressure. Equal to 1.01325 bar.

Newton Metre (Nm) = Unit of torque, also called a 'moment'.

Horsepower (HP) = Measurement of power. Varying definitions between 735 and 750 watts. Metric horsepower is close to 735 watts, also roughly equal to one PS (Pferdestarke).

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