The “turbo man” of Buchloe

Interview with Professor Fritz Indra

The B7 turbo engine from ALPINA – a milestone in German engine history. In the 1970s, Fritz Indra developed a petrol engine with combined turbocharging that made the BMW ALPINA B7 Turbo the fastest series-production saloon of its time. We sat down with the developer of this engineering masterpiece.

Burkard Bovensiepen with Prof. Fritz Indra

Professor Indra, let’s start with your career at ALPINA: In 1971, you decided to leave the bright lights of Vienna for the tranquillity of Buchloe. You were working as a university assistant at the Vienna University of Technology, and joined ALPINA as the Head of Development. How did that come about?

First of all, I knew very early on that I wanted to be an engineer. While I was still in primary school, at the age of 10, I laid out my career plans in minute detail in an essay. Incidentally, I misspelled the word “doctorate” so badly that you couldn’t even see it for red pen. But that’s exactly what happened: after graduating as an engineer, I had the good fortune to be accepted as a university assistant in Vienna, where I was able to do my doctorate. There was nothing happening in Austria back then. There was no BMW plant in Steyr yet or anywhere else for wholehearted petrol engineers like me.

To keep my head above water as a university assistant, I had four or five part-time jobs. One of these was writing articles for the Austrian car magazine Autorevue. In 1971, they asked me to write an article about a certain Burkard Bovensiepen. So I travelled to Germany for an appointment, and Gert Hack was also there. At that time, he was on the executive board of ALPINA and of course he’ll be well known to many as a journalist for AUTO MOTOR UND SPORT. And he was the one who asked me: “What do you actually do?”. Well, I have a doctorate, I know a lot about exhaust gases and exhaust regulations – that’s what I did my doctorate on – for motorsports too – and I developed the Kaimann for Kurt Bergmann while I was studying. And just like that it became clear: this made me a perfect fit for ALPINA. The deal was done so quickly that I started at ALPINA as Head of Development three months later. In Buchloe, a small village in the Allgäu. When I took my wife there for the first time, coming from Vienna, she sat down on the main thoroughfare of Buchloe and burst into tears.


A milestone in your development work at ALPINA was the B7 turbo engine. So how did it come about that the first petrol engine with combined turbocharging was developed in Buchloe of all places? Fundamental research isn’t necessarily something you expect from a small-series manufacturer.

It really came down to Burkard Bovensiepen’s vision for ALPINA: he never wanted to be perceived as a tuning outfitter; he wanted to make ALPINA a recognised automobile manufacturer, which he ultimately succeeded in.* And of course you also have to back this claim up, you have to be innovative. Just making cars faster was never the be-all and end-all for ALPINA. And simply adding more displacement to an ALPINA engine to increase the power just wasn’t the right answer at the time. Because certain noise and emissions levels applied in the 1970s too – it wouldn’t have worked anyway. And there was no easy way of squeezing more power from the BMW six-cylinder naturally aspirated engines of the time, which only had two valves per cylinder.

It became clear to me then that turbo technology was the perfect answer: significantly increasing power while keeping displacement the same, in order to also meet all statutory requirements. However, turbochargers were still a novelty at the time. A few manufacturers had already made attempts at the technology, but those engines ended up being incredibly unresponsive, really fuel-hungry and on top of this kept breaking down. I thought to myself we could do better.

Then all the pieces started to fall into place. The successes we had enjoyed at the time in motorsports were of course a huge advantage. We had a very big network around us, with committed partners and suppliers who wanted to share ALPINA’s success. Everything went hand in hand, and we were able to combine very different technologies: From the air intake resonance system designed by Dr. Gyula Cser to a fully electronic map ignition system – a completely new innovation at that time. The end result was a neat turbo engine suitable for everyday use that was first used in the BMW ALPINA B7 Turbo. 


Exactly what changes had to be made to the existing turbo petrol engines to make them – as you say – “suitable for everyday use”?

If you looked at the weak points of the turbo engines from that time, you would have seen how a number of modifications were needed. So the ALPINA B7 engine used a variety of new technologies. For example the injection system: tests revealed how important precise fuel metering is in the turbo engine – not just for the consumption, but also for the responsiveness. The injection system therefore had to be able to register both the air density and the air volume, in order to be able to meter the fuel perfectly. Here I insisted on the enhanced mechanical DL injection system from the company Pierburg. But the arrangement of the injection system was important too: locating it downstream of the compressor changed the pressure differential. The turbine speed decreased, which shortened the time required for turbine startup and improved the responsiveness. Thermal stability was ensured by an intercooler. I employed an air-to-air system here. But the intake air temperature had to be right too and thus the arrangement of the intercooler, because this had a huge influence on power and fuel consumption. Our partner Kühnle, Kopp & Kausch (KKK) also developed a new turbine housing to our specifications. We needed to adapt the geometry because we could see that a smaller throat diameter would be beneficial in the low and medium rpm range in particular.

Another problem was that the turbo engines back then were very sensitive to knocking. The ignition timing was crucial here. However, you couldn’t control it precisely enough with the existing ignition systems. So we turned to the system from Dr. Hartig – a fully digital, computer-controlled map ignition system, an absolutely innovation in automotive engineering. It made the tolerance band much narrower, and the ignition timings much more precise. This meant we had the knocking behaviour under control, but unfortunately the idling was still unstable. The fuel/air mixture just didn’t provide enough turbulence. So I started working with a pinch point in the combustion chamber. This resulted in more thorough mixing of the air and fuel, and the combustion in all six cylinders was more uniform as a result.

And then there was also the air intake resonance system by Dr. Cser, which I mentioned already. ALPINA was the first to use this system on a petrol engine. In a six-cylinder engine, it divides the intake system into two groups of three cylinders each. The inlet ducts then each terminate in a separate resonator vessel, which is joined to the pressure side of the turbocharger via a resonance pipe. Simply put, this generates oscillations in the resonance volume, which changes the air density. This worked surprisingly well over a very wide rpm range. And fixed the problem of turbo lag. The performance curve was impressive – head and shoulders above the other turbo engines of the time.


The fruits of your labour ended up being the “fastest saloon in the world”. A title that made everyone in the industry sit up. What was your perception of the response to the ALPINA B7 engine?

That’s right, there was a huge response from the media to the B7 Turbo. And an unbelievable number of comparison tests. The B7 Turbo came out on top in all of them, even against heavy hitters like the Porsche Turbo, the Jaguar XJ12 and so on. Although the B7 saloon turned out rather restrained - the perfect understatement car. But we had proof for once and for all of it being the fastest saloon of the time. Let me tell you, measuring the top speed was a real adventure back then. I was behind the wheel of the B7 Turbo, with an official from the TÜV ** sitting beside me with a stopwatch. Back then, the measurement was still done “in the wild”. We often used the east ring road in Munich for this, which wasn’t even finished at that point. Whenever we hit the 250 km/h mark, a lorry would pull out in front of us. So it took a few tries until we reached our top speed.

And of course the ALPINA B7 turbo engine led to my reputation in the industry as the turbo expert of Buchloe. I published several articles about this engine. That’s how I came to the attention of a certain Ferdinand Piëch, who at that time was a division manager at Audi. He rang me and said: “I need a turbo man”. And that’s how I became the Head of Engine Development at Audi in 1979.


Interested in learning more about the ALPINA B7 turbo engine? You can read Fritz Indra’s article on this topic in the Automobiltechnische Zeitschrift (ATZ, issue 4/1978, available only in German): “Development of a turbocharged petrol engine for passenger cars with a litre capacity of 73.5 kW”


*ALPINA was accredited as an independent car maker by the German Federal Motor Transport Authority in 1983 (editor’s note).
** German Technical Inspection Association (providing inspection and product certification services, editor’s note).

About Professor Fritz Indra

Professor Fritz Indra, born in 1940, studied mechanical engineering at the Vienna University of Technology, where he completed a doctorate in 1969 in the technical sciences. After working as a university assistant for a time, he joined ALPINA in 1971 as Head of Development. In 1979, Ferdinand Piëch persuaded him to join Audi, where he worked as the Head of Engine Design until 1985. He then moved to Opel. From 1997 to 2005, he was the Executive Director of Advanced Drivetrain Technology at General Motors. In 1991, he was awarded an honorary professorship in internal combustion engines by the Vienna University of Technology. His broad knowledge and global network mean that he is still in demand today as a speaker and consultant in the automotive industry.

Exhaust gas turbocharging diagram for the ALPINA B7 engine
Influence of various boost pressure levels on the performance curve and a naturally aspirated engine with the same displacement for comparison.
Influence of the resonance pipe and combined turbocharging on the performance curve