The mystery of the missing exhaust

The removal of double diffusers in the 2011 regulations meant that Formula 1 designers had a chance to look again at the air flows at the rear of modern Formula 1 cars, with the aerodynamicists experimenting with all manner of new ideas, in an effort to create as much downforce as possible by creating something akin to the blown diffusers of 2010. Renault and, it seems, McLaren have both come up with the idea of having the hot air from the exhausts piped out of the car from the front of the sidepods, rather than from the back as has usually been the case. The aim is to use the exhaust gases under the car to increase the Venturi effect.

The Venturi effect is created when a fluid is squeezed through a small opening and then expands as it exists. By doing this there is a lower pressure area created at back end of the car which has the effect of sucking the car towards the ground. In the old days F1 engineers used “skirts” on the underside of the wings to seal the underside of the car from the outside and thus created a lot of pressure. These “skirts” were banned but the same effect can still be obtained, albeit to a smaller degree. The second advantage is that rerouting the exhaust gases under the car means that the airflow at the back end is much neater and so there is less disruption of the flows to the rear wing and that means that these will work more efficiently.

The aerodynamic paraphenalia one sees at the front of the modern F1 cars is designed to create a high pressure of air in the area in front of the flat floor of an F1 car, thus increasing the pressure of the air being forced through between the floor and the ground. The diffusers used in the past were designed to maximise this effect. Now they are gone, the best way forward is to force as much air as possible under the car and adding the exhaust gases is going to help, as long as the layout does not create problems elsewhere with the heat of the exhausts. This means that there need to be some pretty efficient insulation to avoid the heat playing havoc with the electronics, the fuel tank, radiators, batteries and the rump of the man driving the car.

To illustrate the problem one can go right back to the 1920s when engines were at the front of the Grand Prix cars of the day and in 1925 the Delage engineers placed the exhaust piping close to the metal cockpit with the effect that the drivers suffered not only burns to their feet from the metal cockpits, but also heat exhaustion and in some cases losing consciousness. There were several races in which reserve drivers had to be used and, if my memory serves me correctly, one race where the team actually ran out of drivers and had to ask someone in the paddock to take over. Fortunately Andre Dubonnet was there. He had never driven the car before and had no racing suit but after a hasty discussion he departed the pits at the wheel of a Grand Prix car, wearing a lounge suit…

The point of interest (and this is way beyond my technical abilities) is that there seems to be some advantage gained by using hot air to seal the underside of the car from the external air, so that the exhaust air running along the undersides of the floor, makes the cooler air in the centre travel faster and thus create more downforce.

Ross Brawn says that his designers have been looking at similar ideas and says that if it works out as a better idea it is easy to implement as it would not require a change of monocoque, unless of course there is some fancy insulation built into the chassis itself…

37 thoughts on “The mystery of the missing exhaust

  1. Now thát’s innovative thinking. Whether it’s of much use to the automobile industry, I doubt. And I reckon the average fan doesn’t really care, either. I love it, though. 🙂

  2. I seem to recall a comment during the Ferrari launch (which Google is stubbornly refusing to find any trace of) that 1 of the many things they were likely to change before the first race was the exhaust layout.

    At the time I assumed it was related to last years fashion to have them under the car, but perhaps they are also working on a similar scheme even before seeing it on other cars.

  3. Really interesting article Joe.

    Won’t this also mean the driver is subject to a much, much higher level of engine noise than he was in the past?

    Exhausts on the edge of the cockpit would be close to deafening I’d have thought…

    Best Regards,


  4. What happens when an engine blows catastrophically? Presumably all of the oil and debris like bits of shattered valve and broken piston ring that used to exit relatively safely out of the rear exhausts will potentially head straight for the rear tyres with incredibly dangerous conmsequences?

  5. This is a complete misunderstanding of Bernoulli’s principle. The low pressure area occurs WHERE THE CROSS SECTION IS SMALLEST and,as a consequence, the air-flow is quickest.

    Bernoulli’s principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure

  6. Surely you meant to say “decreasing the pressure of the air being forced through between the floor and the ground”. If you are increasing the air between the floor and the ground, you are implicitly decreasing the downforce.

  7. With the exhaust blowing onto the floor from the front, could there not be an increased risk of debris entering the system..? I small off across the gravel could lead to a terminal failure of the exhaust system or even the engine itself……..but hey I am sure they have thought of that !

  8. Take two empty coke cans and place the 1cm apart. Get a straw and blow in the gap. The cans will come together due to the negative pressure created by the airflow. Voila, Venturi effect.

    I wonder if – as an addition – the hot air will help to warm the rear tires too.

  9. D,

    I read the same thing from Ferrari.

    Maybe Ferrari have read Google’s take – down policy? 🙂

    – j

  10. It’s even more confusing when you allow that the Bernoulli “effect” is used to describe keeping disc drive heads floating above the platter, which is rather the opposite of what we’re discussing here, or what is desired by these engineers.

    Equations can have two sides, or lots even.

    Rather better you are a F1 journalist Joe, than, say, an options trader; for the positive outcome I am most genuinely thankful! 🙂

    (believe you me, my head hurts when thinking about these things. The nice thing about physics though is that it can be delightfully simple, and yet be so strange in behavior. Oh, maybe you are a physicist manque, after all!)

    yours in jest,

    – john

    (I must get a proper keyboard for accents)

  11. “there seems to be some advantage gained by using hot air to seal the underside of the car from the external air,”

    Just like the warm air curtains used at the external doors to shops and offices – the warm air helps keep the inside inside, and the outside outside, but it’s much safer than a piece of carbon fibre or rubber rubbing along the ground.

  12. Ironically, it’s Team Lotus who currently have problems with heat damaging parts with a normally blown diffuser.

  13. Very interesting that Mclaren (and it seems here ferrari) may be chatting about it. there have been some engineer moves from McLaren to ferrari recently have there not 😉

    I look forward to seeing how effective it is. The idea of using hot air from the exhaust to create I kind of fluid, aero skirt if brilliant, I love F1!

  14. @Jakub
    There’s no such thing as “negative pressure”, at least not as an absolute. I suppose if you were to take atmospheric as your zero point, then you could say low pressure areas were negative. It’s all about pressure differences really. Highs v.s. lows. In your drinks can example the high is normal atmospheric pressure, the low is the accelerated flow. The cans move together not because they’re pulled by the low, but because they’re pushed inwards by the high harder than they are pushed outwards by the low. Same result, different explanation.

  15. The Venturi effect is created when a fluid is squeezed through a small opening and then expands as it exists.

    After a very spicy home made curry last night I think I am currently producing the Venturi effect.

    Should I patent it?

    Sorry but someone had to post this comment 🙂

  16. This is an interesting concept. My first two thoughts on the were how does pumping corrosive gases through the sidepods damage the car and what affect will those hot gases have on the ability of the cooling system?

    I hadn’t considered the problem with noise or blow ups mentioned by previous commentors. I imagine this modification will be another one season wonder and will be banned for next season. Who really wants teams spending a fortune optimising the shape of sidepods to optimise exhaust gas flows and finding exactly the right spot and angle to site the exhaust exit?

  17. From an old timer, as it were and someone who just abhors the current level of aerodynamic “sophistication”, would anybody out there know the mechanical as opposed to aerodynamic grip percentages?

    Personally, I would ban ALL aerodynamic devices (don’t they look sooo ugly) and let the driver sort it out…

    1. Neil Morrison,

      That would be Henry Birkin. There are various theories. Legend has it that at Tripoli in 1933 Birkin burnt his arm on the exhaust when reaching for his cigarette lighter. However WO Bentley insisted that he was bitten by a mosquito, which triggered the malaria he first contracted during the 1914-1918 war in Palestine. Either way Birkin died of septicaemia despite the best efforts of his former team-mate and eminent bacteriologist Duncan Benjafield.

  18. Great piece, Joe.

    Maybe you could also explain to us the pros & cons of the push/pull-rod types of suspension. From the little I know, the different suspension types affect the way the cars are designed today too.


  19. These exhaust gases are extremely hot,
    surely they would melt the tarmac?

    I’m going to try this out on my Golf GTi

  20. Never mind all this hot air talk. Jumping in a Grand Prix car and driving off in a lounge suit, fantastic. Those were the days. Can’t happen now of course, the lounge suit would not display the appropriate sponsorship at the post race interviews. The most critical part of the whole weekend.

  21. any engineer/designer loves a new set of rules, its a challenge, and I love to see the way these guys rise to it. Its the endless fascination of F1,and thats why we all love it!

  22. Joe,

    Back in the “old days”

    Man….It was only 1979- 1981 when they had those.

    All the best from another “old timer”

  23. Hi Joe.
    As always an informative article.
    When I first heard about it, I didn´t believe it because wíf you look closer at the teaser video from Lotus Renault, the one they released a couple of days before the launch, at 24 seconds into the film, you can clearly see two exhausts right where you suppose they should be; at the back. hey are covered under the engine cover, but they are there. Am I the only one who has seen these? I wrote to Lotus Renault and got no answer. I also wrote to Pitpass and they said they never noticed them before….
    I think it´s more a question of a double exhaust system, than having them only inside the sidepods.
    Would like yor feedback on this.

  24. OK, let’s put this in simple physical terms and let’s make fun speculations – feel free to shoot me down 😉

    1. The counterintuitive bit is that the FASTER THE SPEED of a fluid (such as air), the LOWER ITS PRESSURE: thus, to generate downforce, one needs to increase the speed of air going under the car, so that the pressure below the car (p1) is smaller than the pressure on top of the car (p2): the difference between the two pressures, p2-p1 is the absolute pressure that pushes the car down. (a diffuser is used to increase air speed by facilitating exit of the airflow below the car)
    2. HOT GAS occupies a LARGER VOLUME than COLD GAS at the SAME PRESSURE: thus, as hot air exits the exhausts at the front of the sidepods, it EXPANDS, preventing cold air under the car from escaping from the sides of the car, effectively “squeezing it”, and thus increasing the velocity of the air flow under the car (see point 1).
    3. HOT GAS contains LESS GAS MOLECULES than COLD GAS, at the same pressure. DRAG (friction) is caused by gas molecules interracting with the external surface of the car. Thus, the area of the car shielded from cold external air by a layer of hot gas (the external side of the sidepods in this instance) will have less drag.

  25. @Chris

    Its a long way down this rabbit hole.. I take your point re:negative pressure, indeed I did mean it in relation to atmospheric pressure, but my phrasing was as Mr.Petrov might say ‘not elegant’. I must say though, I did not claim that the lower pressure ‘pulled’ the cans, that’s impossible, at least for now.

  26. “The point of interest (and this is way beyond my technical abilities) is that there seems to be some advantage gained by using hot air to seal the underside of the car from the external air, so that the exhaust air running along the undersides of the floor, makes the cooler air in the centre travel faster and thus create more downforce.”

    I think it’s quite simple – the low pressure air in the centre would draw air in from the sides without a skirt – air drawn in that way reduces the vacuum effect and downforce.
    Exhaust gases are very hot, but cool rapidly and contract as the do so.
    If very hot air (exhaust gas) is blown under the sides of the car, and that is drawn in instead of cold air, it will contract as it cools, reducing pressure.
    Thus the harm to the venturi effect and downforce by sucking in very hot air is much less than that of sucking in cold air, and it may even be more effective than not sucking in anything at all (skirts).

  27. Also of course it is being blown along at great speed from the exhaust and will therefore speed up the air alongside it.

  28. @renato
    Put very simply, the pull rod system allows the arms to be much lower down, where they disrupt the airflow less and give better aero at the rear. The idea is to use a simple L shaped lever that converts the force that would have pushed up on a diagonal damper (classic F1 suspension) and re-direct it so it pulls on a horizontal one instead –
    Hard to picture in words, but imagine a pivot in the angle of the letter L – push up vertically on the short bit and it pulls horizontally on the long bit. Turn it upside down, adjust the lengths are required and you have the up motion of the wheel pulling on a low horizontal damper instead of pushing up on a vertical one like a road car, or one at 45 degrees like the classic F1 design.
    Getting the design right is a bit more complex :-), but that’s the principle.

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