Renault R31 Front Exit Exhausts (FEE) – Explained

Renault have found a new solution to the blown diffuser concept. In fact they’ve turned it on its head. With an exhaust that exits at the front of the sidepods.

Last years teams reintroduced the blown diffuser concept, either by blowing exhaust gasses over the top of the diffuser, or by creating an opening into the diffuser to blow inside the diffuser. Both solutions created more downforce. With the latter solution now banned, it seemed the less effective over-blown solutions are all that’s left to race. However LRGP have found another way, blowing the front edge of the floor.

For a diffuser to create downforce it needs as much flow to pass through the venturi as possible. Teams arrange bargeboards and other aero devices to build up a high pressure region ahead of the floor to ensure the greatest mass flow underneath. Its then down to the expansion ratio of the diffuser to pull that flow through. Last years blown diffusers improved the expansion ratio, but not the flow ahead of the floor. What Renault have done in to lead the exhausts forward through the sidepods (about 1 meter) in-between the chassis and the radiators, then turn the exhaust 90-degrees to point it down towards the leading edge of the floor. The exhausts gasses follow the curved leading edge and round underneath the floor. This accelerates the flow under the floor for more mass flow and hence more downforce.

Problems with this solution are mainly to do with heat and engine mapping. With exhaust temperatures of 6-800c some clever insulation solutions are needed to keep hits heat from the fuel tank, radiators and a electronics. Then the Renault engine team lead by Rob White need to design exhaust tuning to deal with a far longer secondary pipe. typically longer pipes are better for low revs, somewhat contrary to the needs of an engine running at 18000rpm. Renault placed their KERS MGU and Battery underneath eh fuel tank, this was clearly to allow the packaging of the FEE. Unlike the McLaren F-duct, it is possible for this solution to be copied as no monocoque alterations are required.

82 thoughts on “Renault R31 Front Exit Exhausts (FEE) – Explained

    • McLaren will use a similar approach, and Ross Brawn announced they are working on a similar solution right now… so yes, this seems like the way to go.

      1= O ESCAPE DA RBR

      • google tells me this translates to…..

        1 = ESCAPE (Exhausts) RBR

  1. Hi Scarbs,

    Thanks for your usual great insight and analysis!

    Simple question. Do you think all the other teams will be looking to copy this or not?

    • I’m not scarbs, but I’ll try to answer. In my opinion, that would be very hard to do. A lot of these parts are homologated and temperature-sensitive. If this works out well for Renault. It will be a dangerous road to go down for the other teams. They will most likely have much smaller space to fit the exhaust in, and it will be risky regarding cooling. The Renault does have a bit bigger sidepods than the other teams.

      But again, that is just my opinion, I’m nothing close to a designer, or a person with wide knowledge of physics.

      • Not to rain on your parade, but a clue is in the last line of the article :

        Unlike the McLaren F-duct, it is possible for this solution to be copied as no monocoque alterations are required.

      • “ has emerged that McLaren’s 2011 challenger also features a novel exhaust system…”

        “Renault’s thinking is in the right direction,” said team boss Ross Brawn. “We are working on a similar solution.”

        So it looks to me like everyone will try to copy it ASAP, and McLaren and Mercedes are already working on it.

  2. I seem to remember that with the current blown diffuser design that teams would have to heat treat or somehow strengthen some rear components to withstand the heat produced by the exhaust gases.

    Would putting the exhaust further forward allow the exhaust gases enough time to mix with the rushing air and cool enough that this wouldn’t be a problem?

    Oh, and keep up the good work. I love all this technical stuff 🙂


  3. Isn’t this solution a little bit dangerous on side crashes?

    The pipes will be much more closer to the driver creating an tremendous heat zone, plus fuel and oil you have a fireball.

    Remember Kova’s Lotus last year, if the same problem happens to this concept, isn’t going to fire up pilot’s face, since the fuel will flow to front, get wind and back up and down the car?

    Ok, Kubica it’s a tuff guy, and Petrov is russian. I think they won’t care about it.


  4. Call that going to the edge of innovativeness. If they get it to work without overheating, that might be the trend.

    As with the EDB i expect teams to have their work cut out to fit it in without torching their cars, then make the flow work and get the engine retuned. Not impossible, but we will see some sore heads (or bums?) before anyone successfully copies this.

    • Well it does live in the side pods, which is the biggest airflow inlet in the car, so perhaps that help keep it cool. In which case, the pit stops could be interesting with a stationary car, or the grid for that matter, safety car… Anything that stops the high volume of air cooling it down

  5. Isn’t there the possibility of the energised airflow spilling out of the side of the car? Surely energising the diffuser area is better as it then draws all the air out from under the car anyway? Plus you’re then controlling and tuning the air flow through the diffuser itself, rather than just energising the air further up and hoping the diffuser captures some of it?

    Nice idea sure, but I think it’s going to cause more than a few problems…

    • RR, I was thinking that having those very wide and flat openings so near the diffuser top might allow a very nicely controlled and slightly energized flow. But I also don’t know if that even makes sense, aerodynamically.

  6. Wow. If this works it’s easily as impressive, if not even a bit more so than the F-duct or EBD in my opinion. Let’s hope the Renault’s don’t start blowing up during long stints first though!

  7. Only future tests will show whether this will be of benefit or not. I see, just as others do, a problem with heat, but I don’t believe that engineers with Renault haven’t thought of that. Let’s wait and see.

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  10. Scarbs, fantastic as always but can you please clarify the last sentence…

    “Unlike the McLaren F-duct, it is possible for this solution to be copied as no monocoque alterations are required.”

    The McLaren f-duct was copied to one extent or another but you dont think the Renault FEE, if it is an advantage, will require any monocoque alteration?



    • I was thinking the same. If it does prove to be as beneficial as it is innovative, then the other teams will definitely have their work cut out implementing it without altering the tub/monocoque. Plus, I think someone else mentioned this as well, the R31 looks to have bigger sidepods/inlets than the other teams – this could be an issue as well.

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    • Yes the potential for a thermal event is quite high I would guess. Also shirley the back pressure on the exhaust will vary with the car’s air speed, thus affecting the tuned nodes of the air column in the exhaust.
      Still this could help the real Team Lotus since not having a fire is usually good.

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  14. Блять вы заебали тут писать не по русски! Ну ка на хуй перестроились быстро. А то я вас не хуя не понимаю!

    P.S. : Виталя лучший!!!

  15. Thanks for confirming this Scarbs. I was trying to think more about the physics going on here…

    Do you think that the warm exhaust gas (once it has cleared the high pressure in the pipes) might even reduce the low pressure under the floor as it is hot?

    Also, all that hot air should do a great job of energising the boundary layer on the top of the diffuser, improving its efficiency.

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  18. Hi Scarbs 🙂

    A couple of questions from my side.

    Do the regulations restrict the diameters of the primaries and secondaries? If not, couldn’t they simply have bigger diameter pipes (than usual) to reverse the effect of longer secondaries to push the effective peak of these pipes towards high revs? My knowledge in building headers is nothing impressive, so apologies if my question is stupid.

    Secondly, how much effect would the direction of the exhaust have on the exhaust back-pressure. I cannot make out the angle of the exhaust bend at the end, but it surely isn’t perpendicular to the road surface. Unless there is something deflecting air away from the exhaust in front of the pipes, this would simply kill the scavenging effect that these guys rely upon to build their headers.

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  20. Looks like a very ingenious solution.

    However I do wonder about possible downsides of having the exhaust pipes pointing forwards into a potentially 200mph airstream:

    Will the exhaust gasses be able to exit efficiently without affecting engine performance, or will the airflow push any of those gasses back into the exhaust?

    Also, will the exhaust gasses create a ‘forward-facing thrust’ effect, slowing the car down (however slightly) via Newton’s third law?

    • I’m going to assume there’s a one way valve in place here but I would think a trip through a gravel trap could be very detrimental

  21. Does anyone know how much time this development could be worth? Taking a stab in the dark if I had to guess I would say maybe half a second? Because that was the gain from EBD last year.

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  23. Scarbs – thanks for the insights!

    Can’t wait to see the pitlane and starting grid equipment that goes with these “exhaust outlets where the driver’s bottom is.”

    They’re going to need something to deflect the exhaust gases away from the driver, the engineers leaning over the cockpit and the radiator inlets.

    Presumably, “alternate pipes” wherein there are two possible exhaust outlets, the front one working only at “aerodynamic speeds” are not kosher.

    Hell of a CFD problem, though! Tune exhaust pipes such that gases flow from one outlet up to X km/h, and out another above, contained within the available space. There’s an engineering meeting …

  24. Based on the leroy photo it looks to me like the the outlet is facing backwards, about 40degrees off the centreline facing the leading edge of the floor. You can see a reinforcing plate fixed to the edge of the floor.

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  26. I believe it works in another way…if you blow air underneath the car, you won`t have much effect ( in my opinion) because actually you need low air pressures in order to produce downforce. Former blown diffusors worked by accelerating the air where volume was increased, and airspeed reduced. So by blowing in at THAT point helps you do increase downforce by higher airspeeds which, as Mr Bernoulli could tell is the result of an increasing volume. I Believe that this Renault thing works slightliy different. It helps shutting the open sides of the car`s floor, and at the very end, or the beginning of the diffusor they manage to lead those controlled turbulences ( which are more energetic than clean air) into the diffusor. I am not a pro but very interested, so would you think this was right?

    Greetings from Germany, the country of next years winning team 😀

    • Exactly, from what I have read elsewhere that is what quite a few people are thinking. They act as a kind of Fluid, aero ‘skirt’ as in the old days of ground-effect. They not only separate the airflow from the airflow to the sides of the car floor, they also make it cleaner as it leaves exits the diffuser.

  27. There’s some cool science here …

    Fun fact: An NHRA dragster develops 600lbs of downforce from it’s upturned exhausts at full throttle.

    This new Renault has them pointing DOWN. The Aero Boffins must really like their numbers to pull this stunt.

    Let’s look at them …

    An F1 exhaust cannot be worth 600lbs. Dragsters run on nitromethane which has 8 times the explosive capacity of gasoline. F1 exhaust must be a number closer to 60lbs then.

    Renault is then proposing – dependent on throttle position – there will be from zero to sixty pounds of uplift ahead of the car’s centers of gravity and aero pressure. The further ahead of center, the greater leverage the exhaust flow has on car balance.

    Let’s imagine such an effect along with Kubica and Petrov through the not-quite-flat Maggots/Becketts Complex … in car’s which, at the limit, need only the force equivalent of a single finger to tip them into a spin … the contra-flow with the airstream making it a whole different kettle of fish from the variable downforce problem presented by rear facing exhausts …

    Unless, they really do point FORWARDS. This solves the contra-flow problem.

    Nor, as you might at first think, is it a problem to have outlets facing into the incoming airflow. The flow differential is no contest in favor of the outgoing hot exhaust gases at 800 liters/sec. (Math: 300 revs/sec x 2.64 liters = 792 l/sec.) Blowtorch in a breeze … even at 320kph.

    The drag penalty is almost zero because the forward facing pipe is always pressurized, blocking incoming flow (as in: trying to fill an already full cup – the incoming flow is blocked.)

    You still have to account for the hot exhaust gases being channeled underneath the sidepods. Thermal convection and radiator inflow draft would seem to naturally pull the stream upwards.

    Unless, the flow energizes not the underside flow, but the sidepod undercut flow. Acting outwards, not down. This would make it primarily a drag reduction trick, not a downforce production trick.

    In which case: Yeah baby, please cut my drag at full throttle!

    Conundrums like these is why the Aero Boffins use the fastest computers in captivity to back up what otherwise would be wild-ass guesses. (Behold the proto-singularity! 😉

    We’ll find out as testing unfolds.

    … and there’s your cool science.

    To try at home: (Worth the bother 😉

    If you care to feel a “variable downforce effect” with you own fingertips, do the following experiment. No super-computer required.

    Go to your kitchen.

    Take an ordinary teaspoon (you know, one conveniently shaped like an upturned wing when viewed in profile 😉

    At the sink, run the tap.

    Holding the handle between thumb and forefinger, slowly move the spoon bottom toward the waterflow.

    When the bottom hits the flow, you’ll feel the spoon be sucked in.

    Magically, you’ll have downforce at your fingertips. If you bob the the spoon bottom in the flow you’ll feel the “downforce” vary. If you just let it hang, pulled in by the flow interaction alone, you’ll feel a fluid finding it’s own equilibrium.

    Extra credit: Take a moment to feel the lift-to-drag ratio of your teaspoon. It’s the difference between the pull-down of the waterflow and the pull-in to the waterflow on the spoon. If you feel compelled to try every spoon in the house, looking for the best lift-to-drag ratio, you have a taste of what motivates an aero boffin.

      • Absolutely. And as a result, the flow does not get deflected undearneath, I think, but goes on top of the border sections of the floor. My wild guess as a non-aerodynamicist is, judging by the shape of the floor, that a part of the flow just runs away to the left and the right of the car, and – IF the floor is cleverly designed – a small part of it goes all the way to the back, warming up the tyres slightly.

        If this works, it’ll be know as a work of a genius.
        BUT – either way, the exhaust definitely points backwards.

      • Sorry, wrong. It’s Scarbs who says they point down. I’m saying I can only see it working if they point out the sides.

        The photo here has half the exhaust exit blocked by bodywork. The photo at, not only shows that the exhaust exit points outwards at 90 degrees to the chassis, but has caught the curve of the sidepod underside directing this flow around the undercut corner.

        Nobody outside Renault really knows how it’s intended to work. Some good exhaust plume photos should show what’s truly different from the other cars.

    • You left out a few more assumptions. Even if the exhaust was blowing straight down, it wouldn’t provide 60 lbs of lift.

      A few discrepancies:

      1) Dragsters have 7000 bhp, F1 has 750 bhp.

      2) Dragsters have 8.2 litre engines, F1 has 2.4.

      3) Under full throttle, a dragster engine consumes 5.7 litres of nitromethane per second, which is a considerably higher mass-flow than F1.

      4) Dragsters are supercharged to 4-5 bar (up to 70 PSI) of boost.

      I have no clue how each of those variables would affect the pressure at the exhaust exit, but a wild guess would make me think that a dragster would be closer to 100 times the exhaust force than the 10 times that you assume. 6 lbs of lift would be easy to overcome by blowing the entire underside of the car.

      The fact remains that the more fluid you can force under the floor, the more it will accelerate and generate more downforce. That is why a few teams ran lift-inducing wings ahead of the sidepod to direct more air under the flat-bottom, up to 10-15 years ago. Little loss for a big gain.

      • “I have no clue how each of those variables would affect the pressure at the exhaust exit …”

        Right, because they don’t. Here’s my back of the envelope: An NHRA engine is 3x bigger in displacement, but spins at 1/2 the revs with a fuel that’s 8x more combustive. In round numbers that’s a reduction of 10x. It’s the volume of gases moved, not the horsepower produced or the fuel flow which is at issue here.

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  30. Someone on another site identified some parts the RB7 and R31 have in common that the others haven’t, they speculated that RB already had the FEE but were leaving it off the car at the moment.
    I am expecting McLaren to have an interesting exhaust outlet too, no evidence, just a hunch.

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  35. Nice articles, but they’d be even nicer if you could find three extra minutes to do some proof-reading. The numerous typos are distracting.

    • I appreciate its a distraction. Let me explain: I worked out the RB7 exhaust at about 11pm last night, after a full day at work, one and half hours on Peter Windsors webcast, I sat down drew the two pictures and typed up the analysis in about 30-40 minutes. I’d rather push the info out quickly and return to edit it, than delay things.
      My weakness is fast accurate typing, but I edited the typos about 30 minutes after posting the blog

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  39. Hm, sharp … but I don’t think they are trying to move the exhaust air under the car, to me it looks like they are trying to blow it down the side of the car.

    Looks like they’re trying to make an air curtain, like the old front end-plates did back in the early 90s.

    It’s side skirts without the skirts.

  40. couple thoughts:

    adding hot air under the car will rapidly cool reducing pressure, also displacing cool air that would normally enter from the front of the car.

    running a “blanket” of hot air over the leading surfaces of a fast moving object reminds me of super-cavitating torpedos. they eject a small stream of exhaust gases out the front of the torpedo to create a gas bubble in front, greatly reducing drag and allowing much faster travel through an otherwise very thick cold fluid.

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