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29 Jun 2012

I talked briefly about Red Bull's apparent usage of 'Off Throttle' blowing in Valencia (although they have been doing this since the start of the season) in the latest edition of the #TechF1Show. In my previous articles I looked at the aerodynamic gains Red Bull had taken at Valencia when the team finally got the Sidepod Tunnel to work: this leads us back to the topic of Throttle Blowing which helps to maintain a continuous exhaust flow over the vital aerodynamic components at the rear of the car.

My theory leads me to believe that Red Bull are utilising cylinder deactivation in order to attain a continuous exhaust flow which in turn leads to more downforce and better overall balance. The advantage of using exhaust gas whilst off throttle can be huge in terms of aerodynamic influence, utilising exhaust gas whilst cornering stabilizes the car and gives a continuous airflow to the key aerodynamic elements at the rear of the car.

The video above highlights the 'Off Throttle' sound of the RB8 at Valencia. 

The FIA's amendments to the rules for 2012 were designed to stop the teams running their exhaust solutions internally giving them the maximum area of coverage above the diffuser. As always the teams have engineered ways to continue using the exhaust effect to gain rear end downforce.  The more difficult aspect however has been losing the effect of 'Off Throttle Blowing'.  During the 2011 season you will have become accustomed to the in corner 'cackle' sound the cars produced. What this sound was a sign of was the blown effect generated by the exhaust continuing to be used even when the driver was off throttle. To achieve this effect the ECU would cut the ignition but continue to send more fuel to be exhausted during the off throttle moment creating blow through. This continued the blowing effect even when the driver was fully lifted out of the throttle giving a seamless/continuous amount of rear downforce from the exhaust gasses exiting above the diffuser.
The FIA redefined many of the protocols available for mapping the ECU during the off throttle period and so many are now wondering how Red Bull are achieving the effect. Red Bull are not on their own in the search for the off throttle effect and all the teams are pushing the boundaries of the new regulations placed upon them. However I believe that Red Bull are utilising Cylinder Deactivation during part throttle in order to attain the continuous blowing effect. Cylinder Deactivation is a process that the teams normally use in Safety Car periods in order to save fuel, this is controlled by movement in the camshafts and can probably be best visualized by watching this short video:

Thanks to the Audi video above we can see how cylinder deactivation can be utilized in different driving conditions

This will allow the driver to stay at part throttle where as previously he would be off throttle, as when using cylinder deactivation it's like driving a vehicle with a smaller displacement engine. This will effectively give better driveability and traction at lower rpm's allowing the driver to stay partly on throttle giving a continuous exhaust plume. This creates downforce irrespective of throttle position (except at possible absolute zero) which in turn gives the driver more balance.  The sound generated is simply a byproduct of deactivating those cylinders. This will help Red Bull achieve more downforce without the loss of the sealing effect at the diffuser. This is important due to the impact of tyre squirt and it's lateral flow into the diffuser channel, removing Tyre Squirt from influencing the diffuser aerodynamically will result in less movement at the rear of the car.  Although the theory is the same as the term EBD or Exhaust Blown Diffuser it can't be held in the same regard as it's effect is not as great.  We shall perhaps have to coin a new term along the lines of CDBD (Cylinder Deactivated Blown Diffuser) although I'm sure someone will come up with a more apt acronym. 

Combining all of these elements (Cylinder Deactivation, Exhaust position, Exhaust plume trailing path and Diffuser design) results in better balance, faster lap times and less tyre degradation. Either the FIA will have to clarify it's position on the usage of cylinder deactivation during racing conditions or we will see all of the teams using the method. As usually occurs in these situations one engine manufacturer's ability to control/benefit from this will far outweigh anothers and so I’m sure we will see a protracted battle to utilise or ban it's use.

Lastly I'd like to leave you with Sebastian's onboard lap, we can see from this how smoothly his transitions between on and off throttle are how much quicker he is able to pick the throttle up.



  1. Why would a smaller displacement engine give more exhaust gas flow? I'm not sure that is correct.

    1. The additional gas flow is available because the RB8 can stay on throttle (Part throttle) through the usage of CD. Meaning it can generate airflow that a V8 couldn't.

  2. That Renault are cutting the cylinders has been known from the start of the season, it was challenged by Mercedes I believe, and upheld as legal by the FIA.

    1. Indeed it was, the FIA know what Red Bull are upto and to change the rules will be incredibly intricate. I think the Renault engine may be more flexible in this department over say the Mercedes & Ferrari engines.

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  4. Hi Matt, some of your assumptions are simply not correct:

    "However I believe that Red Bull are utilising Cylinder Deactivation during part throttle in order to attain the continuous blowing effect."

    -> Cylinder Deactivation is not permitted during part throttle, since that would have the effect of a traction control. Cylinder deactivation (up to 4 cylinders) is allowed only on engine overrun.

    "Cylinder Deactivation is a process that the teams normally use in Safety Car periods in order to save fuel, this is controlled by movement in the camshafts and can probably be best visualized by watching this short video:"

    -> Teams do not always try to save fuel during the SC period, they are actually trying to burn the unnecessary fuel, depending on the overall strategy.

    So generally they do deactivate the cylinders, but not as you described it. The sound comes from EBD and you can hear it while the car is braking.

    1. But the theory still stands, surely? EBD off-throttle (i.e. with no throttle command) is still beneficial; if the driver commands any throttle > 0 then there is a fuel demand anyway, so the gas flow remains, cylinders are no longer cut and thus the requirement for it to not effect traction control is adhered to.

      I'm not sure how downchanges (and their throttle requests) figure into this but as theories go it sounds pretty credible.

    2. Before i answer the first paragraph can i ask if your reference to CD only being available on engine overrun relates to the following articles?:

      5.6.5 The idle speed control target may not exceed 5000rpm
      5.6.6 Except when anti stall or idle speed control are active, ignition base offsets may only be applied above 80% throttle and 15000rpm and for the sole purpose of reducing cylinder pressure for reliability

      The Safety Car statement was made as a sweeping generalization for those not used to the intracrasies of systems used within F1 engines. We have to remember that not everyone has a full technical background in the sport and so sometimes I will make these types of generalizations in order to assist the casual fan.

  5. It was my understanding, that part of the primary reason for cylinder deactivation was reduction in stress on the tire during the braking phase.

    In part from a reduction in engine torque and power pulses being transferred into the carcass of the tire that could accelerate wear.
    And to reduce any of that generated engine torque and power pulses from reducing the effectiveness of the brakes themselves.
    And also because it can allow for a more linear KERS harvesting. Which not only means better charge, but a more consistent and calculable brake force reduction from the KERS system itself.

    All of that means the tire goes through fewer conflicting dynamics, and that can greatly improve tire wear, and reduce degradation.

    Im sure there is some benefit in the form of EBD performance. But it has always been my understanding that cylinder deactivation was purely a way of managing tire wear first and foremost. As it has been for most other forms of motorsport. MotoGP specifically comes to mind.

  6. Good debate guys. Anyone visit Silverstone at the weekend to checkout whether Renault RS27 powered cars were running CDBD (or similar)? Could not distinguish on my TV or was it masked by the forced use of "wet" maps. Eitherway, if any team has the nous to successfully apply an in-house developed control system, in a legal way, then it is up to the other teams to catch up or surpass. Game on.

  7. wow i love the work ..Part Throttle Exhaust Blowing via Cylinder Deactivation technique is awesome


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