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E92 M3 Race Car Preparation – Bodywork


By Thorney Motorsport – Wed, 03 Mar 2010 12:36

This month is a bit of a work in progress really as a racecars aerodynamics can only really be fine tuned and fettled whilst out oncircuit (sadly we lack the £40m odd needed to run our own wind tunnel, althoughwe do have access to one) so the initial stages of design are developed on thechassis in a static state. The very subject of aerodynamics tend to bring outthe worst in people, everyone happily quotes drag coefficients, down forcelevels and anything else they’ve managed to learn from the internet usuallylosing sight of the one key feature that matters above all else – there is noone feature above all else – aerodynamics and bodywork design has to cater forso many requirements that there is no one single design that can do everything,you have to compromise.

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For the GT3 project we have concentrated on three things –reduction of weight, increase cooling (engine and brakes) and enhancedaerodynamics.

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First up in any race car bodywork development is the frontbumper, what you do here affects the whole car so its development needs to becrucial. The E92 M3 has a relatively simple front bumper design which reflectsthe need to get air into the intake and to keep the gearbox cool, so for therace car development we kept the overall look similar – if it ain’t broke don’tfix it, this means the top part of the bumper is identical to the standardversion only we have also extended the front down by another 85mm. In additionto the extra depth we’ve also added extra brake duct holes to aid cooling tothe brakes, the standard bumper does have these underneath the bumper itselfbut by moving these to the front and expanding their size to 80mm means weshouldn’t have any issues with overheating brakes.

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The underneath of the bumper is also completely different tothe OEM one, the standard bumper is relatively flat then being attached toseparate plastic under trays, with the race version we have integrated theseparate under trays into one unit allowing for a flat floor under the front ofthe car and a rigid fixing to the cars chassis. The underside of the bumper isextended to take a splitter to maximise down force from the front, thissplitter is made of plywood – they are sacrificial items on race cars.

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Best thing about the whole design is that the road versionsare identical so the road upgrade bumper will replicate the benefits of therace bumper.

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The bonnet design was more about getting heat out of theengine and getting rid of weight, the standard bonnet weighs 8 kg’s which isn’tthat bad really but the carbon fibre one weighs 800g, thats a lot of weight tosave especially high up on the chassis so handling will be improved as well. Atthe same time we have been developing a larger airbox for the car so weincreased the size of the hump by 15mm to accommodate that when it goes in (italso looks cool!)

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The bootlid was another weight saving exercise, the standarditem weighs 13kg, the replacement version only 600g, for all the bodywork weuse single skin carbon fibre so its stiff but very light, for road car versionswe use double skinned carbon fibre to give extra strength so we can usestandard hinges and locking mechanisms. The CSL ‘flip’ design was a naturalchoice, the road cars look so much better with this design on.

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Finally we come to the wing. Yes, its big, very very big, infact its as big as we’re allowed under GT racing regulations as for coupe typecars as the M3 is a rear wing is essential to create the down force you need.We use a similar wing on the E46 M3 CSL Cup cars to great effect, we can runfrom 0-13 degrees of rake (the angle of the wing relative to the ground), havethe ability to run a gurney flap (small strip running behind the wing – notshown in the pictures)  and itsvery light (2kg’s) which is important.

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You’ll note a certain vagueness in my comments this month,thats because until we get the car on track we wont know how good or bad someof the bodywork modifications are, we know the bumper is good and there are fewother way we can improve and the boot and bonnet are both exercises in weightand heat really but the wing will take some testing to find the right heightsand angle for optimum performance – low drag/high down force. At this timewe’ll also decide on an exhaust, side exit or rear, side allows the use of afull rear diffuser package but is more expensive and more difficult to make,rear will be heavier but easier but allows us to run a standard fuel tank,decisions decisions.

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