Rossins Posted July 21, 2015 Share Posted July 21, 2015 Morning, Thinking about adding a rear diffuser to my car & interested on other drivers experiences - do they make any difference and any recommendations for a particular type. Thanks in advance. Cheers Simon Quote Link to comment Share on other sites More sharing options...
B.RAD Posted July 21, 2015 Share Posted July 21, 2015 Hi Simon, great to meet you last weekend! Thanks for the battle I've got an aerodynamix one with the full fitting kit if of any interest? In terms of usefulness, hard to say but I'm concerned that unless you have a full flat floor & sealed gearbox tunnel at the engine bay end, all it does is create a big air trap at the back. If you have a look at the curborough pictures thread from last year, there's a photo I took of Marks awesome car down the final straight - the diffuser is pushed down suggesting the airflow is above, not below it. At the mo it feels like just more weight than anything directly useful, so I haven't used it. Quote Link to comment Share on other sites More sharing options...
Terry Everall Posted July 21, 2015 Share Posted July 21, 2015 A rear diffuser keeps some of the dirt and wet off rear and stops some of the air entering he "boot area" which can act like a parachute. 1 Quote Link to comment Share on other sites More sharing options...
tkm_dave Posted July 21, 2015 Share Posted July 21, 2015 As Terry says, they're good for keeping stuff a little dry and cleaner, reduces the 'parachute affect' in that area too. Also helps reduce drag slightly if they are the correct angle from the floor. Common misconception (by me included until fairly recently) is that they produce some downforce. They don't they just clean up the way the air flow exits the back of the car, which in theory helps reduce drag. Whether you'd notice any performance benefits other than the extra weight saved from clean diff/wishbones and looking kinda cool is debateable though! Quote Link to comment Share on other sites More sharing options...
B.RAD Posted July 21, 2015 Share Posted July 21, 2015 This is the link to the photos, its the orange car that is only half in shot - it was quick! Look closely at the rear diffuser... http://s469.photobucket.com/user/barnyf_photo/slideshow/ From my limited knowledge, and I'm happy to be proven wrong, the above benefits only apply if you have a fully flat floor (like an Elise) with the gearbox tunnel sealed, otherwise the airflow is still heading straight down the transmission tunnel and into the rear panel, but without the open underneath to escape. Holes in the rear panel might have more benefit. Christian trialled times with the diffuser on and off at Blyton last year and he was quicker without it. Read into that what you will, but bear in mind we're novices & practice/experience will likely give us more time than aerodynamic tweeks. Quote Link to comment Share on other sites More sharing options...
AdamR Posted July 21, 2015 Share Posted July 21, 2015 Christian trialled times with the diffuser on and off at Blyton last year and he was quicker without it. Interesting. Would love to know more details around that - any differences in weather, if it was first or second run, how well he knows the track, how much difference there was, exactly which diffuser it is, etc! Quote Link to comment Share on other sites More sharing options...
tkm_dave Posted July 21, 2015 Share Posted July 21, 2015 BCF, very good point about the transmission tunnel! That could make a noticable difference to keeping dirt and spray out of the rear end area, though closing up the gaps around the diff where it sits slightly inside the transmission tunnel could help for fairly little effort/cost. 1 Quote Link to comment Share on other sites More sharing options...
pickmaster Andy Lowe Posted July 21, 2015 Share Posted July 21, 2015 1 Quote Link to comment Share on other sites More sharing options...
AdamR Posted July 21, 2015 Share Posted July 21, 2015 I'm quite sure it does - that's exactly how I've got mine fitted Quote Link to comment Share on other sites More sharing options...
B.RAD Posted July 21, 2015 Share Posted July 21, 2015 Interesting. Would love to know more details around that - any differences in weather, if it was first or second run, how well he knows the track, how much difference there was, exactly which diffuser it is, etc! I was sort of trying to caveat this by pointing out that both Christian and I are novices, therefore it's hard to justify improvements in time by car changes, when it is just as likely delivered through a better line or better corner entry/exit speed and nothing to do with car adornments! However, these are Christian's times from last year - if i remember correctly, he removed the diffuser after T1 on Saturday: Sat- dry, clear and hot P1 82.24 P2 77.60 T1 76.20 T2 74.94 T3 75.19 Sun - dry, overcast P1 78.69 P2 74.76 T1 97.55 (spin) T2 75.30 I don't know enough about the aerodynamics of the Westfield to put scientific evidence behind this, all I know is that as Dave says, a diffuser is about smoothing airflow underneath the vehicle, not creating downforce, and in order for that to happen the pathway for the air under the vehicle needs to be smooth and unobstructed, with the correct elevation on the diffuser at the right point on the vehicle, with sufficient extension beyond the rear of the car to move the air out of the turbulence created at the rear of the vehicle. It also needs to avoid any air force on top of the diffuser, which unfortunately the open transimission tunnel creates. So for me, and its only my personal opinion, I don't believe that sufficient thought or testing has been put into the current range of diffusers available for our cars to make any difference, therefore in the effort to reduce additional weight I have opted not to use one. However, tkm_Dave's car has much more 'track tested' aerodynamics fitted, including IIRC a flat floor from nosecone back, so he might be able to offer a real world comparison. Pickmaster's concept is also an interesting one, but again depends upon the extension of the diffuser from the rear of the vehicle (I seem to recall around 5" being considered the minimum, more research required there). A much more complex response than you may have been expecting Simon, but hope it helps your thought process!! Quote Link to comment Share on other sites More sharing options...
lewis Posted July 21, 2015 Share Posted July 21, 2015 So why don't people seal the transmission tunnel? It doesn't seem *that* hard to do? Or it more to do with regs? I'm still new to this, hoping to have the car pass IVA tomorrow and one of my post IVA tasks is to fit an Aerodynamix rear diffuser. Quote Link to comment Share on other sites More sharing options...
AdamR Posted July 21, 2015 Share Posted July 21, 2015 Good post Barny, a few bits to think about there! I don't think the diffuser has made a difference in Christian's case, there is a general tendency towards improvement with track familiarity I think (also demonstrated by lap time dropping back off for the first run on Sunday). As an extra point, when the front of mine wasn't fixed firmly enough at the front lip and it actually got pulled down to the floor at about 55mph the first time I fitted it - so it must be producing some sort of downwards load somewhere. The first and only time I've used it on track was at Blyton, and through Port Froid the car was horribly understeery (more so than I remember) - the high speed balance was completely different to low speed, maybe indicating some sort of rear downforce? This may have been down to something else though, as you said it's really hard to say for sure. Too many maybes! Lewis - I think it's to do with getting rid of hot air from the engine bay... Quote Link to comment Share on other sites More sharing options...
John Loudon - Sponsorship Liaison Posted July 21, 2015 Share Posted July 21, 2015 Just a diffuser is no use on its own other for looks and cleanliness. However, consider the whole of the underside of the car covered including engine bay and transmission tunnel plus a diffuser Quote Link to comment Share on other sites More sharing options...
FILFAN Posted July 21, 2015 Share Posted July 21, 2015 thought this page was about making a nice cuppa tea 1 Quote Link to comment Share on other sites More sharing options...
msisleman Posted July 21, 2015 Share Posted July 21, 2015 Just a diffuser is no use on its own other for looks and cleanliness. However, consider the whole of the underside of the car covered including engine bay and transmission tunnel plus a diffuser I've also been thinking about a diffuser and whether to (re)fit my PlaysKool one or not..... I have a fully flat floor from nose cone to where the diffuser would be, but I had my diffuser half come off on track. Granted, the previous owner hadn't done the best job at attaching it with only rivets, however I can't help but think there may be a positive pressure build up in the boot area with no good way for it to escape. Even with a fully flat floor - the air enters through the nose cone/rad and then essentially has no where to go apart from all the way down the car into the boot area? Maybe I should consider some engine bay venting for this? Quote Link to comment Share on other sites More sharing options...
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