EFA Posted April 16, 2004 Share Posted April 16, 2004 Well Count has already stated his airbox provides improved performance to his car, and the couple of runs K2 RUM has had ahve revealed that the flatspot I was trying to eliminate at 125mph has now dissapeared. So imagine to my delight my joy when I find the results of a test I had someone perform at a windtunnel at the ex Activa factory: We calculated that at 8000rpm @ full throttle my car draws 295cu/ft/min of air assuming 100% cyl fill. The airbox was placed in the tunnel, with filter fitted and an evacuation source placed evenly across the four induction ports and set to draw 295cy/ft/min form the box. A barometric sensor was placed in the back of the airvbox with the wind tunnel powered down, and then the tunnel run at 30,60,90mph wind speeds (it doesn't go any faster than 90mph) The results are as follows: No windstream - 0.732 bar 30mph windstream - 0.754 bar 60mph windstream - 0.779 bar 90mph windstream - 0.804 bar So proof indeed that a rudimentry test gives the results I predicted. It may not be turbo levels of boost, but it certainly helps...... Fat Arn Slay the K. Link to comment Share on other sites More sharing options...
Bob Corb Posted April 16, 2004 Share Posted April 16, 2004 Where did the .27 bar depression come from? The .07Bar improvement at speed sounds reasonable but I cant understand why the starting pressure is so low. A good airbox on something like a Honda S2000 or BMW M3 is only a couple of kPa (0.02 Bar) even a bad airbox on an old MGF was no worse than 8kPa. I would have expected that the pressure behind a large foam filter like yours at max power would be about 0.98/99 Bar (i.e. 0.02 below atmospheric of 1.01bar) How much drag did the airbox cause? Sometimes you need to be careful that the power increase isn't wasted on increased drag. Bob Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted April 16, 2004 Share Posted April 16, 2004 1PSI of RAM air at 90MPH....mmmm Significant. You get a higher pressure build up at the base of the screen. Link to comment Share on other sites More sharing options...
StewartG Posted April 16, 2004 Share Posted April 16, 2004 Was this measured with clean air going into the airbox or in the real life low pressure area behind the headlight? Link to comment Share on other sites More sharing options...
Chris G Posted April 16, 2004 Share Posted April 16, 2004 1psi in clean airflow, it's possible that the high pressure created by the nose ups that even more. OTOH if the headlight is sat in front of it bang go all the gains. In my case 1psi was worth 18bhp and my inlet is *behind* the rad so there's an awful lot of gain to be had but I couldn't bear everyone pointing and laughing at it. As bill says puting a scoop at the base of the screen should be the best of all. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted April 16, 2004 Share Posted April 16, 2004 Base of what screen? Have you seen K2RUM. Link to comment Share on other sites More sharing options...
greenpeace Posted April 16, 2004 Share Posted April 16, 2004 Sorry, I still cannot see how this 1PSI increase could be achieved Surely the cab of the recovery truck would hamper the airflow Looking after your environment - whether you like it or not! Link to comment Share on other sites More sharing options...
Peter T Posted April 16, 2004 Share Posted April 16, 2004 Arnie, the only results that i am interested in are real road figures, not theoretical calculationts What your car draws and what comes in the air box are two critical factors in the science of good airbox design Still it should keep noise down 😬 😬 Support the 7 Society...... Ehhh? Link to comment Share on other sites More sharing options...
Slipper man Posted April 16, 2004 Share Posted April 16, 2004 Keep the noise down?! If it works, it will still be drowned out by the noise its owner makes Link to comment Share on other sites More sharing options...
scooby dooby doo Posted April 16, 2004 Share Posted April 16, 2004 I think that Drag force is: F = air density x speed squared x drag coeff x Area / 2 Power is that times speed: P = Fv = air density x speed cubed x drag coeff x Area / 2 Assuming the drag coeef of the box is 1 and that its a 10cm x 10cm we get: (the units are m/s for speed and metres for area) P = 1.3 x 40 x 40 x 40 x 1 x 0.001 P = 83 W P = 0.11 bhp drag at 90mph Does that look sane to everybody 🤔 So the air converts air speed into a pressure gain with neglible drag. I'm still interested in the effects of the headlight and Bob's question about why its dropping so much pressure compared to atmospheric... HOOPY R706KGU Hoopylight R Link to comment Share on other sites More sharing options...
EFA Posted April 17, 2004 Author Share Posted April 17, 2004 Bob, The pressure drop I think is due to the confined space instead of the free air on the open side of the filter. I think 295cu/ft/mi evac is also quite a high value. The pressure drop is also proportional to a reduction in drag I would imagine. The headlamp does not obscure the inlet on my car. Peter, its not really possible to get real road figures as I do not kjnow where there is a full sized wind tunnel with a rolling road or dyno inside. As it was this was done at a former F1 facility. If people wish to point and laugh at it then that is their perogative, however, if it does add 20 or 30bhp to the engines output I too shall be laughing. Its rather looking like that could be the case...... Fat Arn Slay the K. Link to comment Share on other sites More sharing options...
paul jacobs Posted April 17, 2004 Share Posted April 17, 2004 20 or 30 bhp, that quite a gain. Could an engine in a much lower state of tune, like a standard K, expect a comensurate gain with the airbox? Paul J. - Now with a working Seven, facing SVA on Fri 23rd April 04! Link to comment Share on other sites More sharing options...
Mole Posted April 17, 2004 Share Posted April 17, 2004 No Paul - don't do it 😬 SV 52 CAT - moles fly - here Link to comment Share on other sites More sharing options...
StewartG Posted April 17, 2004 Share Posted April 17, 2004 Keith, isn't that comment a little defamatory? There's a lot of time and effort gone into the design of that airbox so why not let him post about it. Link to comment Share on other sites More sharing options...
edmandsd Posted April 17, 2004 Share Posted April 17, 2004 I'd be very surprised to see a tangible benefit at no more than 90mph as would anyone who has ever studied ram air effect. If any benefits are to be had they will be much closer to your max speed and even then they will be marginal meaning you'll have little opportunity to really appreciate the gains. The benefit of your airbox will be the cold air feed and it is this that you need to ensure exceeds the drag losses associated with such a large box. Home of HTR700 Link to comment Share on other sites More sharing options...
Jason Plato Posted April 17, 2004 Share Posted April 17, 2004 How do you intend compensating the ECU map for the ram effect Arnie ? Will you be running a manometer (?) I guess the MOTEC ECU you are running has a facility for compensation ? Not a piss take - just interested Stewart - I'm sure Arnie has a second airbox for his mouth 😬 Dave Link to comment Share on other sites More sharing options...
caterhamnut Posted April 17, 2004 Share Posted April 17, 2004 I dream of being able to experience a flat spot at 125mph 😬 'My First Race - SPA' pictures here 60,000miles in 3years Link to comment Share on other sites More sharing options...
EFA Posted April 17, 2004 Author Share Posted April 17, 2004 Dave (J) Yes the car has barometric compensation whihc will be mapped in using the differential lambda values once the engine is properly mapped static. (i.e. not in moving car). I will speak to the wind tunnel guys on Monday as I do seem to remember saying you do not get a 1.0bar reading in the tunnel due to some stuff they do in order to simulate the kind of speeds an F1 car can travel at..... The important thing to note is the differentiation in the values which proves beyond doubt that you will get more air/ful mix into the engine using the airbox. Whether this is totally offset by the drag is not something I can find out without making a 1/3 scale replica of both car and airbox - not likley to do this....... Fat Arn Slay the K. Link to comment Share on other sites More sharing options...
Bill Shurvinton Posted April 17, 2004 Share Posted April 17, 2004 'The important thing to note is the differentiation in the values which proves beyond doubt that you will get more air/ful mix into the engine using the airbox' dP/dT is differentiation. What fsking good is that to you? I am sorry, using a laminar flow windtunnel test to show that your airbox works in a turbulent flow situation behind a headlamp is at best poor science. If you look at the ram air gains of F1, they were less that the 1PSI you claimed. So either your airbox is better than F1 designers can manage, or you test is flawed Link to comment Share on other sites More sharing options...
Simos Posted April 17, 2004 Share Posted April 17, 2004 F1 is governed by rather large real-life drag issues. I'm sure F1 cold have got massive ram air if they'd stuck a huge funnel above the drivers head. I'm also sure that would have destroyed their top end at 180mph and that they did some serious experiments that gave them the ram they wanted for the drag they were prepared to pay. I recall the air intakes of the old Marches looking like they belonged on the QE2 or K2RUM whereas modern cars are very understated and clearly governed by the aero package. I don't see how having a scoop stuck up above the bonnet that most people could stick their heads into (not Arnie obviously) can possibly be detrimental over a foam filter that just pokes out of the bonnet. I would point out how sh4gged my old Intercon-A kart was if you left the airbox off and that did not even have (was forbidden) an entry in the airstream. Ok Arnie posting figures into this forum is asking for it, but as an illustration of a theoretical advantage it is at least useful and he has pointed out most of the shortfalls of the test beforehand. I don't think he meant differentiation in the integration sense Bill :-) Link to comment Share on other sites More sharing options...
edmandsd Posted April 17, 2004 Share Posted April 17, 2004 I recall reading recently that Ferrari have invested millions in developing an engine dyno within a wind tunnel so they can maximise the benefit of ram air amongst other things. Ferrari quoted a 50 bhp gain or c 5%. This will be at maximum speed of c 180mph (and probably rounded up for the benfits of the press/their competitors) so the gains at say 100mph will be probably be 1-2% due to the significant affect speed has on ram air gains. Assuing you start with an engine of 250bhp and assuming you've got somewhere close to Ferrari's optimised set up (which lets face it is highly unlikely) then you'll realistically see a maximum 2.5-5bhp gain at 100 mph. This is the ram air affect and not the cold air benefit............ which is worth much more but not being discussed here. Don't know what the drag effect of such a large air box is but I wouldn't be surprised if it more than matched the 'ram air' gains looking at it. Home of HTR700 Link to comment Share on other sites More sharing options...
Simos Posted April 17, 2004 Share Posted April 17, 2004 Finding myself playing devils advocate did the previous Ferrari that was the baseline of their 50bhp gain have a foam airfilter poking out of the side of the engine cover or possibly a pretty good airscoop in clean air above the drivers head which has been developed carefully over one of the longest F1 participations ever.... Just asking. Link to comment Share on other sites More sharing options...
Bob Corb Posted April 18, 2004 Share Posted April 18, 2004 Right (crack knuckles ready for big typing sesh)... I've checked what the physics is doing and come up with the following... Basically a ram air device works by translating all the dynamic energy of the airflow into static pressure. If you look at an analysis of the airflow over a car body for example there are areas which do this very well. These are the front number plate and central grilles which are vertical. (A seven windscreen is also great at this!). The buzz word is CP value or coefficient of pressure and the highest value you can get is 1 (100% conversion) but 0.99 is seen on the worst bits of a nornal car. The dynamic pressure (in Pascals) is equal to 1/2 *rho* u^2 (rho = density of air ~1.3kg/m^3, and u is speed in meters/second). Looking at the F1 car at max speed of 200mph (89m/s) the dynamic pressure is 5187 Pa (or 5.2kPa therefore if they optimise their intake and get most of that converted then the airbox pressure will be 106.8kPa (std atmos = 101.3kPa). This is a 5.6% increase in air pressure which equates to roughly 4.5% more power (if I've got my ISO1585 correction right). This all tallies up with the comments above. Now on Arnies car... I've got no reason to think that his airbox is any worse than Ferraris, I dont think the limitations on his car are so demanding as an F1 car.. So at 140mph the dynamic pressure is 2.54 kPa which is 2.5% increase in pressure which equates to about 2% increase in power or 5BHP. Those are the facts, if you get much more than that you are defying physics. The only other thing I haven't allowed for is the change in airflow direction and velocity over the previous set up. There may be some turbulent effect at the inlet runner entrance which is scuppering the tuning pulses but not so easy to analyse. At the end of the day, it looks groovy, should give a little improvement in power and has cured a flat spot. Job done Can I have one? BC Link to comment Share on other sites More sharing options...
edmandsd Posted April 18, 2004 Share Posted April 18, 2004 If you want 'ram air' get a turbo. Home of HTR700 Link to comment Share on other sites More sharing options...
Graham Perry Posted April 18, 2004 Share Posted April 18, 2004 Isn't there a major aerodynamic rule of thumb that I remember reading a year or so ago (in a book that I understood very little) that air is uncompressable below 126 mph ? Wouldn't this be a factor Link to comment Share on other sites More sharing options...
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