260DET Posted March 18, 2010 Share Posted March 18, 2010 Having got my lent copy of Competition Car Aerodynamics back, finally, there is a mention of using a diffuser design in the front undertray, will have to study that more to see if its a practical design for the Z. Quote Link to comment Share on other sites More sharing options...
260DET Posted March 21, 2010 Share Posted March 21, 2010 No interest? To complete the subject for anyone searching later, I'm going to look at a double diffuser design venting into the wheel well areas. The single central design has a venting problem due to it being in front of the engine, there is no low pressure area there like there is in a wheel well. The pic below illustrates what I have in mind but note I don't want to vent in front of the wheels, just between them and the engine. There are high pressure areas in front of wheels, I'll be looking at some sort of curved air deflector in front of them. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 21, 2010 Author Share Posted March 21, 2010 (edited) No interest? To complete the subject for anyone searching later, I'm going to look at a double diffuser design venting into the wheel well areas. The single central design has a venting problem due to it being in front of the engine, there is no low pressure area there like there is in a wheel well. Unless you have a flat undertray and a diffuser in the back of the car. It is interesting and I was just using that same CFD image to prove a point elswhere about a week ago, fig 4-14 if memory serves. The pic below illustrates what I have in mind but note I don't want to vent in front of the wheels, just between them and the engine. There are high pressure areas in front of wheels, I'll be looking at some sort of curved air deflector in front of them. The diffuser would be illegal for most SCCA classes, but certainly worth doing if you don't have those constraints. The high pressure in front of the wheels isn't so bad on a sedan, and really isn't bad on a lowered race car. On an open wheel car I seem to remember they're responsible for a majority of the drag. If you just get the air directed at the wells the low pressure will do the rest. Unless you have your diffuser quite a bit lower than the frame rails, I don't think you'll have too much room to raise it up where it won't be in front of the wheel. Edited March 21, 2010 by JMortensen Quote Link to comment Share on other sites More sharing options...
260DET Posted March 21, 2010 Share Posted March 21, 2010 If the wheels are in front of the diffuser exit I was thinking that when turning they would interfere with the air flow a lot. A deflector should help isolate any variation in air flow from that, as well as do something to reduce wheel induced drag. The thing I like about having a diffuser instead of a venturi is that it should work fairly constantly during variations in ride height and roll. A venturi on the other hand relies on the presence of the ground to form its shape so any variations there would vary its effect quite significantly. My Z presently has a front venturi setup, some times for no obvious reason the car will understeer at high speed in corners, other times it is rock solid. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 21, 2010 Author Share Posted March 21, 2010 My Z presently has a front venturi setup, some times for no obvious reason the car will understeer at high speed in corners, other times it is rock solid. Exactly why I started the thread in the first place. Quote Link to comment Share on other sites More sharing options...
260DET Posted March 22, 2010 Share Posted March 22, 2010 Yes, and it looks like we have an answer in a round about way Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 22, 2010 Author Share Posted March 22, 2010 So you're also thinking lower your car and up the spring rate? I don't think the diffuser is going to help the problem you're having. I'll be happy if you prove me wrong though... Quote Link to comment Share on other sites More sharing options...
260DET Posted March 22, 2010 Share Posted March 22, 2010 My philosopy is to get the mechanical grip right then, and only then, add aero. Seeing the diffuser concept is in theory less potentially problematical than a venturi I will go that way. If the car still tends towards high speed understeer then it probably is the driver, it usually is Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted April 3, 2010 Share Posted April 3, 2010 We took the splitter off the twin turbo ford GT and immediately picked up 20mph and eventually went 252.9 in the standing mile. Of course....this car has completely different front end, undertray, and upper body dimensions. Quote Link to comment Share on other sites More sharing options...
260DET Posted April 4, 2010 Share Posted April 4, 2010 20 mph is an awful lot to pick up, sounds like the splitter design was not the best so it just goes to show you that OE is not always best. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 18, 2010 Author Share Posted October 18, 2010 (edited) Emailed McBeath about my splitter/airdam combo idea. Here is the response I got: If you think can't smooth out the underside and integrate a diffuser then probably the lower the airdam is at the front the better. Combining this with your idea of (effectively) extending the lower part of the airdam forwards would offer a horizontal surface onto which the stagnation pressure in front of the car's nose could act' date=' which would probably add a bit more downforce than you'd get from a straight vertical airdam in line with the front. And yes you migth extend the area on which the low pressure beneath would act. However, if you could panel at least under the engine bay so that you could benefit from a splitter as the lowest part of the airdam/splitter assembly I think in reality there'd be the potential for more downforce. I know this isn't what figure 4-11 suggests when viewing the relative magnitudes of the low pressure regions, but the model was relatively simplistic here and I don't think it necessarily reflected what would happen in the real world. A splitter would ordinarily feed into a flat panel downstream, and even into mini diffusers between the wheels and the engine, and this would extend the darker blue region you see directly under the splitter in the lower inage in fig 4-11. The sensitivity of a splitter increases the nearer to the ground it is obviously, and if the splitter height is on the same plane as an under-car panel, I'm guessing it wouldn't be so low as to cause you problems in this respect.[/quote'] So he thinks my idea has some merit, but the splitter/diffuser to flat bottom to diffuser underside is a better idea for ultimate downforce production. My main beef with the undertray idea is that it seems really hard to do. His comment also seems to indicate that the splitter height can be fairly high off the ground and still function, which makes me wonder what went wrong with John's attempt. Edited October 18, 2010 by JMortensen Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 30, 2010 Author Share Posted October 30, 2010 (edited) Looks like the car that was fastest in the UTCC has my splitter on it. It's that crazy fast Hemi Challenger: http://grassrootsmot...m/utcc/updates/ Edited October 30, 2010 by JMortensen Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 31, 2010 Author Share Posted October 31, 2010 (edited) Emailed Mr. Bunch and got a long response. Here is the meat with regards to the airdam/spoiler combo: . I had that piece of conveyor belt on the leading edge, but no more because I am convinced that it messed up my air flow under the car. That skirt might help function as a damn, but will screw up the air flow under the splitter. It was the first time I had ever done that too. Also my splitter was too flat, on hard acceleration it was up in the front. A good material for a splitter is black nylon etc that Plastic suppliers stock. It can take lots of rubbing and wears great. That is what I am changing to now. 1/2 inch thick. So it looks like he thinks it's better without. Edited October 31, 2010 by JMortensen Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 31, 2010 Author Share Posted October 31, 2010 Been emailing some more with Glenn, and I think what would help is a look at the rear of his car. It has a HUGE diffuser on it and apparently a full undertray as well. He was a bit confused about what I was asking, but we finally worked it out. He ended up saying: "Dont put the [airdam] on the splitter, unless you are only interested in an air dam and are willing to forget about the downforce of that tray and the splitter." This makes perfect sense. You need air to the diffuser, so if you're running a diffuser, then an airdam isn't helping. Still leaves me wondering what to do since I can't run an undertray for autox but have no rules to follow for track days... He also said that they changed so much stuff on the car that the driver was having a hard time getting the most out of it. He thought they had another 3 seconds per lap in there but they broke in the first session after only 3 laps and still won outright. Impressive. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted October 16, 2011 Share Posted October 16, 2011 (edited) FYI - I added a splitter. Made of 1/4" plywood as a test piece. Extends 2.5-3" in front of the airdam and back to the front swaybar. Dropped 1/2 second lap time with no ill effects. It was noticeable from the drivers seat in med+ speed sweepers and seemed to help braking as well. The cheapest 1/2 sec you'll ever find and it doubled well to mow the grass. Lets just say the splitter planted to front end so well that I could apply significantly more throttle in some turns. Pushing it too hard I power on oversteered ... cracked a rear stub axle flange. Now need to find a permanent material although it's got a nice natural green patina. Cameron Edited October 16, 2011 by heavy85 Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 16, 2011 Author Share Posted October 16, 2011 Did you try the airdam on it? Quote Link to comment Share on other sites More sharing options...
heavy85 Posted October 17, 2011 Share Posted October 17, 2011 Did you try the airdam on it? Nope. Only run two races with it and was astounded by my lap times in each so haven't touched it. Not really planning anything else for next year other than to make it out of stiff plastic or something that wont warp when it gets wet. Cameron Quote Link to comment Share on other sites More sharing options...
texis30O Posted October 21, 2011 Share Posted October 21, 2011 I am currently working to put a splitter on my car. I have sourced a plastics manufacturer locally I spoke with a miata performance company out of Dallas that made splitters. He gave me a list of parts they used as well as design ideas. I should have something in a few weeks. Money is really tight for me right now, pregnant wife, toddler, and training for a adventure race........ So my time is limited on the z... I will post up pice when I have it done. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted May 24, 2013 Share Posted May 24, 2013 Keep it coming guys... giving me more ideas for how to address the splitter on mine... Quote Link to comment Share on other sites More sharing options...
LanceVance Posted May 24, 2013 Share Posted May 24, 2013 (edited) I picked up a used Tegris NASCAR splitter for under $50 shipped. It will require some trimming to make it work on the narrower Z, but it should work great when done. I'm planning on using some rubber impregnated cloth connected along the trailing edge to make an under tray of sorts. My main concerns were cost and ease of replacement, not weight like yours however. Edited May 24, 2013 by LanceVance Quote Link to comment Share on other sites More sharing options...
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