ZR8ED Posted May 12, 2003 Share Posted May 12, 2003 Ok So after a brief talk with John C. at the MSA show, most of the ideas talked about in my post about exhaust fumes fix and rear belly pans won't work, or are questionable at best. Cool.. no worries..Thanks very much to John for the chat. Ok.. so a rear bellpan/diffuser needs to be set very carefully or plane like characteristics can happen.. OK.. so I've heard that 7-9 degrees is best at keeping the air velocity high.. more than 9 degrees, and you can get stalling of air, and a product of slow moving air under the car is LIFT... What if you have LESS than 7-9 degrees... can you get some lift effects?... I'm not shooting for 160+mph runs or anything, I'm looking for not killing myself with fumes, or making the wrong kind of wing under the car... Its more of a wow factor (my usual reason), but also to combat fumes.. I have done pretty much everthing except redesign the exhaust.. which may happen, because the car is not "date" friendly if you get my meaning, and it is hard enough to find a good woman, without scareing her away with poisonous fumes! So.. I'm designing another bellypan, and I am mocking it from cardboard as we speak. Am I crazy?..oh yeaaaa..........Only death can stop me... Thanks for the input folks! Scott Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted May 14, 2003 Share Posted May 14, 2003 From everything I have read, being less then 7 degrees shouldnt be a problem. The difficulty will be how and where do you attach it at its forward point. Do you have a stock fuel tank? This looks like it will get in the way. I wonder if you could use a inverted gurney flap on the end of the diffuser to lower the low presure area to pull away some of the fumes. Time to get out the wool tufts and do some testing. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
johnc Posted May 14, 2003 Share Posted May 14, 2003 If you want to generate downforce from the underside of your car you need to get the air under the car moving faster then the air moving over the top. This will create a low pressure condition under the car and the entire upper surface will be pressed upon by the higher pressure air above. Ultimately what you are trying to do is create a venturi under the car. Look at the side view line drawing at the top of this page and note the shape of the belly pan: http://www.mulsannescorner.com The reason a rear diffuser typically has a 7 degree kickup is that's about as sharp a turn as the air can make and still remain attached to a simple, flat surface. You can run a shallower angle but downforce will be reduced unless you make changes in other areas. You can also run shallower angles if you're an aerodynamacist and have access to CFD software. Look at what's being done on the Bentley: http://www.mulsannescorner.com/bentleylmgtp3.htm And look at what you can do up front: http://www.mulsannescorner.com/bentleylmgtp4.html Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted May 16, 2003 Author Share Posted May 16, 2003 Thanks! I had some good pics of the car, and drew in the bellypan as I see it so far, and it looks ok on the car.. the only hard part is doing a cardboard mockup. I even found some decent mounting points on the car to attach this thing. I'm not going to run the pan under the diff. with a 280, there is a fair amount of room betweent the gas tank and the diff, so I'm going to tilt the pan up at that point, so it doesn't scoop air to the upper side of the pan. Imagine a side view... from the rearmost part of the car... 7 degree downward slope of aluminum..low enough to just clear the gas tank..the continue horizontal with the ground.. maybe 12-18"..then angle back up at like 30-50 degree angle and mount behind and above the top of the diff. Hopefully that first part won't cause lift, as I cause all the air down the centre of the car/tranny tunnel to go down under the bellypan. So far it looks ok, as the air has no where to go there anyways, and must be turbulant, and eventualy exit under the gas tank. (280Z gas tanks hang much lower than a 240 tank, and are almost as low as the diff itself.) It obstructs the view of the diff quite a bit actually. It will be mounted using solid aluminum flat bar..I won't want this thing to flap around under the car. I have allowed for 4 mounting points..it should work just fine.. I can easily see why many people don't want to try this stuff.. But Hey.. I'm running out of things to mod on the car...and its a law of dimishing returns from here on in..Increasingly more money spent for smaller gains.. Oh well.. I'm a sucker for Z punishment. Best part...Z is not stuck in garage jail... Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted May 16, 2003 Author Share Posted May 16, 2003 This is only one of several drawings I did. This one still shows up not bad once I shrunk it down to a web friendly size. This is one of my earlier drawings, and is to scale, but is not far enough back..I want it to end at the rear valence. Progess continues... Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted May 19, 2003 Author Share Posted May 19, 2003 Ok it took ALOT of cutting, fitting.. test fitting etc.. But I have a completed cardboard prototype built. It is kinda cool looking. I managed to get the horizontal part of the bellypan to line up level with the rear control arms. (mine are almost parallel to the ground) The pan is as wide as the outside pin on each control arm. Yea it seems low, but is actually higher than my diff... I can see some probs if I tried to back up to a curb...I might not be able to clear a curb with the rear... Not a huge factor, since my front air dam is only 3" off the ground...so I don't clear curbing with the front anyways.. It looks like it will be 6".. or so off the ground.. a bit less when including the 4 fences under it... All in all I'm extremely happy with it. I will now go ahead and purchase some aluminum this week, and try to recreate my prototype. After some more discussions with my mechanic, I'm now considering building another pan from the firewall to the the diff.. and have it mount between my frame rails.. A few screws, and be able to remove it for access... I am also in the fabing stages for some aluminum side skirts to blend in my rear flares towards the front of the car... They are pretty big, and I think it needs a slight ground effect (for looks) just to give it a lower look. and make it blend a bit smoother.. This one will be much easier to do... Oh yea... summer is here...I'm a sick sick man... Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted May 19, 2003 Share Posted May 19, 2003 Scott, Have you had a look at the diffusser's on the vipers and corvettes that run at lemans? I havent looked myself but i will try to find out some info tonight (lunch time now). I like the idea of the full lenght belly pan. You may as well start at your air dam and vent the under hood heat through the vents in the hood kind of like Terry O's. One thing to keep in mind is that race cars run really stiff springs and have bugger all suspension movement. One of the main reasons is to keep that belly pan area as flat to the ground as possable. You dont want under any situation for the front of the pan to be higher than the rear. Do you think you can prevent this from happening on your car? If not the whole thing is in vain. Dont forget about exhuast heat as well. I will let you know if i find anything. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted May 20, 2003 Author Share Posted May 20, 2003 ZROSSA: Thanks! I'll take all the info I can find. Yes I Have seen the LeMans cars...I think that is more or less where I found the idea. As far as bellpans go, I already have a large one that goes tight against my airdam, and goes all the way back to my oilpan. It works very well. I have had it for 3 years now, and have seen the high side of 140mph with it. It doesn't negatively affect my cooling capacity of my engine. She runs nice and cool. For the suspension travel, my frame rails are 3 inches (72mm approx) off the ground, so my suspension all ready has very little travel in it. I'll keep you all up to date on my progress.. Quote Link to comment Share on other sites More sharing options...
Guest macks Posted May 30, 2003 Share Posted May 30, 2003 Sounds great so far - if we can get something to work without having to go for a fuel cell/cut the rear floor up it'll be fantastic. Are you going to put any work into side skirts to stop air escaping out the side of the car? Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted June 2, 2003 Author Share Posted June 2, 2003 Another update. I've been extremely busy this past week, but some progess was made. The entire rear suspension was pulled out, and I raised the car 1/2 inch..maybe a tich more. I picked up another set of chevette springs for the rear, and cut them one coil less than last time, and wala.. car is raised just enough. We took it for a good test run, and the car plants itself very well in a turn, and is very easy to control. because these springs are brand new, and the other ones were used, it seems that raising the car just a bit, did not make a noticeable difference in the firmness of the ride.. ie it did not get softer.. So now that that is out of the way, the aluminum has been cut up, and is currently being bent, and shaped.... hope to have some pics of the install by the end of the week. Car runs great too!!.. I can now start turning the boost up to my desired limit.. "desired limit!?????" hehe Quote Link to comment Share on other sites More sharing options...
Drax240z Posted June 2, 2003 Share Posted June 2, 2003 Might be too late to chime in here now that metal is being cut, but free advice is free advice. 9 degrees sounds like too much to me. It is generally accepted that boundry layer seperation occurs at 10degrees or so. I would think that at 9 degrees, your car may be very sensitive aerodynamically to pitch changes. (ie: nose goes down as you lift, diffuser angle becomes more like 14 degrees, seperation occurs, back end gets light due to lack of load and downforce on rear wheels) Most diffusers aren't a flat plane, but instead a curve. Seperation tends not to happen as easily, not as drastically, and the car should be less sensative to pitch changes I believe. Anyway, just off the top of my head. Take it as you wish! Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted June 24, 2003 Author Share Posted June 24, 2003 Update. Belly pan metal brake work is going too slowly. You'd think it would be easy to find a shop with a metal brake... and when you did, one that would want to do a quicky job (coupla hrs..all labour) Hahahaha I live in a car capital in southern Ontario..there is even a speed shop in my town that ONLY touches Porsche 914's!!! no 944's or 911's for this guy.. Another only touches late model chevelles... not early models...yikes! Anyways, I found access to a metal brake... now I can make some more progress again. gees.. it took nothing to do the cutting..but when ya want nice crisp bends (couldn't do it too well with the old vice bending method we won't go there..hehe) yeeesh. Custom work is time consuming work... still driving with the windows up.... and to think i'm going to attempt to polish this thing up when its done..ahhhhhhhh Quote Link to comment Share on other sites More sharing options...
Guest Zachb55 Posted June 28, 2003 Share Posted June 28, 2003 I cant wait to see some pictures of your pan. i just cant wait to start doing things like this with my car, well actually i think imma wait till i get my 350Z to do stuff like this -Zach Quote Link to comment Share on other sites More sharing options...
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