Z aerodynamics...why so bad?

[innerware]

I am sure this has been covered but I couldn't find it. Why are the Z's aerodynamics so bad as to let in exhaust when a seal is bad? What can be done to change the air flow around the car to stop this? Do any of the aero packages from MSA change the air flow enough? Any spoilers or such? I think that I have all my rubber replaced at the rear of the car but I still get the fumes. It seems to be coming in from the windows (when open) I still have a lot to look at though but I thought I would ask.

 

Thanks in advance,

Kyle

[CruxGNZ]

Here, if you're curious, you can read up on the early Z's aerodynamics here:

http://zccw.org/Tech/Body/09-97EarlyZAerodynamics.html

 

For exaust fumes inside, make sure you check out and replace if needed ALL seals in the rear (tail light, hatch), floor, doors and fire wall.

 

I remember this post had some good information in it about exaust fumes.

Click Here

 

!M!

[Guest bastaad525]

I've asked about this so many times... Not so much the aerodynamins in general, but about what you could do to affect them and keep the exhaust smell from getting in the car. Some people have claimed that adding a rear wing/spoiler can help with the fumes... where some people say they do not, and a couple guys actually said the wing made them worse!!! I never got around to asking which results were from using which wing, so that might make a difference. Of course the real solution is just to make sure ALL your seals in the back of the car are in good shape, and to go thru and find all the openings back there and seal them up. There are holes around the fuel tank filler, in the spare tire well, under the radio antenna, next to the rear shock towers, and in the rear hatch itself that can all let fumes into the car. Some came with a seal, some never had one to begin with. Unfortunately, I think you can never really get 100% rid of the smell, at least not when you're driving with the windows open. I've already gone thru the back like 10 times eliminating every opening I could find. The next thing on my list of ways to get rid of it is to install a catalytic converter, and this is the thing I think will get rid of it once and for all. I think it will be worth whatever small sacrifice in performance this will cause. Personally, after thinking on it a lot and getting a general consensus from lots of guys here, I do not think adding a wing or other aero parts will get rid of the problem.

[Z-TARD]

I don't think any areo kit would help either, seems to me that the fumes entering the car come in from inside the rear cargo area, where there are unsealed holes and seems almost beyond count. Fumes can't really come into the open windows at any forward speed, unless you have a really stout tailwind maybe. I think what is happening is that the open window allows air pressure to escape from inside the vehicle, allowing the high pressure air trapped under the rear valence to vent upwards into the interior through all the unsealed holes back there. There is also the vent can for the fuel tank ack there as well on the passenger side cargo area, behind the plastic trim. Sometimes these rust out and let gas fumes into the car. As far as the areodynamics goes, The Z's large grill opening and open headlight buckets are what really kills it. From the outside, the exterior looks very sleek and areodynamic, but what the air sees as it meets the car at high speed is mostly firewall and headlight. Cut the entire nose section off of a Z from the cowl area forward, and it is a pretty good representation of the true areodynamic shape of our cars. Probably the biggest improvements you can make would be to minimize the size of the opening in the grill, and install headlight covers. A step further than that would be to provide a vent in the hood for all the air that does enter the engine bay through the grill, check out BlueovalZ's car for a good example of this:http://www.fototime.com/ftweb/bin/ft.dll/pictures?userid={7DC317B0-8EDB-4B2E-A837-F708D07C9769}&inv=9C67398D46D99D9&userid={7DC317B0-8EDB-4B2E-A837-F708D07C9769}&inv=9C67398D46D99D9

 

Making a belly pan under the engine compartment would also help things out a lot. It would prevent all the air that enters the grill from being ejected out the underside of the car, this is mostly what is responsible for our cars being so unstable at high speed in stock form, as the nose tends to try rotating for take off above about 90 MPH. Hope this helps a little,

 

Mike

[innerware]

Thanks guys. All the posts helped a lot and again I am thankful for all the great knowledge you all possess. Blue oval's car kicks butt too. As for the article on aerodynamics it has made me look at all cars differently now. Really is amazing how much crap there is not flush on a Z. My wifes Corrolla is more aerodynamic than my Z. Doesn't look as good mind you but way smoother. Has anyone made a belly pan for there car yet? If so what does it look like? The gaurd under the radiator, is it bad that that is removed?

 

Anyway thanks again,

Kyle

[Mikelly]

Kyle, that is the real issue... Overcoming the dreaded CGs of the early Z. DOn't waid into those waters haphazardly. Make sure you test every aerodynamic change you make in small incriments. Zcars have been known to do some very funny things at speed with the wrong aerodynamics.

 

In 1999 I did several passes with the aid of a State Trooper friend. My car was a 74 260Z. It was powered by a 383 Stroker Chevy with a 6 speed. Car had a 3:73 lsd in it, MSA front airdam with brake ducts, a Jim Cook Racing whale tail, MSA lowering springs, and Koni Red "D" series struts. It was flared in the rear and was running 265-50-15s out back, with 225-50-15s up front. I also had a flat bottom aluminum fuel cell and some WIDE and FLAT frame rails that I welded in. Those rails hung down 2 inches below the floor pans. I made passes in the 145-150mph Range with LITTLE effort. I pushed the car into the 160s and CRACKED the rear whale tail at the seam along the hatch. However, the car was very stable.

 

I suspect that if the rear tail had come off the car, I'd have had my hands full. However, it does give some indicator about how much downforce those whaletails generate!

Mike