question about aerodynamics on my 323

[racerboy146]

I know this is a forum for ecomodding, and a race car is the exact opposite of ecomodding, but I have a race car and I don't know as much about aerodynamics as I'd like to know, and I was hoping maybe you guys could help me out. (Although, with the amount of aerodynamic stuff I have planned for this car, maybe it might get better fuel efficiency, therefor maybe it is ecomodding after all. ) Also, sorry for the long post, but I want to give as much info as possible, so that you guys can picture the car, and help me.

Anyways, here is a little background info on the car. I have a 1992 mazda 323 hatchback I am going to be building into a race car, and I am planning on doing tons of aero mods on it to reduce drag and increase downforce over the front tires to help turn the car better. (First I gotta fix all the dents, though. lol) I plan on chopping the roof down a couple inches for drag reduction, but it's going to be a lot of work. I'd like to make it as simple as possible, so that it doesn't take as long to do, and I have been thinking about leaving the rear hatch off the car when I'm done for multiple reasons, including: the time it takes to modify the hatch to fit the chopped roof, less weight (reducing weight is VERY important to me), and our not running a rear hatch window. I can't run a window on the driver side door, due to safety reasons (doors are welded shut, and I need a way to get out quickly and safely in case something happens like a fire, or something), and I'm guessing that will let air into the driver compartment. I'm guessing with a rear hatch window, the air in the cockpit would have nowhere to go, therefor causing a parachute effect. I am planning on sealing off the rear side windows (and maybe the passenger side window) with lexan for aerodynamic reasons. And this leads to my question. Should I remove the rear deck lid? Without the glass, I'm guessing the aerodynamics are already not that good, but will removing the rest of the hatch make the aerodynamics worse, or better? Without the hatch, I am guessing that whatever air is in the driver compartment will escape easier, but I'm new to aerodynamics, and don't know if my thoughts are correct or not. I am attaching a picture of the rear hatch area so that you guys can maybe help me figure this out.

Thanks

[chrisgerman1983]

I cant be much help but I have often wondered if removing a hatch would help drag? it seems like it could help because the suction would have nothing to "grab" I really don't know though If I had to run windowless I would build a coroplast pan for the interior with just an opening for you. The kind you would see on a convertible race car. then remove the back window to let air out?

[racerboy146]

I would love to try that, but I don't think the tech guys would like that. The class I'm racing in is suppossed to be 100% stock, but they don't really enforce the rules. (They have been allowing most guys to get through headers, cold air intakes, racing cams, and other stuff through.) But I don't want to be too obvious and push it too far. And I think putting a coroplast pan in the car would cause the car to stick out like a sore thumb. Good idea, though! I never would have thought of it. If you guys have any other ideas to make the car more aerodynamic, yet not stick out, let me know. I plan on running a front air dam, side skirts, headlight/grille opening covers (we aren't allowed to run any stock plastic stuff, so there would be no headlights or grille), a wiper cowl cover (to smooth out the air flow), and I plan on covering the door handle holes. Also, I forgot to say, this is a circle track class. If that makes any difference.

[aerohead]

The airflow direction is a function of static pressure,from area to area.
The lowest pressure on your car is near the A-pillars where the air is accelerating violently around those corners.
If you remove the rear hatch,the air will actually flow from the open rear,forward through the car to the open front windows,bringing exhaust fumes with it.
Since the carbon monoxide won't be improving your driving abilities,it's best to keep the hatch,but do the Lexan if it will reduce mass.

[racerboy146]

Hmm. Never thought of the exhaust aspect. Although, I don't know if that will really affect me, as the exhaust will be exiting under the car, instead of behind it. (I was planning on having the exhaust exit a foot or two in front of the fuel tank, with a turn down.)

[aerohead]

Originally Posted by racerboy146

Hmm. Never thought of the exhaust aspect. Although, I don't know if that will really affect me, as the exhaust will be exiting under the car, instead of behind it. (I was planning on having the exhaust exit a foot or two behind the fuel tank, with a turn down.)

There's still an opportunity that the air mass containing the exhaust will be swept up into the wake,which would then have a chance to visit your lungs.

[freebeard]

I'm going to guess 24 Hours of LeMons.

If you're required to have the window open, maybe a 'West Coast' mirror the height of window that's half in and half out to redirect the air?

[racerboy146]

Originally Posted by aerohead

There's still an opportunity that the air mass containing the exhaust will be swept up into the wake,which would then have a chance to visit your lungs.

hmm.... I think I'll just have to live with it. Besides, now that I think about it, won't not having a rear hatch window let the exhaust gasses in? Nobody runs hatch windows in our series. (Then again, most don't run any windows at all except for the windshield, so maybe all the exhaust gets mixed with air, and therefor isn't really harmful.

Originally Posted by freebeard

I'm going to guess 24 Hours of LeMons.

If you're required to have the window open, maybe a 'West Coast' mirror the height of window that's half in and half out to redirect the air?

I wish it was a 24 hours of lemons. But sadly, I don't have the money it takes to race in that series. I race in an enduro series that travels all over wisconsin, and runs 150 to 300 lap long races on both dirt and asphalt oval tracks. Entry fee is only $25, unlike the $500+ of the lemons series. As for the west coast style mirror to direct airflow away, I might do that, or I might make some air deflectors out of lexan.

[freebeard]

Those plexiglass dog-leg things you see on minitrucks might work; but I like the idea of daring the inspectors to disrespect your rear-view mirror.

I suppose a full boat-tail is out, but you might check the regulations. Wheel spats that would work on a dirt track is an interesting engineering problem.

What should I put in Google Image Search to see what runs in that class?

[racerboy146]

Well, I'll have to think about the mirror. And what do you mean by plexiglass dog leg things? Do you have a picture of what you mean?

Yes, full boat tail is out. lol. That would be pushing the rules way too far. And I don't want to do wheel spats. Reason being I need to be able to quickly change tires during a race, and putting wheel spats on would make it much harder to do a quick tire change. Not to mention, we do bump and rub other cars a bit, and I don't want to cover my wheels, as the covers could get pushed into the tires, and pop them. Also, I need the brakes to get as much air as possible, and covering the wheels up would eliminate much of the needed air.

Also, here is a link to a photo gallery of one of our races. Ignore the full sized cars in some of the pictures. This was a special event that had two series racing each other, and the other series runs v8 cars as well as 4 cyl cars, while we only run 4 cyl cars. And yes, the cars are all beat up and not aerodynamic. But that's where I'm hoping I can get an advantage. http://mdmracepix.autoracingtracks.c...29-11/page/25/