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Old 01-06-2008, 09:52 PM   #21 (permalink)
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Quote:
Originally Posted by Coyote X View Post
The question is how high should the car be off the ground with a flat underside?
I have read: between 1.5 to 3 inches, with 3 being quoted more often (besides 1.5 isn't quite practical for a road car, is it?). But I can't find the $*&$ sources at the moment.

Knowing the underside of the car, your largest source of underbody drag (with a smooth belly in place) is going to be the control arms. So if you can lower the suspension enough to get the belly pan at least level with, or slightly below the bottoms of the control arms, I'd say that's where you've probably achieved the most drag reduction.

How high would that have you off the ground, and what would it do to your suspension geometry?

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Old 01-06-2008, 09:54 PM   #22 (permalink)
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Also - if possible, try to taper the belly pan upwards after the rear suspension, at no more than about a 10 degree angle.
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Old 01-06-2008, 10:24 PM   #23 (permalink)
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I was thinking of making it totally flat from the bumper lip in the front to the bumper lip in the rear. If I did that I could lower it maybe 1/2 inch lower than stock to make the control arms sit level with the pan. I would like it lower so if you think that going lower than that won't affect anything I will probably just use my chopped XFi springs.

I could angle the rear upwards some and just cut that rounded lower section off the bumper and just make it like a smooth roll pan on the back.



From that pic you can see the rounded part of the bottom of the bumper, if I cut that off that would give me a slight upwards angle on the rear of it.
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Old 01-06-2008, 10:35 PM   #24 (permalink)
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Know what else would be cool - stretch some rubber over the rear control arms, so you can still have full travel, but a clean aero membrane when riding flat & level. I was thinking the same membrane connecting the pan ahead & behind the front control arms would be good... and then rememebered the wheels have to steer too.
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Old 01-06-2008, 10:47 PM   #25 (permalink)
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If I drop it to the bump stops I can just go over the control arms with the cover since they will be up higher

I could cut away part of the pan where the wheels turn and leave the rest alone. That would get most of the control arm covered.

On the rear I could build basically a sealed system that gave the tread 1/8" clearance and the back side could be near form fitting and let the wheel shape it precisely for me. That could join with the wheel skirts to keep all air out of the rear wheel well.

I will get it on it's side again this week and get some pictures and try and illustrate what I have planned so you can see it better. School starts back tomorrow so I will be busy with registration and junk this week probably unless I can get out of it again
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Old 01-07-2008, 12:54 AM   #26 (permalink)
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Turtle too low can be bad.

Quote:
Originally Posted by Coyote X View Post
The question is how high should the car be off the ground with a flat underside?

I would believe your minimum under body ground clearance should be 5.5" . When i worked for the corner gas stations, I saw more than one slammed ricer get stuck on our speed bumps. Damn that was funny.
Here in the great Commonwealth of Va. dot regs say they (speed bumps) are not to exceed four(4) inches in height. Real world speed bumps can be as tall as six inches.
However with a light enough car you just pick up the backend and push it the rest of the way over.
Happy motoring. S.
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Old 01-07-2008, 01:37 AM   #27 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
I was thinking the same membrane connecting the pan ahead & behind the front control arms would be good... and then rememebered the wheels have to steer too.
Why not have a piece that's attached to the upright, and turns with the wheel?

Quote:
Originally Posted by metroschultz View Post
Here in the great Commonwealth of Va. dot regs say they (speed bumps) are not to exceed four(4) inches in height. Real world speed bumps can be as tall as six inches.
Than why not go for 5", and if you find anything over 4" make them shave them down to the VDOT specs?

Another thing to consider is your approach angle. So, with 5" ride height, and fully compressed suspension what's the maximum angle you can approach; "the steep driveway conundrum."

As for ducting. Just think "P-51". I'd have to find/unpack some books to try and estimate opening size . But <generalizations>you'll get lower drag with a duct from the opening to the radiator and from the radiator to the exit. The exit should be "variable", so that changing the exit size will increase the low pressure zone at the exit and promote flow at lower speed (the fan does the same thing). But you'd want it in a location of low pressure to begin with. Water cooled engines still benefit from air cooling, but you could probably figure that out after getting it running again, and just pop some variable vents in the hood (in it's low pressure zone) that can be tweaked open based on OAT, ECU closed/open loop, under-hood temp and mph (or just use your brain and a lever).</generalizations>
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Old 01-07-2008, 12:11 PM   #28 (permalink)
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Good question on the ground clearance. I was going to build it with 5", and so have about 4" loaded? My car will have no overhang front or back and that helps a little on the clearance issue. To build my frame I was going to do the floor panel flat on the garage floor. The sides would be roughed out on the garage floor separately, and then just stand them upright on the floor panel and welded on? Then add the roof? Yes this light a frame shouldn't be that hard to move around.
Good luck!
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Old 01-07-2008, 12:16 PM   #29 (permalink)
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I like it so far I used to have a Geo Metro back in the day. Everyone used to make fun of me for it lol.
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Old 01-07-2008, 09:41 PM   #30 (permalink)
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Didn't do much today to the car other than cut some holes in it with a plasma cutter

I did stick a fence post inside the rocker to see if the tube would actually work.


The plan I have for the chassis seems like it will work good. I can just mount the main tube on the passenger side the way the car is sitting now then lay it on the other side and do the same thing to the drivers side. Once those bars are in place and locating the inner control arm mounting points. I can start cutting away the rest of the structure and building the chassis one part at a time. I still think once I get those main tubes installed I should lay a sheet of metal on the floor and weld the jackstands to it and also to the control arms so the car can't shift or move in any way as I cut the unibody away.

The rear will be easy.

I can leave that center piece alone and notch it to run a tube through and weld it onto the tube. Then the spare tire area can be cut away from it. Once that is done the rear is basically done, I just need a shock tower and spring perch. Then a U shaped pipe to replace the rear bumper. None of that will have to be really much precision though so that makes it much easier.

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