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Old 01-23-2013, 03:03 PM   #61
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Ambient temp is really not a significant issue - your exhaust gasses are 1500 degrees either way, so whether it's 40* outside or 100*, if the heat in the transmission tunnel for example is going to overheat components, it will probably still happen.
You're worried about the exhaust pipe itself heating things? Yes, the exhaust gasses are pretty warm, but much of the engine bay is in the ~200-300 degree range, where 50 degrees will make a substantial difference. I certainly wouldn't wholly discount the ambient temps.

Good call on the diff cooling though.

I like the shapes of the ports in the undertray on the porsche...
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Old 01-23-2013, 06:03 PM   #62
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With the underbody we want the air under the car to move faster than the air around the car. I don't know how a much of NACA ducts disturb the air under the car (would need help, but i know plucas is busy) If any one has details on how much air is disturbed because of it. Or run a NACA duct right before the diff, then right after redeposit the air right after the diff. Or also will pulling the air from under the car up to the trani tunnel cause more downforce?
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Old 01-23-2013, 06:14 PM   #63
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the whole point of NACA ducts is that they don't disturb airflow.

NASA are smart.
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Old 01-23-2013, 06:45 PM   #64
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the whole point of NACA ducts is that they don't disturb airflow.

NASA are smart.
Yes. A naca duct feeding air to the diff shouldn't disturb the rest of the airflow on the underbody.

Feeding the air back to the outside world is an important point, too. The duct to return airflow after the diff should allow the air to accelerate as it rejoins the underbody airflow for minimal disturbance and maximal airflow over the diff.

At least this is what the book tells me.
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Old 01-23-2013, 07:44 PM   #65
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I like all the underbody stuff - er, for fuel economy (though I wouldn't mind better accel at low triple digits just for spirited street driving).... It doesn't show, less likely to get you nightsticked and your car taken away. I'd love to do a spoiler for the same reason, but somehow can't imagine that not labeling me as "ricer".

Really like the early post with the rails welded to the stock frame.
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Old 01-24-2013, 03:58 AM   #66
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Originally Posted by AbeFM View Post
You're worried about the exhaust pipe itself heating things? Yes, the exhaust gasses are pretty warm, but much of the engine bay is in the ~200-300 degree range, where 50 degrees will make a substantial difference. I certainly wouldn't wholly discount the ambient temps.

Good call on the diff cooling though.

I like the shapes of the ports in the undertray on the porsche...
My first flat underbody prototype that I ran at Auto Club Speedway deformed from exhaust heat, so depending on the material used, that heat can be a big factor. As far as components go, both the trans and diff will run substantially hotter in a sealed tunnel that is being superheated by the exhaust compared to having an open underbody with ambient air flowing along everything. The oils in both of those units don't like heat much. Those are the two biggest problem areas in my eyes.

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I don't know how a much of NACA ducts disturb the air under the car

A properly designed and constructed NACA duct creates almost zero disturbance to the airflow, that's why they are so bad-***.

-Ryan

Last edited by ThePass; 01-24-2013 at 04:15 AM.
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Old 01-24-2013, 08:12 PM   #67
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It *seems* to me that getting a few vents would fix up your problems... The issue is all the air feeding the tunnel in a sealed box is passing through the radiator. That's not a lot of area (so not a lot of velocity) and it's heated air.

Putting in a few ducts would probably help a ton. As would coolers.

But for pansies like me who just want good gas mileage with the occasional mountain switchback or stoplight race, I don't think I get that much heat in there.....
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Old 01-24-2013, 09:18 PM   #68
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Default flat bottom pictures

We're planning a flat bottom for the Catfish. The floor is flat until the rear diffuser, which should make some free downforce out back. The Thunderhill car had neither flat bottom or the diffuser--time constraints.

Brian Goodwin's race car is also shown from the back. He's got a full flat bottom on his car and he says he notices the downforce going over the start/finish rise at Laguna Seca. Our extends beyond the rear bumper, and has a gap between the bumper and the diffuser to prevent the rear fenders from catching air.

Canards molds are also being made. I'll be making some that fit stock Miatas as well.

Miata Flat Underbody-difus-dim.jpg

Miata Flat Underbody-17031216.jpg

Miata Flat Underbody-back_perspective.jpg

Miata Flat Underbody-diffuser-wings.jpg

Miata Flat Underbody-img_4023.jpg

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Old 01-24-2013, 10:16 PM   #69
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AbeFM - Between man hours and materials, I think it would take a long time for the additional gas mileage efficiency to pay off the cost of making a whole flat underbody... Not worth it IMO. Trying to get 5 more mph at the end of the front straight at a track? Worth it IMO.

cordycord - That looks like Tony's (AWR) shop. Is it?

-Ryan
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Old 01-24-2013, 10:34 PM   #70
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Originally Posted by cordycord View Post
We're planning a flat bottom for the Catfish. The floor is flat until the rear diffuser, which should make some free downforce out back. The Thunderhill car had neither flat bottom or the diffuser--time constraints.

Brian Goodwin's race car is also shown from the back. He's got a full flat bottom on his car and he says he notices the downforce going over the start/finish rise at Laguna Seca. Our extends beyond the rear bumper, and has a gap between the bumper and the diffuser to prevent the rear fenders from catching air.

Canards molds are also being made. I'll be making some that fit stock Miatas as well.

Attachment 65501

Attachment 65502

Attachment 65503

Attachment 65505

Attachment 65506

Attachment 65507
How do you keep the flow attached on the diffuser with a 39 degree angle?
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Old 01-24-2013, 11:44 PM   #71
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Quote:
Originally Posted by plucas View Post
How do you keep the flow attached on the diffuser with a 39 degree angle?
+1

And that diffuser on the yellow car goes against the little I know about what works in aerodynamics. I've never seen a diffuser that is shaped like an S.
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Old 01-24-2013, 11:55 PM   #72
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+1

And that diffuser on the yellow car goes against the little I know about what works in aerodynamics. I've never seen a diffuser that is shaped like an S.
The highest with out a wing or spoiler is 14 deg before separation. Now if you have a vary powerful wing or spoiler I could see it working more efficient.
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Old 01-25-2013, 12:12 AM   #73
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Well, a very gradual curve could probably maintain attached flow even if it ultimately reached an angle steeper than the generally accepted max of ~15*, but that's not gradual, it's pretty sudden. From what I understand too, that doesn't look like a great design.
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Old 01-25-2013, 12:35 AM   #74
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+1

And that diffuser on the yellow car goes against the little I know about what works in aerodynamics. I've never seen a diffuser that is shaped like an S.
Same. In for education if I am wrong but that diffuser looks stalled to me.
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Old 01-25-2013, 01:25 AM   #75
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iv been inspired by this thread. im gonna start mine this weekend. just the center section for now to match up with my flat front belly pan
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Old 01-25-2013, 02:34 PM   #76
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Same. In for education if I am wrong but that diffuser looks stalled to me.
Brian Goodwin swears by it (yellow car) and says he's had to re-program his brain post-flat bottom and diffuser, as the new cornering speeds he's using would spin him off the track pre-ground effects.

I'll tell you just how good/bad our diffuser works, once we get it on the track.

My diffuser s hinged and adjustable up and down, so you can consider the angle a "street configuration", which was the plan from the start. The angle is lowered via threaded rods. I'm as anxious as anyone else to test this aero.

The front splitter in the picture mates exactly with the outline of the body. I've made a larger version for track use, and i'll be trying front canards as well.

Can't wait to get it on the track.
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Old 01-25-2013, 02:39 PM   #77
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Originally Posted by ThePass View Post
AbeFM - Between man hours and materials, I think it would take a long time for the additional gas mileage efficiency to pay off the cost of making a whole flat underbody... Not worth it IMO. Trying to get 5 more mph at the end of the front straight at a track? Worth it IMO.

cordycord - That looks like Tony's (AWR) shop. Is it?

-Ryan
That's Tony's shop, AWR. Brian's (Good-Win Racing) flat bottom was done there, including rear diffuser, and we developed ours with some of the input from that build.
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Old 01-25-2013, 02:49 PM   #78
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That's Tony's shop, AWR. Brian's (Good-Win Racing) flat bottom was done there, including rear diffuser, and we developed ours with some of the input from that build.
Cool. I have to ask, is the Catfish something that Tony helped build/design with you guys? Because about a year ago he had a basically tube-frame chassis sitting around with miata seats/engine/trans/wheels/etc. and he was talking about how it was going to be a super lightweight version of the miata once it ever got finished, and when I saw the Catfish come out, it looked like a pretty similar chassis under the skin.

-Ryan
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Old 01-25-2013, 03:15 PM   #79
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Originally Posted by ThePass View Post
Cool. I have to ask, is the Catfish something that Tony helped build/design with you guys? Because about a year ago he had a basically tube-frame chassis sitting around with miata seats/engine/trans/wheels/etc. and he was talking about how it was going to be a super lightweight version of the miata once it ever got finished, and when I saw the Catfish come out, it looked like a pretty similar chassis under the skin.

-Ryan
I was working on another car of mine at Tony's and watched a steady stream of Miata race cars roll through the shop. The simplicity of the Miata--while I was trying to fix one problem after another with mine--was the impetus to use it as the Catfish donor. The first donor was sourced through Tony ($800), and Tony helped set up the first frame for the El Toro testing you see on Youtube. Tony is a great source of knowledge for chassis and suspension setup.
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Old 01-25-2013, 03:17 PM   #80
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AbeFM - Between man hours and materials, I think it would take a long time for the additional gas mileage efficiency to pay off the cost of making a whole flat underbody... Not worth it IMO. Trying to get 5 more mph at the end of the front straight at a track? Worth it IMO.

cordycord - That looks like Tony's (AWR) shop. Is it?

-Ryan
Heh. Goofy priorities. :-P

I'm not sure how much I would do - likely not all the diffuser bits, as they'd show from the outside anyway... And I need to do SOME radiator shrouding again. But a certain amount of very thin metal or metal/plastic could work out to have tangible benefits without quite as much work as it seems?
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