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Top-down Aero Mods

 
Old 06-21-2019, 04:12 PM
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Default Top-down Aero Mods

Having perused the aero section, it seems unanimous that the best aero is with a hardtop, followed by softtop up, with the worst being soft top down. However, it is also agreed that top down/off is more fun, with a more intimate road feeling.

So, top down for enjoyment. AutoX, canyon carving, etc.
For a street car that you intend to put on a track, but the primary function is fun, what up top aero can you do?
Will vortex generators work at the top of the windshield?
Will a wing do anything with all the 'messy' air up top?
Is there anything you can do to the rollbar that will help 'clean' the air up top?

My budget is embarassingly low, so plywood and scrap materials that can be repossessed are my main options.
Thanks
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Old 06-21-2019, 04:51 PM
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Splitter and high mounted rear wing will still work fine.
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Old 06-21-2019, 10:52 PM
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Any idea how high it'd have to be? Ideally, I'd like to not block the rear view mirror, but I haven't installed it yet so... it wouldn't be the end of the world...
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Old 06-22-2019, 07:55 AM
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Nine lives racing and swan neck, or most straight mounts for it are out of the line of sight
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Old 06-22-2019, 09:54 PM
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Areo? Who cares. Do what you like.

The only people who run top down are autoxers and they use 10" spoilers attached to the trunk lid. I can tell you even on a track the drag keeps the back end from being frisky.

The other top down areo solution is to cut off your windshield.
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Old 06-24-2019, 09:24 AM
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Originally Posted by Canyonfive View Post
The only people who run top down are autoxers and they use 10" spoilers attached to the trunk lid. I can tell you even on a track the drag keeps the back end from being frisky.
That's because that is what the rules limit many classes too. If they could use wings, they would.
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Old 06-24-2019, 02:35 PM
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What are you trying to accomplish? If you're trying to have fun, track top down and forget the aero.
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Old 06-24-2019, 03:12 PM
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top down/off aero mods that you should do are the same as the top up/on aero mods you should do... top up/on is just better is all...
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Old 07-01-2019, 03:35 AM
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One year at Laguna Seca I decided to remove the hardtop since I was just doing fun laps and I thought it would be nice for a change to be driving around with the top off and getting some ariflow (this is back when it was turbo and usually VERY hot in the cabin). I made no other changes to the wing, etc.
I did one lap and came right back into the pits and put the top back on because the car was so loose in anything mid to high speed. The wing was still doing something, just only about half of what it had been doing with the top on. Since I had the car set up to balance nicely with everything working right, the car just did not work with the wing suddenly handicapped. I suppose I could have cut front downforce by half so things were equally handicapped...
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Old 07-01-2019, 08:36 AM
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To confirm what everyone is saying above- I just run HPDE in a 1.6L turbo car. A few weeks ago I got a hardtop, and also had to turn the boost down for reliability purposes. I did a track night last Thursday, and my lap times were 2.5 seconds faster with the hard top than the previous track day, when I was running with the soft top up and 30-40 extra hp. With the top down, the car is even slower than that.

In short- the hard top is a huge difference to aero. It will make a bigger difference on some tracks than others. If you're just going out for fun, drive with the soft top or topless and enjoy. I've been doing that for three years. But if you want to improve performance, save your money and get a hard top.

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Old 07-01-2019, 12:13 PM
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Originally Posted by Schroedinger View Post
To confirm what everyone is saying above- I just run HPDE in a 1.6L turbo car. A few weeks ago I got a hardtop, and also had to turn the boost down for reliability purposes. I did a track night last Thursday, and my lap times were 2.5 seconds faster with the hard top than the previous track day, when I was running with the soft top up and 30-40 extra hp. With the top down, the car is even slower than that.

In short- the hard top is a huge difference to aero. It will make a bigger difference on some tracks than others. If you're just going out for fun, drive with the soft top or topless and enjoy. I've been doing that for three years. But if you want to improve performance, save your money and get a hard top.
Very interesting. The question relevant to me would be whether a soft top car is faster with the added weight of a hard top (but still soft top) but the improved aero.
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Old 07-01-2019, 12:19 PM
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Originally Posted by Tran View Post
Very interesting. The question relevant to me would be whether a soft top car is faster with the added weight of a hard top (but still soft top) but the improved aero.
I was running the hard top with the soft top still underneath, so worst-case from a weight standpoint. Not even close- aero advantage much bigger than weight penalty.
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Old 07-03-2019, 10:53 AM
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Wow 2.5 seconds is a huge difference between soft top and hard top. I would have expected a big difference with top down vs hardtop but not with it up.
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Old 07-03-2019, 12:00 PM
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I will say, Schroedinger's test of hardtop vs. no hardtop is entirely unscientific. Putting the hardtop on and taking it off has never gained me anywhere near 2.5 seconds, even at Laguna which is a fairly high speed track. If you've got a rear wing that may be a different story as in Ryan's case, but not for a non-aero car.
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Old 07-03-2019, 12:35 PM
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Ed is correct. There were some other potential contributors- for instance I was running a little less tire pressure for the faster laps as well. I'm going to start another thread to try to encourage people to include empirical data.
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Old 07-03-2019, 12:48 PM
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Sure. Different day, possibly different temps, perhaps the lower power gave you more confidence in braking, turning, and accelerating sooner, etc.

When I switch from low boost (about 230whp) to high boost (nearly 300whp) on track. I typically don't go faster right away - have to adjust to new braking zones and throttle applications. Sometimes, when learning a track, I go faster when I go to low boost because I can accelerate smoothly in places I couldn't before.
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Old 07-06-2019, 03:44 PM
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Originally Posted by sixshooter View Post
Splitter and high mounted rear wing will still work fine.
They can still work to some extent, but open top murders the wing. Similar sentiment to ThePass, dramatic loss of rear downforce without a top on.
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Old 07-08-2019, 03:00 PM
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With the primary target being relatively consistent soft top up/down aero, I think the main focus will be underbody bits, and just do a moderate ducktail spoiler.
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Old 07-09-2019, 08:09 AM
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This is actually where i am hoping to balance myself.
I do not plan on doing ***** out racing for times and trophies just rocking up and having some pure rock solid reliable fun with my tinkered bombshell.
So top down aero is where I plan on going.
My current plan is splitter, flat floor diffuser and duck tail spoiler.
How terrible that is to drive quickly in I will have to wait and see.
I have my lip and my duck tail the rest is in the cardboard phase and why i ask so many mounting questions.
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Old 07-09-2019, 09:27 AM
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Honestly for street driving, aero in a miata is more trouble than it is worth. You'll scrape everywhere and have constant headaches from damage due to driveways and speed bumps. And unless you're driving like the king of ********, you're not going to see any benefits from it.

After much experimentation, I ultimately went with no underbody aero, some ducting and 5.5 inch ride height on Xida gs. With stock rear sway and a street alignment. Car is probably leaving tons of time on the table (but I haven't been to the track in years) but more fun without the worrying.

Top down means no wing which means no splitter which raises the question of what you're getting from underbody panels. Either go all in for track aero or don't **** with it at all.
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