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Old 05-02-2012, 04:04 AM   #21
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Or this



Sorry but mounting it completely below the stock bumper, with no other mods, is fail. Trim the bumper and tuck it up in there. More ground clearance and more downforce. Double win.
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Old 05-02-2012, 07:30 AM   #22
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Thank you mobius for demonstrating with photos what I was trying to convey!
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Old 05-02-2012, 08:57 AM   #23
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I don't think there's anything wrong with it being lower to the ground, in fact, with the remainder of the under-body aero sorted, it's better to have it as low to the ground as possible to prevent air from being sucked in from the sides. There's plenty of examples of race car aero running similar rear diffuser setups, that strive to get low to the ground as possible. The difference being they have a completely flat underbody leading up to it.

I understand higher is better if the purpose of the diffuser is to replace the parachute effect of the rear bumper, but then you may as well not run a rear bumper at all/cut lower half of bumper off.
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Old 05-02-2012, 09:16 AM   #24
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You should have put that $600 into a slush account for turbo instead. Just my $0.02.
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Old 05-02-2012, 10:58 AM   #25
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second. I cant prove that it doesn't work but is really looks silly imo. all you can do is take laptimes with segment info to see whats going on with that thing. if it works it works.
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Old 05-02-2012, 01:33 PM   #26
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Hey guys, just a thought here. If I remember correctly there have been some discussions by some of our more intellectual minds, on how much actual drag is caused by the stock bumper. Someone was going do do some roll down test if my memory serves me right. It seemed to be undetermined. I'll try to look up some of the posts when I have time later.

I'm not a fan of form over function, and I'm certainly not a guru, but if this kid doesn't want to hack up is bumper, wouldn't all or most of the air entering the "parachute" be eliminated with a proper under tray. Something that could be easily removed if he wanted to return the car to stock to sell it? I'll have to admit it's been quite a while since i've read any of those diy splitter threads, but if the under tray meet up with the diffuser in a smooth transitions wouldn't the lower diffuser actually be better, as long as the AOD was correct?

Flame away if I'm wrong, just thinking out loud.

Edit: Just wanted to add. I realize it's not optimal, but what I'm asking is HOW bad is it if it had a proper underbody? I think most of us here make concessions with our cars. Either because a lack of funds, or wanting to keep it street able. We don't do things the "proper" way, we make it "good enough" for our situation.

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Old 05-02-2012, 02:01 PM   #27
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I think that's really the most funny thing about the input...

the bumper is hacked, I mounted the diffuser where i wanted it, the leading (front) edge even with the floor of the passenger compartment, and the rear was placed as so the fins would be parallel to the ground, the i cut the bumper as much as i needed to, It's has the cutout for a "dual" exhaust then another 5 inches from the top of the cutout inward, as well as about 2-3 inches along the entire lower edge between the outer elements.

IMO this is the optimal position for this diffuser, it wasn't placed where it is for looks at all. I'm sure it's easy to call anyone that would make this type of modificaion a "ricer" or "form over fuction", i don't think i'm either of those, it's mounted where it should be.

Raising it up would do 1 of two things, or a combination of the both.

1.You can lift the entire diffuser up vertically and there would then be a step from the rear lower arm/diff and the diffuser causing a huge amount of turbulent air just as the air is entering the diffuser.

2. you can raise just the rear of the diffuser, making the fins no longer parallel to the ground. Raising the angle of the diffuser to an un-ideal point. like said before the center sections are at 10 degree and the outer are at 20, raising the rear of the diffuser as high as possible would make those more like 40 and 50, any air going over is going to separate from the diffuser and cause the air coming out of the the back of the car to be as turbulent as not having a diffuser at all.
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Old 05-02-2012, 02:12 PM   #28
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I think you need to post up some pics of this thing from under the car.

At first glance it does look like you just slapped it underneath the bumper. Showing the details of exactly how its mounted may save your case.
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Old 05-02-2012, 02:19 PM   #29
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Mounted on the same height/plane as the floor of the car...this picture's on the first page.
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Old 05-02-2012, 02:41 PM   #30
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Quote:
Originally Posted by viperormiata View Post
you just added more drag. The stock bumper is a parachute. You need to cut into the stock bumper and raise the diffuser.

Think this:
this!
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Old 05-02-2012, 02:48 PM   #31
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Quote:
Originally Posted by FTNguyen View Post

Mounted on the same height/plane as the floor of the car...this picture's on the first page.
Unless you have the entire bottom of the car sealed at the level of the red line, there's air above it. The pinch panels are below the floor of the car by 1-2", and the transmission tunnel and subframe bracing is another 1-2" above that. What you end up with is a big gap that gathers air above the diffuser and stuffs it into the bumper.

With a diffuser that big, you should be able to feel a big, big effect.

BTW - wings on a Miata do almost nothing without a hardtop. If you don't have smooth airflow to aero features, there's almost no point in having them at all.
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Old 05-02-2012, 03:07 PM   #32
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Quote:
Originally Posted by Savington View Post
Unless you have the entire bottom of the car sealed at the level of the red line, there's air above it. The pinch panels are below the floor of the car by 1-2", and the transmission tunnel and subframe bracing is another 1-2" above that. What you end up with is a big gap that gathers air above the diffuser and stuffs it into the bumper.
the frame rails are lower then the pinch welds, thus if you want a true under panel you'll need to go at least to the frame rails...that's a project for later.

the first picture of a mount is where the lowest part of the diffuser, it's less than 1 inch below the mounting surface of the rear subframe brace brackets. the red line doesn't necessarily depict that point as you can still see some air gap behind the rear tire.

Quote:
Originally Posted by Savington View Post
With a diffuser that big, you should be able to feel a big, big effect.
I never push this car on the streets, i can say it feels better, at least i think it does...i'll be back at the track in the next few weeks we'll see how speeds are affected, both in turns and straight speeds from all the drag i created.


anyways no real point to argue this further, it's where it's supposed to be, although i'm sure you're all experts and Adrian Newey has you on speed dial.
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Old 05-02-2012, 03:30 PM   #33
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Make crappy car modification.

Call everyone haters for disproving it.
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Old 05-02-2012, 03:33 PM   #34
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keyboard aerodynamicists....call ricer...
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Old 05-02-2012, 03:36 PM   #35
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Quote:
Originally Posted by FTNguyen View Post
keyboard aerodynamicists....call ricer...
Yes, we are all ricers on this board. None of us have track cars or no anything about racing cars at all.

Don't get mad at us. You need to tuck the diffuser higher into the bumper. It can be done easily. I would do it simply so you don't rip that nice diffuser off the car when you go off course or over a speed bump.
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Old 05-02-2012, 03:38 PM   #36
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yes i don't race at all..........this is my first miata not my first "race" car.

negatively adjust aero work so that you can go over speed bumps, and go off track.

although i think i can go off track just fine as is...
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Old 05-02-2012, 03:45 PM   #37
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Quote:
Originally Posted by viperormiata View Post
Yes, we are all ricers on this board. None of us have track cars or no anything about racing cars at all.

Don't get mad at us. You need to tuck the diffuser higher into the bumper. It can be done easily. I would do it simply so you don't rip that nice diffuser off the car when you go off course or over a speed bump.
Do you have significant personal experience on-track, testing various aero setups? Or are you just repeating what you've seen/heard/read on the internet?

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Old 05-02-2012, 03:50 PM   #38
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Quote:
Originally Posted by FTNguyen View Post
anyways no real point to argue this further, it's where it's supposed to be, although i'm sure you're all experts and Adrian Newey has you on speed dial.
I could spend time discussing why you need to move/change it, but it's clear that you have no interest in actually improving your setup, so I'll just leave you to it.
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Old 05-02-2012, 05:03 PM   #39
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FTN,

If possible I'd like to see some shots from underneath to see how you mounted it
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Old 05-02-2012, 05:14 PM   #40
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