Subaru BRZ Aero

[serialk11r]

So by my calculation, just underbody panels would give me less than 1 mpg, so that's clearly not worth it on an already fuel efficient car, since the OEM ones run 300 bucks.

Could underbody panels + diffuser be much more effective though? The diffuser would just be maybe 50 bucks in sheet metal and bolts plus 1 or 2 hours time for drilling and bending stuff, and if that could drop another 0.01 Cd, then the overall cost could be worth it.

I probably will take the car to the track sometime but in the Bay Area there's basically only Sonoma Raceway which is pretty far, so this is going to be 99.5% daily driver.

[jedi_sol]

In order to realize a significant gain with underbody aero, you have to do the entire underside.

I agree with Aerohead

A rear diffuser by itself is useless if the incoming air turbulent.

A middle belly pan is useless if the incoming and outgoing air is turbulent

A front undertray helps a little by smoothing the incoming air... but then it loses it's effectiveness because outgoing air becomes turbulent again.

Just lie underneath your new car for a few hours, you'll get creative in coming up with mounting points

[hayden55]

Actually the japanese scion frs have the underbody panels from the oem as an option. Says with the wing and underbody panels it drops the cd from 0.3 to 0.27. But from what ive heard its a typical jdm part which is expensive and hard to get a hold of. But a picture would help you make one for a fraction of the price.

[serialk11r]

Originally Posted by hayden55

Actually the japanese scion frs have the underbody panels from the oem as an option. Says with the wing and underbody panels it drops the cd from 0.3 to 0.27. But from what ive heard its a typical jdm part which is expensive and hard to get a hold of. But a picture would help you make one for a fraction of the price.

The Japanese Toyota 86 you mean. Yes, 0.27 is the lowest drag configuration from the factory and it still leaves money on the table because that's with no diffuser.

The parts are ~300 bucks shipped, which is I guess not horrible but it's definitely not cheap. It uses a bunch of plastic clips already in the floor pan to attach, but the panels have deep indents to allow it to use those clips. I guess a solution is to drill holes into an aluminum square tube as a bracket on one side and attach coroplast directly to the drive shaft tunnel's edge.

It's a lot of work for a car I'm not even that fond of :/ Still waiting on a midengined 2 seater I like to hit the market, something I can keep forever. Maybe airdam it is.

As for mirrors aerohead, this is all I can find:


280 dollars...yea, forget it lol.

Alternatively I could buy a generic fit for 60 something and make mounting brackets for it, but that's a lot of effort to get rid of the awfully convenient power adjustable heated mirrors.

[jedi_sol]

I've got a few ideas. I'll post them tomorrow at work when I have access to ms paint

[serialk11r]

Oh my, I just realized you can get those cheapo polyurethane stick on "splitters" on ebay for 60 shipped. They go under the front bumper and wrap all the way around, like a half in airdam. I could then use it to mount rubber extensions that go lower if necessary, zero hole drilling needed.

I could just lower the car but these cars are so new throwing out the stock springs would be a waste.

[aerohead]

Originally Posted by serialk11r

So by my calculation, just underbody panels would give me less than 1 mpg, so that's clearly not worth it on an already fuel efficient car, since the OEM ones run 300 bucks.

Could underbody panels + diffuser be much more effective though? The diffuser would just be maybe 50 bucks in sheet metal and bolts plus 1 or 2 hours time for drilling and bending stuff, and if that could drop another 0.01 Cd, then the overall cost could be worth it.

I probably will take the car to the track sometime but in the Bay Area there's basically only Sonoma Raceway which is pretty far, so this is going to be 99.5% daily driver.

On a deep,ladder-type chassis,body-on-frame type vehicle a full belly pan and diffuser would be good for a little over 15% drag reduction.
On contemporary cars however,the automakers have been optimizing the underbodies since the 1970s.
With the BRZ,it's hard to actually predict what a 'clean' belly would do.
If,in the future,you decided to add some rear length,a good belly would make all that work to its full potential.

[aerohead]

Originally Posted by serialk11r

The Japanese Toyota 86 you mean. Yes, 0.27 is the lowest drag configuration from the factory and it still leaves money on the table because that's with no diffuser.

The parts are ~300 bucks shipped, which is I guess not horrible but it's definitely not cheap. It uses a bunch of plastic clips already in the floor pan to attach, but the panels have deep indents to allow it to use those clips. I guess a solution is to drill holes into an aluminum square tube as a bracket on one side and attach coroplast directly to the drive shaft tunnel's edge.

It's a lot of work for a car I'm not even that fond of :/ Still waiting on a midengined 2 seater I like to hit the market, something I can keep forever. Maybe airdam it is.

As for mirrors aerohead, this is all I can find:


280 dollars...yea, forget it lol.

Alternatively I could buy a generic fit for 60 something and make mounting brackets for it, but that's a lot of effort to get rid of the awfully convenient power adjustable heated mirrors.

Formula-1 cars are using a similar mirror.
*The mounting base should be 'blended' though
*The 'rod' should be streamlined
*The mirror's cap should be deepened
*And a little bit of boat-tailed box-cavity behind
Here's a 2-dimensional flow shape which would be good

[jedi_sol]

Front under tray - the frs front overhang is pretty short, so a front undertray should be easy. I see a bunch of pre-existing holes that you can use as mounting points (red stars).



Perhaps you can buy FRS bumper screws, or if that's to expensive, i always use Nut Clips aka "speed clips". You can find these at Lowes or Home Depot



Middle Undertray Front- this is a little tricky because I can't see the clearance from these angles, but here is my suggestion for mounting points.

Green lines are aluminium bars that you can get from Lowes or Home Depot



Middle Undertray Rear - again, i can't make out the clearance, i've made 2 different mounting point versions

Version 1 - use the existing mounting holes for the OEM underbody panels. You'll most likely have to make spacers out of pvc pipe, and you'll have to find screws that fit the threads and are long enough



Version 2 - another possible mounting point (again, depends on the clearance)



Full undertray



*you'll have to get creative for the rear diffuser. I am just making assumptions that the rear suspension and exhaust lies flat (similar to my STI).

Full undertray from the rear

[UltArc]

Definitely underbody. I was looking at the 86GT before I decided on the Mustang, but too many drawbacks. I like a lot of the aspects, and the new models have corrected most of my complaints, so smart to hold out and get into one now.

My only underbody issue has been efficiently dealing with the driveshaft. An idea I learned too late, and that could have really made things easier: think about getting some good after market side splitters. They will mount perfect, and can be an amazing platform for your underbody, cheap and easy ground effects, and simple to work on. To elaborate, you can measure, then do all the work in your house, prep, build, then just install. Foam ground effects within an inch of the pavement, they are scratched and beat up? Much easier to repair when you can remove them!

Haven't looked up the 2015/16 tow capacity, but some big railroad ties and chunks of wood to drive onto them with makes an awesome lift. I did it with 900 pounds of bricks... Easier to return. Also note, a cold start drive that gets 34 mpg becomes 27 mpg with a warm start... And 450 pounds of bricks... Lol