Aero Mods

I can't decide if I took a break from studying earlier or if it just melded into something I was actually interested in. I was studying for a fluid dynamics exam, and got way off track looking up fuel saving aerodynamic modifications. Then it came full circle when I started looking at diagrams and equations as to why they work.

Anyway, has anyone here experimented with these ideas?

I managed to get 29mpg on the highway in my camaro the last tank, and I make enough long trips to savor an extra mpg or two. I was thinking of extending and widening my air dam (also redirects to radiator), adding some gurney flaps around the wheels, and making plugs for some holes in the front fascia.

I initially found inspiration on ecomodding websites, but then my focus shifted to studying how the C5 and C6 vettes manage air, and they have quite a few pieces doing so.

http://www.timeattackforums.com/forums/aero-dynamics/2918-lots-aero-parts-built-my-garage.html

when I put the huge air dam on my CRX I started getting an extra 2mpg on the highway.

I'll be smoothing out the underside and making some sort of rear diffuser in the next 6 months.

Google "ecomod" and you'll find quite a bit about improving your gas mileage with some plastic sheeting and blue masking tape.

besides all the 'standard' mods, how bout the dimpled body?

I saw a Golf on the road yesterday with a roof rack that included 4 flat surfaces to the wind that were at least 4" x 5", plus the cross bars. Just taking that thing off would have saved 2-3 mg!

Raze wrote: besides all the 'standard' mods, how bout the dimpled body?

I think they pretty well proved that didn't do anything. the car would basically have to be designed around a dimpled body, because dimpling caused too many problems, or added too much weight.

pinchvalve wrote: I saw a Golf on the road yesterday with a roof rack that included 4 flat surfaces to the wind that were at least 4" x 5", plus the cross bars. Just taking that thing off would have saved 2-3 mg!

FWIW, if the Golf is a TDI, it may not matter as much as you would think. I see a negligible difference in mileage with or without the roof (bike) rack on my wagon. That said, aero can make a difference on a TDI. There's a guy on TDIclub with a aero-modded Jetta and regularly gets in the upper 50's driving @ 80+ most of the time (engine is also modded). Some of his mods are a bit extreme in my opinion - such as removing the passenger side mirror.

Many front air dams on performance cars are there as much for directing air-flow into the radiator as they are for any other reason. Especially on a Vette where there is little to no grill to speak of.

As far as adding a rear diffuser to the underside of your bumper, is the difference really worth the effort? I drive a sedan, and have been thinking about adding something like the first pic on this thread, as well as a trunk lip spoiler to help reduce drag that sedan bodies make. Whats my best bang for the buck that doesnt make me look like a F&F fan gone wild?

Some very cool stuff in that link, thanks for posting!

4cylndrfury wrote: As far as adding a rear diffuser to the underside of your bumper, is the difference really worth the effort? I drive a sedan, and have been thinking about adding something like the first pic on this thread, as well as a trunk lip spoiler to help reduce drag that sedan bodies make. Whats my best bang for the buck that doesnt make me look like a F&F fan gone wild?

I'm kinda in the same boat. For some reason or other the rear bumper cover on my car hangs down a good 6" below the floor, like a giant parachute back there. Been toying with doing something with that for a while but have no idea where to start...

How about mileage improving aero mods for my GMC Sierra 2500? Now that thing could really use some help!

thestig99 wrote: Some very cool stuff in that link, thanks for posting!

4cylndrfury wrote: As far as adding a rear diffuser to the underside of your bumper, is the difference really worth the effort? I drive a sedan, and have been thinking about adding something like the first pic on this thread, as well as a trunk lip spoiler to help reduce drag that sedan bodies make. Whats my best bang for the buck that doesnt make me look like a F&F fan gone wild?

I'm kinda in the same boat. For some reason or other the rear bumper cover on my car hangs down a good 6" below the floor, like a giant parachute back there. Been toying with doing something with that for a while but have no idea where to start...

There's a lot of aero to be gained on the bottom of the car. Making it flat and a diffuser maybe not so useful, but making it flat will be.

One of the reasons front spoilers work so well is that the flow under the car is so bad- reducing it helps a lot.

bravenrace wrote: How about mileage improving aero mods for my GMC Sierra 2500? Now that thing could really use some help!

bed cover, tailgate net or bar gate = big improvements

Why is it that I don't see tailgate nets anymore? I'm thinking of getting one on my Sonoma, since the tailgate is rusting apart.

bravenrace wrote: How about mileage improving aero mods for my GMC Sierra 2500? Now that thing could really use some help!

One of the really entertaining things about ecomodder or gassavers is the high volume of full sized pickups and vans that people are modding for fuel efficiency:

Picked the first one.... http://www.gassavers.org/showthread.php?t=11906

RoosterSauce wrote: Why is it that I don't see tailgate nets anymore? I'm thinking of getting one on my Sonoma, since the tailgate is rusting apart.

My dad has one like above. He never uses it as a tailgate anymore since it's sort of flimsy and it gets in the way preventing the truck from being able to back up right next to something. So you pretty much have to lift everything over the tailgate thingy and set it on the bed. It's awful.

I think the mythbusters episode with the ford truck pretty much put the nail in the coffin for nets. Seems they generalized that since they didn't help on that truck it wouldn't help on any truck, and most people went with that. I'd argue that each truck body is different and it might help a lot in one and none in another, but what do I know?

Classic aero includes salt flat discs and smaller mirrors, might start there with pretty much anything.

alfadriver wrote:

thestig99 wrote: Some very cool stuff in that link, thanks for posting!

4cylndrfury wrote: As far as adding a rear diffuser to the underside of your bumper, is the difference really worth the effort? I drive a sedan, and have been thinking about adding something like the first pic on this thread, as well as a trunk lip spoiler to help reduce drag that sedan bodies make. Whats my best bang for the buck that doesnt make me look like a F&F fan gone wild?

I'm kinda in the same boat. For some reason or other the rear bumper cover on my car hangs down a good 6" below the floor, like a giant parachute back there. Been toying with doing something with that for a while but have no idea where to start...

There's a lot of aero to be gained on the bottom of the car. Making it flat and a diffuser maybe not so useful, but making it flat will be. One of the reasons front spoilers work so well is that the flow under the car is so bad- reducing it helps a lot.

I added a coroplast (corrugated polypropylene sheet) belly pan to my 96 civic in the interests of efficiency and performance. It covers 60-70 % of the bottom of the car including the nose up to the middle of the motor.- these pics are not that good, but it is much smoother than the OEM surface and is much much closer to being 1 flat plane. It cost 40 bucks or so and went in with self tapping sheet metal screws, washers, a few rivets, and zip ties in an afternoon. I picked up a mpg or 2 at freeway speeds but the really interesting part for me was how much more settled the car was in wind and truck wakes. The little motor also had very noticeably easer time getting the car up to 90-100. The faster I go the better it works. New cars are getting this sort treatment much more regularly.

http://www.gassavers.org/garage_images/6mmyxhg3tiib6cghkn1m.jpg

http://www.gassavers.org/garage_images/rcklpw87mku3kwtlqdvm.jpg

4cylndrfury wrote: bed cover, tailgate net or bar gate = big improvements

Not that they're the definitive source, but when the Mythbusters tested this they found that having the tailgate down dropped fuel economy, a bed cover was about the same as an open bed with the tailgate up, and a tailgate net was good for as much as a 5% improvement. Of course, YMMV.

oldopelguy wrote: I think the mythbusters episode with the ford truck pretty much put the nail in the coffin for nets. Seems they generalized that since they didn't help on that truck it wouldn't help on any truck, and most people went with that.

They didn't test tailgate nets with the F150's, just tail gate up and down. When they re-tested with Dakotas and added bed covers and tailgate nets, they found nets to be the best option.

Shaun wrote:

alfadriver wrote:

thestig99 wrote: Some very cool stuff in that link, thanks for posting!

4cylndrfury wrote: As far as adding a rear diffuser to the underside of your bumper, is the difference really worth the effort? I drive a sedan, and have been thinking about adding something like the first pic on this thread, as well as a trunk lip spoiler to help reduce drag that sedan bodies make. Whats my best bang for the buck that doesnt make me look like a F&F fan gone wild?

I'm kinda in the same boat. For some reason or other the rear bumper cover on my car hangs down a good 6" below the floor, like a giant parachute back there. Been toying with doing something with that for a while but have no idea where to start...

There's a lot of aero to be gained on the bottom of the car. Making it flat and a diffuser maybe not so useful, but making it flat will be. One of the reasons front spoilers work so well is that the flow under the car is so bad- reducing it helps a lot.

I added a coroplast (corrugated polypropylene sheet) belly pan to my 96 civic in the interests of efficiency and performance. It covers 60-70 % of the bottom of the car including the nose up to the middle of the motor.- these pics are not that good, but it is much smoother than the OEM surface and is much much closer to being 1 flat plane. It cost 40 bucks or so and went in with self tapping sheet metal screws, washers, a few rivets, and zip ties in an afternoon. I picked up a mpg or 2 at freeway speeds but the really interesting part for me was how much more settled the car was in wind and truck wakes. The little motor also had very noticeably easer time getting the car up to 90-100. The faster I go the better it works. New cars are getting this sort treatment much more regularly. http://www.gassavers.org/garage_images/6mmyxhg3tiib6cghkn1m.jpg http://www.gassavers.org/garage_images/rcklpw87mku3kwtlqdvm.jpg

Very cool. How strong is the stuff? My concern would be durability being under a fairly low car that gets driven hard. I was mainly thinking about doing something where the front lower splash shields used to be (possible extending that out to double as a splitter?) and then smoothing out the rear bumper/spare tire well area.

bravenrace wrote: How about mileage improving aero mods for my GMC Sierra 2500? Now that thing could really use some help!

google search ecomod T100.

4cylndrfury wrote: As far as adding a rear diffuser to the underside of your bumper, is the difference really worth the effort? I drive a sedan, and have been thinking about adding something like the first pic on this thread, as well as a trunk lip spoiler to help reduce drag that sedan bodies make. Whats my best bang for the buck that doesnt make me look like a F&F fan gone wild?

I have studied ground effects a bit recently. They will increase downforce and drag. How much downforce and drag is produced is determined by how long the flat section is. The long the throat is the more downforce and more drag will be produced provided seperation does not happen in the diffuser.

oldopelguy wrote: I think the mythbusters episode with the ford truck pretty much put the nail in the coffin for nets. Seems they generalized that since they didn't help on that truck it wouldn't help on any truck, and most people went with that. I'd argue that each truck body is different and it might help a lot in one and none in another, but what do I know?

I agree. It does seem to be body-dependant. I think any additional items in the bed can play a part as well. On my old 86' Toyota 4x4 std cab, there was a noticable difference with the gate up or down - on long trips, I could literally feel the difference in how much effort I had to put on the gas pedal to maintain speed. However, I also had a tool box in the bed that changed the air flow through the bed, so there was less of the vortex effect that MB saw and the gate acted more like a wall. When I added a fiberglass cap, mpg improved even more. It seems the aero improvement out-weighed the additional weight.

I've never tried driving my Cummins with the gate down. That truck doesn't need to be any longer... I regularly haul too much 'stuff' to be able to install a net in place of the gate.

thestig99 wrote: Very cool. How strong is the stuff? My concern would be durability being under a fairly low car that gets driven hard. I was mainly thinking about doing something where the front lower splash shields used to be (possible extending that out to double as a splitter?) and then smoothing out the rear bumper/spare tire well area.

I have been pleasantly surprised at the durability. I did do a good job of putting it in there, the self tappers are 1/4 20 and pre drilled with the right sized bit to leave the threads some metal to hang on to, and I made sure the leading edges tipped up so air, rocks, rabbits, and the like would not have a clear wedging path. I have ground it into rocks several times on dirt roads while fly fishing/camping and made it into triple digits a couple times with no attachment point failures or flapping. It is a little beat up but the stuff is really quite tough. 2 years old now. I did an hours hours worth of maintainance last weekend- added 4 self tappers and a couple more rivets to snug it up a bit for the deluge. It has about 20-25k on it now.

If you go for it, think carefully about where you are going to be putting self tappers or rivets. Some cars may not provide as much suitable void area for drilling into the floor pan as this civic does. The civic has plastic rocker panels that wrap under and are attached with 3/16 ish rivets. I drilled out the rivets, slid the coroplast in, drilled the coroplast, and riveted the rocker back up with the coroplast sandwiched in.

In reply to Shaun:

Where do you get the coroplast? I wanna do an undertray on my NA miata as the stock one is kinda mangled and it seems like a fun project. I've also seen the rally guys use hdpe sheets, but that's more for impact protection than aero.

I like ecomodder.com for aero research.

i address just this topic this past winter the best i could with what resources i had at the time. i also choose to use the coroplast for my underpanel. i welded studs to the tops of some bolts on the undercarriage i then drilled holes in them so that i can slide my underpanel over and secure with hair pins. i can reach these hair pins for the rear of the underpanel while the car is on the ground. i also sealed off the front bumper and than made ducting to the radiator. i run a single 18 panoramic convex rear view mirror that gives me a better field of view than previous 3 mirror combination. lastly i painted the car with texture to help make a thinner boundary layer. a couple years ago i was averaging 34 mpg on the obc. since than i have addressed the aero i mention above and removed another 500+lbs; i expect ~40mpg just havent checked it since on the road. as other have mentioned aerodynamics are worth far more than weight depending upon the speeds the vehicle will live at. heres a calculator is stumbled upon http://www.gtechprosupport.com/support/AeroDragCalc.htm this winter i want to actually make extraction ducting out my hood for the radiator which i will have to mount at an angle. i also removed the spare tire well and added a flat piece if sheet metal with some bead rolling for added rigidity. i moved my battery box up a couple inches too. i do not run a rear bumper and would like a help keep the air attached as it comes from under the car and around the rear fenders; maybe this winter =/