thehatchninja

This is somewhat inspired by the VX air diffuser, and the fact that my splashshield ripped off. Last time I was under my car I noticed a lot of gaping holes for wind to get caught in. So I figured I'd research the fab section to see if anyone has closed up those holes with sheetmetal.

disclaimer: I know a street car would benefit very little from this, and that my car is not a track car. I just think it would be freakin' sweet. THANKS

troubledsol03

I thought about that too using a sheet of thin gauge aluminum under the car to help eliminate drag

I think it would help gas milage and all forms of racing just my $0.02

driveahonda

I am planning on making one to cover most of the under side pretty soon.

I'm sure it will only have positive effects to the cars handling, mpg, speed, etc.

AccidentproWn

I've been contemplated doing this same project with fiberglass.

thehatchninja

i'll def. be doing this before september when i start my cross country road trip.

has anyone done this, or have any pics/liinks????

DavidR

take a look at a Lotus elise, it comes from the factory with a full underbody cover.

nfn15037

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by driveahonda &raquo;</TD></TR><TR><TD CLASS="quote">I am planning on making one to cover most of the under side pretty soon.

I'm sure it will only have positive effects to the cars handling, mpg, speed, etc.</TD></TR></TABLE>

You're pretty sure? Improper aerodynamics can have dire consequences at high speeds. You had better be very sure before you go and turn your car into a lift-machine. All of those OEMs and race teams with pimpy underbody aero have/use wind tunnels to develop specific angles of attack and such. You, I feel, do not.

Mr.E.G.

what kind of car are you guys planning on doing this to? are you wanting downforce, or just reduced drag/ eleminating some of the positive lift that our cars have from factory?

have you thought about where the warm air from your radiator will go?

lets see some underbody pics

driveahonda

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nfn15037 &raquo;</TD></TR><TR><TD CLASS="quote">

You're pretty sure? Improper aerodynamics can have dire consequences at high speeds. You had better be very sure before you go and turn your car into a lift-machine. All of those OEMs and race teams with pimpy underbody aero have/use wind tunnels to develop specific angles of attack and such. You, I feel, do not.</TD></TR></TABLE>

Straight line racing... covering a portion of the back half only...

Starting to feel where I am going with this buddy buddy?


PS: I never said pretty.

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nfn15037 &raquo;</TD></TR><TR><TD CLASS="quote">You're pretty sure? Improper aerodynamics can have dire consequences at high speeds. You had better be very sure before you go and turn your car into a lift-machine. All of those OEMs and race teams with pimpy underbody aero have/use wind tunnels to develop specific angles of attack and such. You, I feel, do not.</TD></TR></TABLE>

designing a good underbody is not that hard. it takes time and testing to really optimise it, but if your goal is just to improve the underbody versus stock, then it is not at all challenging. from factory our cars make positive lift at high speeds. simply by smoothing out the underbody we can alleviate most of the positive lift. just keep the rake lower in the front.

for the record, i happen to know a little about this sort of thing and if you guys want to do this i would be more than happy to make some suggestions.

RPRacing

now i heard that smoothing the underbody only helps at high speeds. is this correct? or does this jsut amplify as the speed goes up?

Mr.E.G.

anything aerodynamic will only matter at high speeds. i have to run, i will elaborate tomorrow

Mr.E.G.

ok, im back. i will keep this simple with general statements so dont break my ***** if i over generalize.

aerodynamics only really become an issue at high speeds. but to say that it doesnt matter on street cars doesnt really make any sense because highway speeds are certainly (and obviously) high enough to feel the effects of our cars interactions with the air that they are passing through. i personally think that it is kind of a waste to try and make a lot of downforce through underbody modifications on a car that you will only be drivng around at legal speeds. to make a lot of downforce you really need a suspension setup that can work with the load that it has at low speeds and no downforce as well as the ability to work well at levels of high downbforce. but i think the idea of eliminating the positive lift that most factory cars have is a good idea. you arnt really asking for too much, you are just removing some of the negative which will help you at high speeds.

i could go on for hours here, so i will stop my self and say that if you have a particular goal, say the word and i can offer specific advice.

thehatchninja

here's a particular goal.....improved gas mileage on my daily driver....a little more stability when i accidentally get into a street race, or just decide to drive over 100 (on an empty highway with wall barriers on each side.....on Mars)

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thehatchninja &raquo;</TD></TR><TR><TD CLASS="quote">here's a particular goal.....improved gas mileage on my daily driver....a little more stability when i accidentally get into a street race, or just decide to drive over 100 (on an empty highway with wall barriers on each side.....on Mars)</TD></TR></TABLE>

ok. will you still need the hot air from the ridiator to escape through the bottom of the engine bay or do you have a vented hood?

sorry to go bak and forth, but i am going to draw something up and this could negate it.

Niles

The undertray is a good area to reduce lift. This we all agree on. I think shooting for a zero lift shape is a good goal. (The g35 made a big deal about a 'zero lift' underbody aero package a while back. Shown to increase stability and reduce drag. Ideas for tweaking the OEM shape could come from there)

This doesn't mean creating any downforce. There are quite a number of books written on car chassis aerodynamics, check out amazon to help develop your ideas and decide what's doable.

As a side note, in most states that aren't Ohio, where the cops WILL enforce and pull you over for doing 65 on a highway, or california, where there's so much congestion the fastest you go will be in your driveway, you'll find alot of cars have a front end that gets light at legal highway speed. Look under the front of alot of GM cars and you'll see a flexible air dam that was fitted to fight the problem (When I worked for a gmc/olds dealer I noticed the olds intrigue and aurora for example have these dams. when they get torn off on curbs, people complain of highway instability.) Anyway if you're willing to put in a bunch of effort for a few points off your Cd, I say go for it. If nothing else you'll have a fun project and learn alot.

Good luck.

snoochtodanooch

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nfn15037 &raquo;</TD></TR><TR><TD CLASS="quote">

You're pretty sure? Improper aerodynamics can have dire consequences at high speeds. You had better be very sure before you go and turn your car into a lift-machine. All of those OEMs and race teams with pimpy underbody aero have/use wind tunnels to develop specific angles of attack and such. You, I feel, do not.</TD></TR></TABLE>

I agree with you, can you say lift?

Kevin

If you research your design, it can be effective without a wind tunnel or worry about creating lift but you definetly need to understand basic aerodynamics. The shape is the most important part, you do not want the back of it to hang down and create lift.

Im just making a small undertray from the front lip to the front of the motor, simliar to a lot of a oem trays. I thought about making it all the way to the firewall but i dont think its necessary on my particular setup. On my project im letting the undertray stick half an inch out of the bottom of the lip all the way around. This ties the undertray, front lip & front bumper together for strength, the 1/2" lip provides a little extra downforce. I havent figured out how im going to vent it but i want to make some louvers that direct air from the bottom of the car into the engine bay. Not too big but enough to get airflow into the engine bay and perhaps provide a little more downforce as well.

I made a quick paint image of what im trying to accomplish.

driveahonda

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gLok &raquo;</TD></TR><TR><TD CLASS="quote">
</TD></TR></TABLE>


What kind of car is this?

Kevin

Its not a type of car, its just a generic shape to show what i was talking about.

paulzy

iTrader: (1)

look kinda like a dodge daytona to me

Mr.E.G.

not trying to be a dick, but where exactly is the air going to go once it enters you "vents" in the underbody? my point is that if you make a lip like that and an undertray etc, the pressure under that part of the car will be low and therefore your vents will be working backwards. the air across the radiator needs to flow from high pressure to low pressure and the whole idea behind creating underbody down force/ reducing underbody lift is keeping the pressure beneath the car low by letting the air accelerate (remember, the faster the air moves, the lower the pressure).

so first things first, make a front lip to limit the amount of air that goes underneath the car. a good deal of underbody drag as well as underbody induced lift comes from the engine bay on civics (which is what i assume we are talking about here) when the air goes form wide open space, to being "squeezed" through the section between the bumper and the road, it will then expand and therefore slow down once it hits the big open cavity of the engine bay. blcoking off the engine bay is a great start but you still need to consider where the air that blows across your radiator will go. a vented hood will do the trick, but if you've got the room under the hood (which most front wheel drive cars dont) you can have the air enter the front of the radiator like normal and then have special duct work route it through the hood so that it never bounces around and interferes with the engine.

my best advice is that you keep the front angled lower than the rear. in the very front a low hanging air dam and possibly a protruding lip parrallel to the ground. make sure it stays smooth all the way back from the lip to the back of the engine bay. you can enhance this a little further with a simple front diffuser. maybe i should go draw something real quick, ill be right back.

ok i modified your car pic a little to show kind of an ideal setup, which isnt necessary on a street car, and which unless you have an s2000, you probably dont have enough free space for some of this stuff, but either way this is a little more ideal



please notice the front diffuser. the idea behind this is that it lets the air slow back down just a little behind the front wheel which will turn the undertray area prior to that into a venturi with a smooth transition which will make a good deal of downforce right under the front wheels which is where you would want it on your fornt wheel drive car. in this pic i made the front rdaiator vent through the hood using ducting to guide the air, but a slightly less ideal but more practical way is to just have a vented hood.

Kevin

I think you went a little too far with your explanation. This is just for a street car and doesnt need to be that extreme. The vents i explained in my drawing are similiar to those found on stock vehicles. Im not talking about huge scoops bringing air into the engine bay causing a pressure buildup. Not to mention my hood is already spaced on the rear to allow air to escape.

Niles

The area at the base of the winshield tends to be not only high pressure (relatively) but also on some cars its somewhat stagnant. Venting a hood here is, on most cars, innefective. In fact you see hotrods with intake air scoops here to take advantage of the increased pressure. The usual place that functional vented hoods are vented is between the front and middle of the hood, as this location will help air escape.
Remember that running a front air dam/splitter will force MORE air to go through your radiator as it has nowhere else to go, and you'll need to account for that. Running a diffuser angled too steep can cause undue flow separation and increased drag/increased lift. "Too steep" If is probably 20 degrees. 15 might even be pushing it, If I find any articles referencing diffuser angle I'll post some references.

Mr.E.G.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Niles &raquo;</TD></TR><TR><TD CLASS="quote">The area at the base of the winshield tends to be not only high pressure (relatively) but also on some cars its somewhat stagnant. Venting a hood here is, on most cars, innefective. </TD></TR></TABLE>

i agree. the top of the hood venting method is releasing the air into a lower pressure area. the windshield area will have a good deal of pressure built up on it.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gLok &raquo;</TD></TR><TR><TD CLASS="quote">I think you went a little too far with your explanation. This is just for a street car and doesnt need to be that extreme. </TD></TR></TABLE>

i realize that my drawing was a bit extreme and not ideal for street cars, but i was just showing a best case scenario and you can take away the elements individually and use what will work best for your application.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by gLok &raquo;</TD></TR><TR><TD CLASS="quote">The vents i explained in my drawing are similiar to those found on stock vehicles. </TD></TR></TABLE>

thats exactly my point. stock cars have **** *** underbody aerodynamics. they choose to let radiator air blow out of the bottom for packaging reasons and this is no bueno for aerodynamics. i am not trying to be a smartass or anything and im not trying to tell you you're wrong but your vents arnt really doing anything. there are plenty of cars (think mid engined) that have no airflow blowing across the engine itself. your main focus should be getting air through the radiator and out of the engine bay and then more or less closing off the engine bay. in your drawing you show the air entering from the underbody but i cant see why you would want that to happen.

i think a closed engine bay is the bast way to go... now to contradict myself a little, its all about compromises and ther are someinstnaces where you will need to let the air tat blows across the radiator vent though the bottom of the engine bay since it has to go somewhere. you can meet in the middle and block off the majority of the engine bay and then make vents sort of like the ones you had in your picture only they would be working in the opposite direction. obviously they would effect the underbody airflow, but the only thing worse than having poor underbody airflow is having your engine overheat




this is a mugen undertray for the honda fit. they have vents like i just described. again, this is a compromise and the car will perform better with this smooth underbody and all of its integrated downforce producing devices, however it would be more efficient if the air that blows acorss the radiator never saw the undebody of the car.

again, i am not trying to sound like a dick or anything, but i happen to know a quite a bit about aerodynamics, and i can say that this is a subject with a lot of misconceptions