Body and under body mods for a Track Spec Hatch

[gtpornstar]

Looking a bit of info on what works for a hatch interms of its aero dynamics and mods to it.

Looking at the following

Front splitter
Front Canards
Winglets
Rear diffusser
Rear Wing

Any help appreciated

[gtpornstar]

are the honda boys more on to it than we are

[frost]

there more onto it cos they think its going to help them, unless your constantly above 100kmh all that stuff is not going to help AT ALL,

you can tack on as much wings, Canards and etc, but unless you have track testing producers to see how effective they are, your wasting your time,

a hatch is a terrible shape for aerodynamics to start with. 99% of those aero parts sold for honda civics are "wank factor items" they will increase drag on the car,

front splitter must be atleast 20cm infront of bumper for it to be effective (think of the old V8 supercar ones)

and a rear diffuser is no use unless 3/4 of the undercarrage is flat leading to the diffuser, then you will need side skirts to stop air escaping out the side,

canards are only useful if you have wide body and need to direct air over and around the front wheel archs,

rear wing on a hatch is just silly,

oh what car is it for?

[20v_rollaboy]

I presume its for his Glanza.

[frost]

oh i see you said track spec hatch, my bad for skim reading,

here is some pics of the diffuser
http://www.pennon.com/products/diffusers/diffusers.html
its for a f2000 but the principles are the same, the ramp angle above horizontal should be between 7-12degrees and at least twice its length of flat run area before the start of the diffuser, and full side skirting will be need to for it to be effective,

dont take off the bottom engine bay tray, infact try to make one that can seal better then factory, but this can cause hotter engine bay temps,
a flat front tray will make a low presure spot,

airdam on the front of the car will help make low pressure under car,

and a front splitter can increase front down force by alot, but can look quite ugly being so long in the chin, if you can integrate the engine tray with the splitter(one single peace) this will stop air going under the car by alot also, resulting in heaps of down force, dont make the splitter horizontal but slightly angled up, when at speed it will sag down heaps and touch the road,

i dont think you should put stuff ontop of the car. this will only increase car drag coefficient, you should try and stop air from going under the car. try and make the undercarriage as flat as possible, low pressure air will suck the car down onto the tarmac,

first step should be front airdam and splitter,
dont worry about carnards/dive plates yet, its too JDM right now,

[gtpornstar]

Yeah its for the glanza. thanks.
I was probably more interested in what to do for a front diffusser (Which is what i was told made the most difference) but also didnt want it to get too much downforce in the front only. As it is at a track like puke the car doenst sit too well on the high speed corners, wants to drift a little.

For the front splitter, yeah was hoping it would protrude back, but wasnt sure how far back, also any pont to making the front 20cm or so hinged and adjustable ? when you say angled up, do you mean looking at it side on from the front axle to the front it should be somewhat angled up, like 10degrees or so ? I also assume there is not much point going 20cm on the sides of the front bumper ? just the front of it ?

With the glanza there is about 1/2 the car somewhat flat but the problem is the rear axle and sending air back up, also my understanding the rear dffusser is doing two things, one is directing air up which is the angle u talk about. the other is direction of air to the middle. is this to keep the rear in line more and stop it sliding around somewhat ?

Airdam meaning a lower bumper front to get more air up and over the car ?

Rear wing, yup not looking to do on top like the yellow civic hehe but more like the red jazz ? below which is a little back of the hatch but in like with the roof, but not sure how wide to go etc.

Thanks a lot for your help, have been a lot of help !

[Bazda]

I would prob not bother with wings at this stage.

You need to work on suspension setup.

Wheel alignment plays a big part in the rear handling of a fwd car. If you find its drifting you need to put a bit more toe in.
Sometimes more rear camber helps alot as well.
When I put more rear camber on mine the back became alot more stable. I tried to put 0 toe on the rear and the back was loose, had to run around 1.5mm toe in on the rear.

Also you have the front track really wide with your spacers, and the back is narrow, that prob doesn't help with the drifting thing.

After playing with toe settings, spring rates are the next ones to play with.

Also, I have found a bolt on caliper for your car which would mean you can get rid of some of that spacer you have.

[XSDRIFT]

+1 on suspension set-up being top priority. You will find that a lesser powered car will still be faster around the track if its suspension is right. Any joker can accelerate in a straight line, but if they can't take the corner at the speed you can its all made up in a matter of seconds.

DEFINATELY don't remove the under engine plate/cover, this helps the cooling and aero of the car.
It is possible to improve it but you will want to get a pressure sensor/meter so that when you adjust things you know if its positive or negative.
Alternatively you can also play with fans and smoke to see where the airflow gets caught or what will happen to air hitting the car.

Rear wing - If you are over 80K these start to have a minimal effect, much greater at say 140K. If you find the rear is loose in corners at speed I would look at this but not before. Also do your research as a lot of spoilers out there work like an air brake just as much as a spoiler so you can end up hurting all the work you are aiming to do.
EDIT: Just noted your comment about the high speed cornering. Probably worth doing the spoiler in that case. Just keep it streamline.

[Adoom]

Rear wing, yup not looking to do on top like the yellow civic hehe but more like the red jazz ? below which is a little back of the hatch but in like with the roof, but not sure how wide to go etc.

I think the wing width is restricted to the width of the rest of the car...... not positive, have to check Schedule A.
Allan Stanniforth's Race and Rally Car source book has a lot of info about aerodynamics for racecars. Biased towards singleseaters though, but still interesting.

But +1 for suspension and sticky tyres FTW!!!

[Bazda]

Yep def avoid aero.
Look at Brett Ingrams Red starlet used to race in SS2000. That handled crazy well, and it had no aero.

[fxgt race]

The rear of my car was a hand full so i made this little spoiler on the back, made all the difference on cornering speed. And the front splitter i made from 4 mm ply, need to do research on splitters as its about shape to cause low and high pressure zones to suck the front off the car down . You don't want to go to big on the back as it will slow you down on the straights, speaking from experence as i had a bigger one on the back and lost 300rpm down the back straight of puke.

[Mr Revhead]

Yep def avoid aero.

why the hell would you do that?
Yeah of course you have to sort tyres and suspension, but why ignore a whole avenue of potential gain?

[Bazda]

im a beleiver of not needing aero unless your doing serious competition racing.

[fxgt race]

Spoliers well worth it, in moderation. Why would you not put something on that is going help your cornering.

[cat007]

Spoliers well worth it, in moderation. Why would you not put something on that is going help your cornering.

Because without proper research and just chucking something on from tardme - you'll end up with an air brake that has little to no downforce

[Mr Revhead]

but that can be said for pretty much anything else on your car
There's a hell of a lot of good data available about aero stuff. I reckon it's actually easier to find than what turbo suits X application. Mainly because so many are so ignorant about it that they don't post as much bs like they do other things

[petrolhead]

Check out http://www.autospeed.co.nz it has heaps of info on car setup and everything he tests to see how effective it is. There is some quite good stuff on aero too.

[molex]

jeez, you lot are all a bit negative aren't you...

I did quite a bit of reading into amateur aerodynamic mods and more importantly, testing to ensure it's actually of benefit.

there's a lot of info out there but you have to think a bit outside of the box. One of the best sources I found of empirically tested aerodynamic mods with proven results was the eco nuts that modify their cars for upteen bizzilion miles to the gallon. Most (but not quite all) of their mods for efficiency translate very well into mods for performance, be it in a straight line or cornering. They have some pretty innovative ideas on how to do it on the cheap too.

I haven't quite got their myself yet, but it's definitely on the cards to make up an undertray/front diffuser/airdam to suit my EP82, I'd be keen to trade ideas/build something together if you're interested.

I even went so far as to take some measurements and do some drawings in sketchup of a two piece undertray with mounts that you could remove in a couple minutes. Damned if I know where the damn file is now though.

[Malcolm]

Spoliers well worth it, in moderation. Why would you not put something on that is going help your cornering.

Because without proper research and just chucking something on from tardme - you'll end up with an air brake that has little to no downforce

I would say the same thing about most modifications - i.e. buying some cheap coilovers off trademe, buying a pod filter or shiney muffler or something similar.

Sometimes the research is easy, sometimes someone else has done the research for you (and sometimes they might even have got it right), but I think that it would be unwise to dismiss an incredibly important aspect of vehicle performance just because there isn't a developed base of "common knowledge" (which may or may not be correct) regarding what works and what doesn't.

I've read some good articles in racecar engineering about aero, and there's certainly some pretty good information around about some of the more basic stuff. Generally the most efficient aerodynamic package would be something that is designed reasonably cohesively so that the features complement, rather than fight each other, but you can still get reasonably good results from a more piecemeal type of approach.

I'd suggest sticking with proven aerofoil designs for wings (this is gonna be tricky in NZ, but you should be able to compare available products to proven ones), try to inform yourself a bit about the priniciple of operation of the parts you're using, and try to understand what the important considerations will be to making the package work. I'd suggest checking your local library to see if they have any books on racecar aerodynamics, or you could buy Simon McBeath's Competition Car Aerodynamics (I think that's what it's called). Some of the concepts might go over your head, depending on your background, but you'll get much better and more authorative ideas from that than you will from a forum like this.

Finally physical testing isn't as hard as it may seem. I've seen some interesting "back yard" experiments including wool-tufts taped all over a car, driven down a highway with someone taking photos from another car, wings being tested by mounting them in the back of a truck/van with bathroom scales for measuring downforce and drag etc. The underbody stuff would be the most tricky to prove emperically, but I'd recommend reading about the design of venturis and the wing-in-ground-effect (or just ground effects, as it's more commonly known). For what it's worth you don't need sideskirts to make an undertray/diffuser work, in fact most cars that make use of an aerodynamic undertray don't have sideskirts (unless they're sliding skirts a la the original Lotus ground effects F1 cars then they're not going to "seal" the airflow much anyway). Usually you'll have the throat (or flat section) of the undertray as close to the ground as possible, so your sideskirts wont be able to sit any lower anyway.

IMO small components like caynards are unlikely to have a big effect; you'd probably be better spending the time improving the big squishy device mounted behind the steering wheel to get the most out of the car.

[frost]

yes but most cars with aero undertrays are not really production cars, mainly single seaters and open wheeler have no use for side skirts,
with production car based racing, almost all use side skirting,

there is no use having a front dam and splitter if the air can fill the low pressure void from coming in from the sides.

the flat under tray is there to speed up the air until it gets to the diffuser, where it is slowed down by a reverse venture, the goal is to make fast flowing low pressure under car, in relation to above the car,
a rear diffuser does not have to be super complex, flat undertray leading to 9 degree venture and "maybe" some plates to direct air around suspension parts,

10degrees is prob too much. if you look at the front of that yellow honda civic, you can see the front lover dam is not horizontal like the side skirts but slighty higher in the front,

the rear diffuser does not always need to direct air to the middle, i suspect its useful for fomula 1 style cars that have to direct the air around the rear suspension arms, in your case you have a beam axle?
it will create a heap more downforce then any foilwing will, and it will even lower the drag of the car by way of Pressure Recovery at the back, for a hatch it will be like vtec kicking in,

this will be a good starting point, i have not tried it myself so dont know how accurate it is.
http://www.instructables.com/id/Measure ... -your-car/

at least then if you start adding stuff and it slows you down too much then you know its not working very well. (air dam at front will slow you down)

i know that my trueno liftback has a cd of .39 according to everywhere i look. thats pretty bloody good for a car that size. the designers did a great job of it.