getting my Si slippery

[dichotomous]

I have an '03 honda civic Si. it looks pretty aero already, but looks can be decieving. I want to make it more aerodynamic so that I have about the same drag at 50 or 60 as I had at 40 before. can anyone give an estimation of the Cd? here be a picture of the car (not mine but its a better picture, mine is about 2" taller from suspension NOT being dropped anymore, mines also white)

here is a nice little drawing with the car as stock (rear wing different)


to start with I am doing a grill block, roughed one out with cardboard but wet slushly snow all the next day, and well, its interesting looking now, and off the car too. here is a picture of the front, not my car again, my plate is in the center above the grill. the whole width will be filled in, and did not get too hot when it was about 30degF out


I also want to make a airdam up front, want to extend it forward as well, to maybe get a little more assurance of the front tires on the ground when I DO go faster.

the first thing I actually did was lower the back of the wing on the car, it looks like it flows nice and smooth, but I dropped the trailing edge about 3-4" and it more follows like a roofline extension.
old wing setup (its adjustable so this was all easy and fast)(this actually IS my car)

new wing setup lowered down to almost roofline extension

I have since applied ductape to help cancel out the vortex generator nature of the wing supports.

the rear bumper is essentiall hollow, and the front under engine is pretty dirty, though the middle of the car is very smooth on the bottom with the exhaust tucked up nicely, so I think some underbody panels up front and in the rear, sealing the rear wheels off from the bumper and smoothing that area out will help greatly, no more parachute, I might even add some ground effects to the rear bumper panel as well, to offset the downforce loss of the wing.

I may do rear wheel skirts, though it looks tough cause the tires come out a little, especially my wide summer tires. if I do this I will be building tire pants as well, including the tire boat tails and spats into the skirts and smoothing it all out. I will likely add some side trim below the car which with the tire spats up front and front tire boattails and rear skirts and front airdam should help to "seal out" the bottom of the car, helping reduce underbody flow and maybe get back even more of that wing's downforce without the aero deficets.

so far thats my plan, I will not be building a kamm back or boat tail, cause I think the rear can be pretty aero once its smoothed out with the bumper and I figure the best rear wing position. also I hate my tailights, so I might pull a mercedes move and duct some underbody or front air to those (dont mind drilling or cutting them at all) to help shape the rear wake a little bit.

I may also do something about the wiperblades, they will stay on since it rains and snows here a LOT, but I may pull a small deflector over them which would cover them completely to the windshield and they would slide up out of it, actually more for snow not clogging them as much for aero (no cold wind a a little heating strip in there and no icy wipers, worth 5mpg to me almost)

I am fortunate because I have an almost unlimited supply of coroplast, since our daycare provider's husband manages a whole bunch of chain convience stores and they just toss those, he said he'd toss them to me if I wanted (I said I was gonna use a bunch for building forts and castles for the kids, which I will though)

right now I am generally getting around 30mpg, with a couple pulse and glide attempts at normal cruising speed getting me up to a high of 42.7mpg. I have also cut off the cold air inlet to my intake, though I dont know that this is helping me yet, just remember its cold here now.

[1.5Ldave]

I would say the wheel skirts and getting the bottom side as smooth as possible would be your biggest gain areas. You also have a relatively new vehicle, so Cd information should be out there somewhere.

Dropping the car reduces the frontal area which helps with drag, so you may want to re-drop it. Also worth noting is unless you have a turbo on that thing you will never reach speeds that need more downforce than came from the factory. (And you would also want the downforce on the front of the vehicle since its front wheel drive)

That wing looks like its going to hurt aero more than help it. I would advise at least testing a partial kammback made of coroplast. Have it follow the same curve as the roofline and cut off at the back of the body.

[dichotomous]

Originally Posted by 1.5Ldave

I would say the wheel skirts and getting the bottom side as smooth as possible would be your biggest gain areas. You also have a relatively new vehicle, so Cd information should be out there somewhere.

Dropping the car reduces the frontal area which helps with drag, so you may want to re-drop it. Also worth noting is unless you have a turbo on that thing you will never reach speeds that need more downforce than came from the factory. (And you would also want the downforce on the front of the vehicle since its front wheel drive)

That wing looks like its going to hurt aero more than help it. I would advise at least testing a partial kammback made of coroplast. Have it follow the same curve as the roofline and cut off at the back of the body.

the rear wing is a nice carbon peice and I'd rather not get rid of it, and, well, I have no idea how its held on. and I think it can be setup for aero, maybe by flipping the wing portion. kammback isnt gonna happen, I dont like those

dropping it will never happen, I live in the land of potholes and snow, I need that height, it was a real problem before, and it corners better, drives better, and is better all around with the new suspension. I will airdam it before it ever goes down again

[dichotomous]

went and got kitchen drawer silicon bumpers to stick on my car, prepped with alcohal and stuck on the sides of my a-pillars, b-pillars, a couple on each c-pillar, a few on the mirrors, and a big string right behind the moonroof, because the flow seperates just a bit behind that and I am hoping they help keep the flow on the roof. also stuck a couple on the insides in front of the wing supports, so help offset the natural vortexs that will generate off those.

the placement is anything but scientific, these areas just looked like they might help keep flow attached to the car to give it a smaller overall aero profile. we shall see.

[MetroMPG]

I'm sure those will work wonders next time you're bouncing off the rev limiter in top gear. Please keep us posted.

[dichotomous]

its winter time! can't do that now! did that once, just to see you know, you gotta know just for the sake of knowing. removed that part anyways, I'm a different guy now, 2 children, 1 wife and a few years wi'll do that, I set my cruise at 50 on the interstate now, not 100. we all grow up eventually

[Hasbro]

The rear wing must be hurting the aero a good bit, it's going in the opposite direction it should be for fe.
I have an 04 Si and have drawn up some ideas and will be trying to apply it to a scale plastic model. Not sure when as I'm also starting a business so it's been a bit tight lately.
I'm getting in the 38-42 mpg area. There are some other EP3 guys on here but not many. Slurp is one.

[NeilBlanchard]

Hi,

Have you tried blocking the upper grill, and/or a partial lower grill block? That and if you can manage to get smooth wheel covers would be the biggest benefit, I think.

[Christ]

Originally Posted by 1.5Ldave

...unless you have a turbo on that thing you will never reach speeds that need more downforce than ...

(And you would also want the downforce on the front of the vehicle since its front wheel drive)

LOL.

Why does everyone think that cars have an axial effect in the center of them? Adding downforce to the rear of the car isn't going to take away from front traction.. it's just going to help rear traction.

I've seen A LARGE NUMBER of ricers who have obviously taken the advice of old-school muscle guys that had no idea what the purpose of downforce is...

I've literally seen 100 cars with their "wings" installed either backwards, or in a fashion that would lift the rear end... not that it will do anything to help front traction...

As far as the turbo comment, HP does not determine top speed, gearing and rev range do. He could have aftermarket parts on that car that you dont know about and have it slightly built (250HP will pretty much top out the tranny in a reasonable amount of time) as an all motor car.

Dichtomous - Is that as far down as the spoiler goes? You could try some clear packaging tape across the negative area (the hole all the way across, between the spoiler and the chassis of the car) and lower it down as far as it will go...

The flow will most likely attach itself to the spoiler and be dragged down so that it reconnects with the lower flow sooner, causing less wake. Keep it 12-15* angle though.

[dichotomous]

christ, I think I can adjust it down a bit lower, some lunch this week I'll do that, or I may flip it when I can get one of the front bolts out, it kinda stripped. flipped it would fill in the negative areas (the end mounts extend to the bottom) and point down a bit better too.

oh, and turbo isnt nessisary, the car has no problem with power and the gears are short. pretty funny that it has the same topend as my bike, though they reach it differently and the car wants more but the bike is all done.


anyways, the bumps seem to be working, if only a little, glide times seem a touch longer, the top bumps are designed to keep the flow from bubbling off the roof, and it does, you can see with rain and snow, if I dont clear the roof off before I drive the snow is all gone from a bit behind the moonroof forward, and from about the antenna back, same with rain, wet there, but not where the wind clears it. drove it after installing, roof was still wet, and after a few miles at 55mph, the roof was dry.

picked up some kids kraft scissors, $5 for a set of 5 of them, all kinds of cool patterns. will try cutting out some tape and installing along with the bumps, might help